Cyanobacteria from the Arabian Peninsula: A Comprehensive Review of Bioactive Compounds, Therapeutic Potential, and Biotechnological Applications

Abstract

Cyanobacterial species in the Arabian Peninsula region display a diverse range of potential biotechnological application. This review summarizes the cyanobacteria diversity found in the Peninsula region, the bioactive compounds found in these species, and the several health benefits and applications. The Arabian Peninsula region comprises a wide range of cyanobacteria with representatives from the orders Oscillatoriales, Chroococcales, Stigonematales, and Nostocales. These microorganisms produce specialized metabolites such as photosynthetic pigments, pigment–protein complexes, lipopeptides, phenolic compounds, and unique secondary metabolites. Many of the metabolites offer beneficial biological functions including antioxidants, antibacterial, anti-cancer, anti-inflammatory antiviral, and neuroprotective ones. In addition to the medical-related practices, cyanobacteria in the Peninsula region might have several other applications. Other probable uses include their potential bioremediation capability to remove pollutants or heavy metals, as a potential biohydrogen source for renewable energy, and as biofertilizers and soil enhancement to support sustainable agriculture; other useful applications include bioplastics production (polyhydroxyalkanoates), soil microbiota improvement, and methane reduction. The review highlights the potential diverse biotechnological applications of Arabian Peninsula cyanobacteria toward bioremediation, bioplastics, ecosystem regeneration, biofertilizers, bioenergy, and agro-sustainability, as well as human health. This review highlights the importance of the further exploration and exploitation of these resourceful microorganisms for sustainable development in the Arabian Peninsula region.

1. Introduction

Cyanobacteria are prokaryotic oxygenic photosynthetic microorganisms that exhibit rapid growth and relatively simple and low-cost growth requirements [1], which positions them as attractive candidates for many biotechnological purposes. These ancient microorganisms evolved over billions of years and represent one of the most flexible and adaptable forms of life on Earth. To date, around 150 genera have been recognized, grouped into four major orders, Chroococcales, Oscillatoriales, Nostocales, and Stigonematales [2]. They are important players in the global ecosystem, particularly in marine habitats where non-heterocystous species were historically underestimated but are now acknowledged as the principle marine N₂ fixers [3].

The Arabian Peninsula offers a unique environment for cyanobacterial proliferation and diversity, with nutrient-rich environments for the large diversity of microalgae. The Peninsula’s favorable temperature, non-arable land, and access to the ocean provide an ideal location for microalgae biomass production [4]. This is paramount given the arid climates of these Peninsula countries rely heavily on imported food products. The key significance of investigating cyanobacteria in this location lies in their ability to contribute to multiple challenges of the current situation, such as environmental remediation, sustainable energy resources, and new medications.

Recent innovations in molecular biology methods such as 16S rRNA sequencing and phylogenetic analysis have revealed an extraordinary diversity of cyanobacterial species across the Peninsula countries (Saudi Arabi, Iraq, Oman, Qatar Bahrain, and United Arab Emirates) [5,6,7]. This includes a range of taxa belonging to different orders (Oscillatoriales Chroococcales, Stigonematales, and Nostocales), each contributing distinctive metabolic capabilities and biotechnological opportunities. Diverse environmental niches, ranging from the groundwater wells in Saudi Arabia [3] to the marine habitats in the southeastern UAE [8] and the wide coastlines in Oman with a diverse water, hosting coral reefs, kelp forests, mangroves, and seagrass beds [9], clearly have offered these organisms a wide variety of metabolic pathways and a wide selection of bioactive compounds. Cyanobacteria have gained the interest of the scientific community for their ability to synthesize various types of specialized metabolites [10], which range from photosynthetic pigments, pigment–protein complexes, and secondary metabolites with substantial biological activities. Their applications have progressed from traditional to inventive uses, including the production of renewable energy by biohydrogen generation, environmental remediation through their capacity to degrade pollutants and heavy metal accumulation, and agriculture sustainability from nitrogen-fixing microorganisms [11].

This review provides a detailed synopsis of our knowledge of the cyanobacteria diversity in the Arabian Peninsula with an assessment of the species distribution across the various countries in the Arabian Peninsula region. It also aims to examine the types of bioactive compounds that are produced by cyanobacterial species and specifically assess their therapeutic potential. Furthermore, this work investigates the broader range of compounds and applications, including their role in biohydrogen production, bioremediation processes, biofertilizer development, and emerging applications in bioplastic production through polyhydroxyalkanoate synthesis. This paper includes their ecological importance; especially regarding reducing methane and soil microbiota improvement, providing an overall evaluation of their potential to help solve modern environmental agricultural issues at large.

While Arabian Peninsula cyanobacteria show promise, a gap remains between laboratory discoveries and field implementation. International examples demonstrate a successful scale-up: Arthrospira cultivation for nutraceuticals in India/China (10,000+ tons/year) [12], Nostoc biofertilizers for semi-arid agriculture in India (15–30% yield increase) [13], Synechococcus for wastewater treatment in Spain (>90% nutrient removal) [14], engineered Synechocystis for PHB production in Germany (25% dry weight) [15], and Chlorella biofuels in the US (20–30 g/m²/day) [16]. These successes suggest that similar pathways are feasible for Arabian Peninsula species, provided the region-specific challenges (extreme temperatures, water scarcity, and dust storms) are addressed through tailored engineering solutions.

2. Species and Bioactive Compounds

2.1. Species Found in Arabian Peninsula

The Arabian Peninsula contains a wide variety of microalgal species, showing different distributions in different countries. In Oman, five hot springs were sampled, and direct microscopy determined there were 12 different unicellular and filamentous morphotypes, including cyanobacteria represented by several genera of the order Synechococcales including Synechococcus and Leptolyngbya, as well as oscillatorial forms like Oscillatoria, Phormidium, and Lyngbya [17]. These findings highlight the adaptability of thermotolerant cyanobacteria to extreme geothermal environments, a pattern that appears recurrent across the arid regions of the Peninsula.

The World Register of Marine Species recognizes the Nostocales represented by Anabaena, Aphanizomenon, Nostoc, and Aphanocapsa, Gloeocapsa, and Chroococcus as members of the Chroococcales. The microalgal diversity of Saudi Arabia was sampled from groundwater wells, water bodies (surface), and freshwater lakes using light microscopy for morphological characterization, and shows a similar pattern, with significant representatives in Chroococcales (Chroococcus minutus, Hydrococcus rivularis, Merismopedia punctata, and Aphanothece clatharta), Nostocales (Cylindrospermopsis raciborskii raciborskii (currently accepted as Raphidiopsis raciborskii), Nostoc sphaericum, and Anabaenopsis arnoldi), and Oscillatoriales (Oscillatoria limnetica and Pseudanabaena catenata) [18,19]. The consistency between Oman and Saudi Arabia suggests that freshwater and geothermal habitats in the Peninsula support a core cyanobacterial community dominated by filamentous and coccoid forms, despite the differences in the sampling environments.

In contrast, the diversity of Kuwait as investigated through 16S rRNA sequencing from Kuwait Bay and four offshore sites in summer and winter shows a majority of Synechococcus and Picocyanobacteria [20]. Qatar’s coastal regions analyzed using 16S rRNA gene sequencing, followed by phylogenetic analysis, harbor unique genera including Geitlerinema, Euhalothece, Geminocystis, and Chroococcidiopsis [5]. This shift toward picocyanobacterial dominance in Kuwait and the presence of specialized genera in Qatar indicate a stronger influence of marine and saline conditions, which favor smaller, more adaptable taxa with high surface-area-to-volume ratios.

The United Arab Emirates (UAE) demonstrates a rich diversity of mat-forming cyanobacteria, particularly in marine environments of the southeastern coast of the Arabian Peninsula at Abu Dhabi, identified through a combination of light microscopy, enrichment cultivation, 16S RNA sequencing, and phylogenic analysis, with species such as Microcoleus chthonoplastes and Lyngbya aestuarii, alongside Phormidium, Entophysalis major, Oscillatoria, and representatives of Chroococcales (Aphanothece, Chroococcus, and Aphanocapsa) [8,21]. Compared to planktonic communities reported in Kuwait and Qatar, the UAE assemblages emphasize benthic, mat-forming cyanobacteria, reflecting the ecological specialization driven by sediment-rich coastal habitats.

Yemen’s microalgal flora, examined through light microscopy from Yemeni fresh-water samples collected from the Aqan and Al-Anad bridges, is characterized by common genera including Spirulina, Oscillatoria, Phormidium, Anabaena, and Cylindrospermum [22]. Iraq presents a particularly diverse assemblage from different water bodies in Mosul, the Tigris River, water bodies in Basrah southern Iraq, and the Diyala River, identified using light microscopy, compound microscopy, conventional PCR, and phylogenetic analysis based on 16S rRNA gene sequences, with several notable species including the first GenBank-registered Gloeocapsa calcarea, and new records to the Iraqi algal flora such as Arthrospira platensis and Limnospira fusiformis [7,23]. The Iraqi diversity spans across multiple orders, including Chroococcales (Gloeocapsa nigrescens, Microcystis robusta, M. flos-aquae, and M. fosaquae), Oscillatoriales (Oscillatoria, Schizothrix, and Plectonema tomasinianum), and Nostocales (Anabaena circinalis, and Nostoc commune), among others [24,25,26] The broader taxonomic diversity observed in Iraq and Yemen, compared to Gulf countries, may be attributed to the presence of more diverse freshwater systems and riverine inputs, which create heterogeneous ecological niches [27] (

Table 1. Distribution and sources of microalgal species in the Arabian Peninsula.

Country	Sample Source/Location	Key Species/Genera Identified	References
Oman	Five hot springs	Synechococcus, Leptolyngbya, Oscillatoria, Phormidium, Lyngbya	[17]
Saudi Arabia	Groundwater wells, surface water bodies, freshwater lakes	Chroococcus minutus, Hydrococcus rivularis, Merismopedia punctata, Aphanothece clatharta, Cylindrospermopsis raciborskii, Nostoc sphaericum, Anabaenopsis arnoldi, Oscillatoria limnetica, Pseudanabaena catenata	[18,19]
Kuwait	Kuwait Bay and four offshore sites (summer and winter)	Synechococcus, Picocyanobacteria	[20]
Qatar	Coastal regions	Geitlerinema, Euhalothece, Geminocystis, Chroococcidiopsis	[5]
UAE (Abu Dhabi)	Marine environments (southeastern coast), mat-forming	Microcoleus chthonoplastes, Lyngbya aestuarii, Phormidium, Entophysalis major, Oscillatoria, Aphanothece, Chroococcus, Aphanocapsa	[8,21]
Yemen	Freshwater (Aqan and Al-Anad bridges)	Spirulina, Oscillatoria, Phormidium, Anabaena, Cylindrospermum	[22]
Iraq	Mosul (various water bodies), Tigris River, Basrah (southern Iraq), Diyala River	Gloeocapsa calcarea (first GenBank-registered), Arthrospira platensis, Limnospira fusiformis, Gloeocapsa nigrescens, Microcystis robusta, M. flos-aquae, M. fosaquae, Oscillatoria, Schizothrix, Plectonema tomasinianum, Anabaena circinalis, Nostoc commune	[7,23,24,25,26]

).

Overall, a comparative synthesis across the Arabian Peninsula reveals a clear ecological pattern: freshwater and geothermal systems tend to support diverse filamentous and heterocystous cyanobacteria, while marine and hypersaline environments favor picocyanobacteria and mat-forming taxa. Despite the regional variability, Chroococcales, Nostocales, and Oscillatoriales consistently dominate, indicating a shared foundational community structure shaped by the arid climate and high-salinity conditions characteristic of the region. This convergence suggests that environmental drivers, rather than geographic boundaries, play a dominant role in structuring the microalgal diversity across the Peninsula.

2.2. Bioactive Compounds and Secondary Metabolites

The most active cyanobacterial species producing secondary metabolites were reported in 2018 to belong to the order Oscillatoriales (49%), followed by Nostocales (26%), Chroococcales (16%), Pleurocapsales (6%), and Stigonematales (4%) [28]. This distribution suggests a taxonomic bias in biosynthetic potential, where filamentous cyanobacteria, particularly Oscillatoriales and Nostocales, contribute disproportionately to the metabolite diversity compared to unicellular groups.

Cyanobacterial secondary metabolites contain various bioactive molecules including cytotoxic (41%), antitumor (13%), antiviral (4%), and antimicrobial (12%) ones, and other compounds (18%) include antimalarials, antimycotics, multidrug-resistance reversers, herbicides, insecticides, algaecides, and immunosuppressive agents [29]. Collectively, this broad spectrum of bioactivities highlights the pharmacological and biotechnological relevance of cyanobacteria, although the relative abundance of cytotoxic compounds indicates a strong ecological role in defense and competition. The isolated bioactive compounds include polyketides, amides, alkaloids, fatty acids, indoles, and lipopeptides [11]. Despite this diversity, a clear pattern emerges in which pigment-related compounds are consistently reported across multiple genera, whereas specialized metabolites tend to be species-specific, reflecting the differences in ecological function and metabolic specialization.

The literature review showed that, in the Arabian Peninsula, over 30 cyanobacterial strains were detected and shown to produce various bioactive compounds (Table 1). The reported compounds can be categorized into several major groups: pigment–protein complexes (phycobiliproteins including C-phycocyanin, phycoerythrin, and allophycocyanin), photosynthetic pigments (chlorophylls and carotenoids), phenolic compounds, and various specialized metabolites as shown in Table 1.

Several species demonstrate notable compound diversity. Several species have considerable variability in compounds. For example, Chroococcus has multiple compounds including lipopeptides, biosurfactants, vitamins, chlorophyll, and phyco-biliprotein [30]. Spirulina generates complex mixtures of unsaturated fatty acids, amino acids, carotenoids and phenolic compounds [31]. In comparison, these genera exhibit broad-spectrum metabolic profiles dominated by primary and nutraceutical compounds, contrasting with other taxa that produce more structurally specialized and bioactive metabolites.

Some species have unique compounds, with Aphanothece clatharta producing sacran, a sulfated polysaccharide [32] and Lyngbya aestuarii producing specialized metabolites of dragonamide C and 2,5-dimethyldodecanoic acid [33]. Compounds can also range the diversity of specialized metabolites with unique or specific structures. Nostoc species produce cyanovirin-N and nostocyclopeptides [34,35] and Cylindrospermopsis raciborskii produces cylindrospermopsin and saxitoxin, a severe neurotoxin [36]. Aphanizomenon is unique with the production of C phycocyanin, β-phenylethylamine, and omega-3 PUFAs [37]. Oscillatoria species produces acetylated sulfoglyco-lipids and variable methanolic compounds [38,39], while Leptolyngbya halophile produces some flavonoids like luteolin-7-glucoside and naringenin [40]. This comparison highlights a functional divergence, where some genera are associated with bioactive and potentially toxic metabolites, while others contribute mainly to antioxidant and nutraceutical compound pools.

Several genera are specifically abundant in pigment-related compounds. Arthrospira platensis and Limnospira fusiformis both produce a range of photosynthetic pigments including, but not limited to, phycocyanin, allophycocyanin, phycobiliproteins, and various forms of chlorophyll [41,42]. The Chroococcidiopsis genera are differentiated by their production of chlorophyll-a, total carotenoids, phycocyanin, and allophycocyanin [43], where Geminocystis produces multiple types of phycobiliproteins and methyl palmitate [44,45]. Entophysalis major produces scytonemin [46], while Cylindrospermum produces a unique cyclic lipopeptide, puwainaphycins [47]. This distinction suggests that, while pigment production is a conserved trait linked to photosynthetic efficiency, the synthesis of secondary metabolites such as lipopeptides and UV-protective compounds (e.g., scytonemin) reflect adaptive responses to environmental stressors such as high irradiance and salinity. Chroococcidiopsis cubana produces capric acid, as a secondary metabolite [48], and, finally, Westiellopsis prolifca can produce quercetin [49].

The metabolite profile comprises compounds that can be extracted and some strains generate bioactive metabolites with different extraction methods. Microcoleus chthonoplastes produces bioactive compounds through aqueous and methanol extracts [50], and Euhalothece produces bioactive glycolipids and phospholipids with methanol extraction [51]. Oscillatoria limnetica is also highlighted to serve a valuable asset in green synthesis when its aqueous extract is utilized to generate silver nanoparticles [52]. A classification of cyanobacterial metabolites based on their chemical structure and functional roles is presented in Figure 1. These variations indicate that methodological differences in extraction significantly affect the detected metabolite profile, which may partly explain inconsistencies between studies and highlights the need for standardized extraction protocols to enable reliable comparison.

Overall, a comparative synthesis reveals that cyanobacteria in the Arabian Peninsula exhibit both conserved and specialized metabolic traits. While pigment-related compounds are ubiquitous across taxa, reflecting their essential role in photosynthesis, the distribution of secondary metabolites is highly species- and environment-dependent. Filamentous cyanobacteria, particularly those from Oscillatoriales and Nostocales, emerge as key contributors to the bioactive compound diversity, especially in terms of pharmacologically relevant and toxic metabolites. This duality underscores both the biotechnological potential and ecological significance of cyanobacterial metabolites, while also highlighting the need for more standardized and integrative studies to fully exploit their applications.

2.3. Therapeutic Potential

Cyanobacterial species from the Arabian Peninsula have diverse biological activity with their specialized metabolites and compounds. The therapeutic application can be organized into some major categories within a functional group (

Table 2. Bioactive compounds and biological activities of cyanobacteria species of the Arabian Peninsula.

Species of Cyanobacteria	Bioactive Compounds	Biological Activity	References
Synechococcus	Bioactive lipopeptides	Anti-inflammatory	[53]
Anabeana	Anatoxin-a	Neurotoxin (inflammatory), antioxidant	[54]
Gloeocapsa	Uronic acids (galacturonic and glucuronic)	Antioxidant, metal-chelating	[55]
Chroococcus	Bioactive lipopeptides, biosurfactant, vitamin, chlorophyll, and phycobiliprotein	Anti-microbial	[30]
Aphanizomenon	C-phycocyanin, β-phenylethylamine, omega-3 PUFAs	Anti-inflammatory	[37]
Leptolyngbya	Chlorophylls, carotenoids, phenolics, and flavonoids	Antioxidant, anti-carcinogenic	[56]
Oscillatoria	Acetylated sulfoglyco-lipids Methanolic compounds	Anti-viral, anti-bacterial	[38,39]
Phormidium	C-phycocyanin	Hepatoprotective	[53]
Spirulina	Unsaturated fatty acids, amino acids, carotenoids, and phenolic compounds	Antioxidant, anti-carcinogenic, neuroprotective	[31]
Nostoc	Cyanovirin-N Nostocyclopeptides	Anti-viral, anti-toxic, antioxidant, anti-carcinogenic	[35,34]
Cylindrospermopsisraciborskii	Cylindrospermopsin Saxitoxin	Hepatotoxic and genotoxic effects Neurotoxin	[36]
Aphanothece clatharta	Sacran (sulfated polysaccharide)	Anti-inflammatory	[32]
Oscillatoria limnetica	Aqueous extract of Oscillatoria limnetica fresh biomass was used for the green synthesis of Ag-NPs	Anti-bacterial, nanoparticles as anticancer drug	[52]
Pseudanabaena catenata	Phycoerythrins, methanolic compounds	Pigment, anti-bacterial, anti-fungal	[57,58]
Anabaenopsis arnoldi	Microcystin	Cyanoginosin	[19]
Synechococcus (Picocyanobacteria)	β-N-methylamino-l-alanine microcystin	Neurotoxin (inflammatory), cyanoginosin	[59]
Geitlerinema	Phycocyanin	Anti-cancer drug (cytotoxic response to human lung tumor cells)	[5]
Euhalothece	Methanolic extract (glycolipids and phospholipids)	Anti-bacterial, anti-fungal, anti-oxidant	[51]
Geminocystis	Phycobiliproteins (C-phycocyanin, phycoerythrin, allophycocyanin), methyl palmitate	Antioxidant, anti-lipid peroxidation capacity	[44,45]
Chroococcidiopsis	Chlorophyll-a, total carotenoids, phycocyanin, and allophycocyanin	Enhance immune response, reduce nuclear damage	[43]
Microcoleus	Methanol and hexane extracts	Anti-bacterial, anti-fungal	[60]
Lyngbya aestuarii	Dragonamide C, 2,5-dimethyldodecanoic acid,	Anti-bacterial, anti-fungal, herbicidal activity	[33]
Entophysalis major Ercegovi	Scytonemin	Anti-inflammatory, enzyme inhibition	[46]
Microcoleus chthonoplastes	Aqueous and methanolic extracts	Anti-bacterial	[50]
Aphanothece (Halothece)	Phenolic compounds Phycobiliproteins	Antioxidant	[59,61]
Cylindrospermum	Cyclic lipopeptides puwainaphycins	Anti-fungal	[47]
Schizothrix	Schizotrin A	Anti-bacterial, anti-fungal	[62]
Westiellopsis prolifca	Quercetin	Improvement in cognitive function, neuroprotective and anti-neuroinflammatory	[49]
Cyanobacterium aponinum	C-phycocyanin	Antioxidant, anti-bacterial, anti-cancer, anti-inflammatory	[63]
Leptolyngbya halophile	Luteolin-7-glucoside and naringenin	Antioxidant, nephroprotective, neuroprotective, anti-cancer, anti-atherosclerotic	[40]
Chroococcidiopsis cubana	Capric acid	Anti-bacterial, anti-fungal, anti-viral, anti-inflammatory	[48]
Arthrospira indica/ Arthrospira platensis	Phycocyanin, allophycocyanin, phycobiliproteins, chlorophyll a, chlorophyll b	Antioxidant, anti-diabetic, anti-microbial, anti-neoplastic, anti-inflammatory	[42]
Limnospira fusiformis	Phycocyanin, polysaccharides, and carotenoids	Antioxidant, anti-inflammatory, immunomodulatory, Anti-viral, anti-cancer, anti-diabetic, lipid-lowering	[41]

); many species demonstrate several bioactivities through various mechanisms. This multifunctionality indicates that cyanobacterial metabolites are not limited to single therapeutic targets, but, rather, act through overlapping biochemical pathways, enhancing their potential as broad-spectrum therapeutic agents.

Although there is great therapeutic potential in using microalgal bioactives, they first need to undergo a thorough examination of their safe use in humans [64]. In addition to producing the potentially dangerous hepatotoxins (microcystins) and accumulating heavy metals, the prolonged intake of microalgae has also been associated with liver damage [65,66]. Some hypersensitive reactions, including anaphylaxis, have also been reported from the ingestion of Arthrospira and Chlorella [67]; and the possible immunomodulation effects could be hazardous for autoimmune disease patients [68]. Additionally, drug interaction is another factor that needs to be considered; e.g., it has been shown that Chlorella potentiates warfarin’s anticoagulant activity [69]. Finally, a lack of standardization among regulatory agencies regarding the use of microalgal medicines presents some difficulties in terms of the stability of strains used for production and the accurate identification of species [64,70]. Therefore, a comprehensive toxicologic profile, the determination of allergenicity, and the determination of pharmacokinetics will be required prior to receiving FDA approval and the regulatory framework will need to develop to adequately manage the risk inherent in the biologically unique properties of these products [64,66,70].

2.3.1. Anti-Microbial Activity

The anti-microbial compounds derived from cyanobacteria are emerging as a potential source of new therapeutic candidates as highlighted by the concerns for increasing antimicrobial resistance [71]. These compounds exhibit activity against bacteria, fungi, and viruses through diverse mechanisms of action. Collectively, cyanobacterial metabolites demonstrate both broad-spectrum and targeted antimicrobial effects, suggesting their potential as alternatives or complements to conventional antibiotics.

The genus Nostoc was shown to express a suite of activities based on cyanovirin-N, which shows a particularly potent anti-viral effect; furthermore, its nostocyclopeptides secondary metabolite exhibit both an anti-toxin and antimicrobial actions [34,35]. Lyngbya aestuarii also produces specialized metabolites like dragonamide C and 2,5-dimethyldodecanoic acid which showed site-specific anti-bacterial and anti-fungal activity, indicating the exploration of novel anti-microbial agent development [33]. Chroococcidiopsis cubana produces capric acid which exhibited a full-spectrum activity anti-microorganism profile including anti-bacterial, anti-viral, anti-fungal, and anti-inflammatory properties [48]. This comparison highlights a key distinction between species producing highly specific antimicrobial compounds and those with broad-spectrum activity, reflecting the differences in ecological roles and potential clinical applications.

2.3.2. Anti-Inflammatory Activity

The anti-inflammatory compounds derived from cyanobacteria offer a choice to treat several inflammatory conditions through multiple molecular pathways in a variety of disorders. They can modulate inflammatory responses and provide protection from inflammation-arbitrated disorders [53,71]. These compounds not only suppress inflammation but may also modulate immune responses, making them relevant for chronic and multifactorial inflammatory diseases.

The species belonging to genus Synechococcus produce anti-inflammatory lipopeptides that efficiently inhibit inflammation [53]. Aphanothece sp. produces a specialized sulfated polysaccharide, sacran, that has specific anti-inflammatory effects [32,72]. Entophysalis major produces the scytonemin pigment that has anti-inflammatory effects and can inhibit enzymes [46]. The anti-inflammatory effects found in these compounds work over a range of different molecular pathways, which opens interesting therapeutic diagnoses for biologics to have complementary effects. In contrast to single-compound systems, these species exhibit structurally diverse anti-inflammatory agents, suggesting that cyanobacteria provide multiple mechanistic pathways for inflammation control, including enzyme inhibition, signaling modulation, and oxidative stress reduction.

2.3.3. Antioxidant Activity

Cyanobacterial antioxidant compounds have been recognized for their significant protective effects against oxidative stress and other related cellular injuries and suggest therapeutic opportunities in reducing oxidative stress and various disease states. Antioxidant effects cover other key undergone mechanic antioxidants, including free radical scavengers, and metal chelation [51]. Across studies, antioxidant activity emerges as one of the most consistently reported functional properties, indicating its fundamental role in cyanobacterial survival under extreme environmental conditions.

Antioxidant effects belong to another key category, and they are produced by several cyanobacteria, with protective activity against oxidative stress through different mechanisms. Gloeocapsa produced uronic acids, namely, galacturonic and glucuronic acids, which display both antioxidant protection and metal-chelating activity [50]. Leptolyngbya produces a complex mixture of chlorophylls, carotenoids, phenolics, and flavonoids, which cause the antioxidant and anticarcinogenic effects [56]. Arthrospira platensis and Limnospira fusiformis produced a variety of compounds that include phycocyanin, allophycocyanin, phycobiliproteins, and several chlorophylls which contribute to their strong antioxidant potential [41,42]. Comparatively, pigment-rich species tend to exhibit a stronger antioxidant capacity, suggesting a direct relationship between photosynthetic pigment composition and oxidative stress mitigation.

2.3.4. Neuroprotective Activity

Neuroprotective compounds from cyanobacteria hold potential in the treatment of neurodegenerative diseases and cognitive enhancement through numerous mechanisms including anti-neuroinflammatory properties, and neural protection [73]. Although less extensively studied than antioxidant or antimicrobial activities, neuroprotective effects represent an emerging area with significant therapeutic promise.

Neuroprotective and cognitive enhancement properties have been demonstrated by a number of species. For example, Westiellopsis prolifca contains quercetin compounds that increase cognitive function along with neuroprotective and anti-neuroinflammatory properties [49]. Leptolyngbya halophile contains specific flavonoids, luteolin-7-glucoside and naringenin, with neuroprotective, nephroprotective, and anti-atherosclerotic effects [40]. Moreover, several species have anticancer effects through various mechanisms. Geitlerinema produces phycocyanin that displayed a specific cytotoxic effect towards human lung tumor cells [5]. Spirulina produces a mixture of unsaturated fatty acids, amino acids, carotenoids, and phenolic compounds that hold anticarcinogenic properties, antioxidants, and neuroprotective effects [31]. This overlap between neuroprotective, antioxidant, and anticancer activities suggests that many cyanobacterial metabolites act through interconnected pathways, particularly those involving oxidative stress and inflammation.

2.3.5. Immunomodulatory and Metabolic Effects

Compounds produced by cyanobacteria with immunomodulatory and metabolic properties can be considered for therapeutic use in regulating the immune system, or for metabolic diseases [74]. These effects are often closely linked to anti-inflammatory and antioxidant mechanisms, indicating a convergence of therapeutic functions within the same compounds.

These compounds can act on the immune response or metabolic activity through different mechanisms. Phormidium makes C-phycocyanin, which is hepatoprotective [53]. Geminocystis produces many phycobiliproteins, and methyl palmitate that have an antioxidant and anti-lipid peroxidation capacity [44,45]). The Aphanizomenon produces C-phycocyanin, β-phenylethylamine, and omega-3 PUFAs, and, together, these contribute to its anti-inflammatory effects [37]. The relationships between cyanobacterial metabolites, their biological activities, and downstream applications are summarized in Figure 2, highlighting the integrated structure–function–application framework. In comparison to single-function compounds, these metabolites demonstrate integrated therapeutic roles, supporting their potential use in complex disorders such as metabolic syndrome and immune dysregulation.

3. Applications

3.1. Cyanobacteria as Biohydrogen Source

Cyanobacteria represent a promising source of biohydrogen, offering significant advantages in renewable energy production. As the purest and most valuable biofuel, hydrogen shows great potential as an environmentally friendly energy carrier for the future [75]. Compared to conventional hydrogen production methods (e.g., fossil fuel reforming), cyanobacterial systems offer a sustainable, carbon-neutral alternative, although their efficiency remains a key limitation. These photosynthetic microorganisms possess a complex enzymatic system for hydrogen metabolism, comprising two groups of enzymes: nitrogenases and hydrogenases. While nitrogenases catalyze hydrogen production alongside nitrogen reduction to ammonia, hydrogenases facilitate the reversible hydrogen reduction from protons and electrons, playing a crucial role in releasing the excess reducing agents during transitions from anaerobic darkness to light conditions [76]. The coexistence of these two enzymatic pathways provides metabolic flexibility; however, their relative contributions vary across species and environmental conditions, influencing the overall hydrogen yield.

Under normal cultivation conditions, photosynthetic microorganisms channel their photosynthetic energy into their own metabolism rather than H2 production, with energy conversion occurring in two membrane-bound reaction complexes: photosystems I and II. However, hydrogen production can be triggered under specific conditions such as oxygen, nitrogen, or sulfur starvation, although all three types of enzymes show a high sensitivity to O₂ content [1]. This creates a fundamental trade-off between photosynthetic oxygen evolution and hydrogen production efficiency, representing a major bottleneck in large-scale applications.

Numerous cyanobacterial genera demonstrate hydrogen production capabilities, including Anabaena, Calothrix, Oscillatoria, Cyanothece, Nostoc, Synechococcus, Microcystis, Gloeobacter, Aphanocapsa, Chroococcidiopsis, and Microcoleus [11], with many of these species being native to the Arabian Peninsula, as demonstrated in Table 3. Despite this broad taxonomic distribution, hydrogen production efficiency varies significantly between genera, reflecting the differences in the metabolic pathways, enzyme activity, and environmental adaptability. Hydrogen metabolism is particularly well-studied in Synechocystis, Synechococcus, Cyanothece, Oscillatoria, Anabaena, and Nostoc, with hydrogen evolution rates varying from 0.001 to 465 mmol H2 (mg Chl a h)⁻¹ [1]. This wide variability indicates a lack of standardization in experimental conditions and highlights the importance of strain selection and optimization in maximizing biohydrogen production.

Notably, Synechococcus PCC 7942 has achieved remarkable results with hydrogen yields of 162.52 μmol/mg chl/h, while Synechocystis PCC 6803 has demonstrated yields of 18.4 μL H2/mg chl/h [75]. In comparison, these strains represent contrasting performance levels, suggesting that genetic and physiological differences strongly influence hydrogen productivity. These organisms are particularly effective due to their unique and labile pigment composition, which enables light absorption across a wide wavelength range, with potential hydrogen release rates comparable to photosynthesis rates [75]. This relationship underscores the critical role of light-harvesting efficiency in driving biohydrogen generation.

Photobioreactors (PBRs) of various types have been utilized extensively for large-scale biomass production and bioenergy in a range of applications [76]. In the case of the Arabian Peninsula, both flat panel and raceway pond production systems were determined to be the most economical, resulting in biomass production costs as low as 2.9 €⋅kg⁻¹, which could be further lowered by up to 42.5% by adopting improved photosynthesis efficiencies and 25% by maintaining higher culture temperatures [4]. Comparatively, open systems such as raceway ponds offer lower operational costs but may suffer from contamination and environmental variability, whereas closed PBR systems provide better control but at higher capital costs. This trade-off highlights the need to balance economic feasibility with process efficiency in large-scale applications.

Overall, a comparative synthesis indicates that, while cyanobacteria hold strong potential for sustainable biohydrogen production, their practical implementation is constrained by low yields, oxygen sensitivity, and variability across species and cultivation systems. Advances in strain engineering, metabolic optimization, and reactor design are essential to overcome these limitations and enable scalable biohydrogen production, particularly in high-irradiance regions such as the Arabian Peninsula.

Table 3. Cyanobacteria species of the Arabian Peninsula that produce hydrogen with their optimal growth conditions for maximum production yield.

Species of Cyanobacteria	Pretreatment Condition	Maximum Hydrogen Yield	Reference
Oscillatoria acuminata	Biological pretreatment + Mg-Zn Fe2O4 NPs using coculture dark fermentation	166.98 μmol H2 mg−1 Chl a h−1	[77]
Anabaena variabilis	Dark fermentation	8.67 μmol H2 mg−1 Chl a h−1	[76]
Synechococcus elongatus	Dark fermentation of suspensions of nitrogen-depleted PAMCOD cells	6.554 μmol H2 mg Chl a−1 h−1	[78]
Synechococcus elongatus	Dark anaerobic fermentation	0.00076 μmol H2 mg−1 Chl a h−1	[79]
Synechococcus elongatus	Dark anaerobic fermentation	0.002 μmol H2 mg−1 Chl a h−1
Phormidium keutzingianum	Co-culture with activated sludge bacteria and sorbitol as carbon substrates	980 mL H2/L	[80]
Anabaena	Amylase followed by thermophilic fermentation for 24 h	1600 mL L−1	[81]
Nostoc linckia	25 days by maintaining required anoxic conditions and carbohydrate supplement	132 μmol H2 mg−1 Chl a h−1	[82]

Table 3. Cyanobacteria species of the Arabian Peninsula that produce hydrogen with their optimal growth conditions for maximum production yield.

Species of Cyanobacteria	Pretreatment Condition	Maximum Hydrogen Yield	Reference
Oscillatoria acuminata	Biological pretreatment + Mg-Zn Fe2O4 NPs using coculture dark fermentation	166.98 μmol H2 mg−1 Chl a h−1	[77]
Anabaena variabilis	Dark fermentation	8.67 μmol H2 mg−1 Chl a h−1	[76]
Synechococcus elongatus	Dark fermentation of suspensions of nitrogen-depleted PAMCOD cells	6.554 μmol H2 mg Chl a−1 h−1	[78]
Synechococcus elongatus	Dark anaerobic fermentation	0.00076 μmol H2 mg−1 Chl a h−1	[79]
Synechococcus elongatus	Dark anaerobic fermentation	0.002 μmol H2 mg−1 Chl a h−1
Phormidium keutzingianum	Co-culture with activated sludge bacteria and sorbitol as carbon substrates	980 mL H2/L	[80]
Anabaena	Amylase followed by thermophilic fermentation for 24 h	1600 mL L−1	[81]
Nostoc linckia	25 days by maintaining required anoxic conditions and carbohydrate supplement	132 μmol H2 mg−1 Chl a h−1	[82]

3.2. Cyanobacteria for Bioremediation

Cyanobacteria offer numerous advantages that make them more efficient than microorganisms like fungi, yeast, and mosses in bioremediation applications. First, they have a more substantial mucilage, which, in turn, increases the binding capacity. Additionally, their high surface area and simplistic nutritional requirements represent a unique advantage in remediation applications [54]. Collectively, these structural and physiological traits provide cyanobacteria with superior adsorption and assimilation capabilities, particularly in nutrient-limited or extreme environments where other microorganisms may be less competitive. Research supported the metabolic flexibility of cyanobacteria when investigating the photoheterotrophic and chemohetertrophic growth of 38 strains [77]. This metabolic versatility enables cyanobacteria to adapt to diverse environmental conditions, thereby expanding their applicability across different types of pollutants and ecosystems.

Specifically, cyanobacteria show promise in degrading a variety of organic pollutants; they are particularly effective in degrading hydrocarbons. For example, cyanobacteria can oxidate polycyclic aromatic hydrocarbons (PAHs) in crude oil [83]. Gupta [84] showed that a consortium of cyanobacterial species, including Oscillatoria salina, Plectonema terebrans, and Aphanocapsa sp., removed components of crude oil such as aliphatics, waxes, bitumen, and aromatic compounds. In addition, Ugboma [85] showed that halotolerant Oscillatoria sp. has also measured a decreased hydrocarbon concentration from 8.992 mg/L to 1.486 mg/L when supplied with NPK fertilizer. In comparison to single-species systems, these findings suggest that cyanobacterial consortia may enhance the degradation efficiency through synergistic interactions, while nutrient supplementation further accelerates pollutant removal.

In recent decades, cyanobacteria have shown promise in treating wastewater types including aquaculture, swine, and sewage [86]. This efficiency is greatly related to their ability to harvest carbon dioxide from the atmosphere and utilize nutrients from wastewater simultaneously, which is effective in treatment as well as in producing valuable carbohydrate- and protein-rich biomass [87]. This dual functionality distinguishes cyanobacteria from conventional treatment systems, as they integrate waste remediation with resource recovery, thereby enhancing process sustainability.

Cyanobacteria have known capabilities to remediate heavy metals that have been listed by the World Health Organization (WHO) as serious environmental issues. For example, Anabaena oryzae and Cyanosarcina fontana actively take up high amounts of iron, lead, copper, and manganese from sewage wastewater, as shown in Table 4 [88]. These species demonstrate active uptake mechanisms, in contrast to the passive adsorption observed in some other microorganisms, which may contribute to higher removal efficiencies. The ability of cyanobacteria to use inorganic acid and phosphorus permits them to positively grow in wastewater settings [89].

In addition, for lead remediation, the Gloeocapsa species were effective, reaching a maximum lead accumulation of 232.56 mg g⁻¹, with decreased efficiency occurring at higher lead concentrations [90]. Oscillatoria sp. was also found to remediate multiple heavy metals—lead, cadmium, copper, zinc, cobalt, chromium, iron, and manganese—through the creation of extracellular bioflocculants while under metal stresses [91]. The geographical distribution and habitat-driven diversity of cyanobacterial communities across the Arabian Peninsula are summarized in Figure 3. This comparison indicates that, while some species specialize in the high-capacity accumulation of specific metals, others exhibit broader multi-metal remediation capabilities, reflecting different physiological adaptation strategies.

The combination of a high metal sorption capacity and rapid multiplication rates makes cyanobacteria particularly promising for treating contaminated effluents [84]. Overall, a comparative synthesis reveals that cyanobacteria outperform many conventional microorganisms in bioremediation due to their combined abilities for adsorption, biodegradation, and biomass generation. However, the variability in species performance, environmental conditions, and pollutant types highlights the need for targeted strain selection and process optimization to maximize remediation efficiency.

Cyanobacteria from the Arabian Peninsula identified in Table 4 were primarily found in their respective native habitats. For example, Synechococcus and Leptolyngbya are both native to the Omani Hot Springs [17]; while Microcoleus chthonoplastes and Lyngbya aestuarii are native to the coastal mats of Abu Dhabi [8,21], Picocyanobacteria are native to Kuwait Bay [20]; Geitlerinema and Chroococcidiopsis are native to coasts of Qatar [5]; and Arthrospira platensis and Limnospira fusiformis are native to the freshwater bodies of Iraq [7,23]. While there exists considerable variation among cyanobacterial strains in terms of their biomass production capabilities, it has been demonstrated that Arthrospira platensis can produce up to 0.18 g/L/day, Synechococcus spp. will produce approximately 0.09 g/L/day, and, based upon culture conditions, Chlorella-like species (UAE) have been shown to vary from 0.11 to 0.05 g/L/day [17,21,23]. Nonetheless, the majority of these cyanobacterial species lack documented or reported biomass productivity data which represents an additional area of needed research as high biomass productivity is a critical factor in determining whether or not a specific strain is economically viable for use in wastewater treatment applications, in addition to the ability to remove nutrients from wastewater.

Table 4. Bioremediation by cyanobacteria species found in the Arabian Peninsula according to type of pollution and removal efficiency.

Species	Type of Pollution	Removal Efficiency (%)	References
Oscillatoria	Crude oil contamination in water systems	83.5	[85]
Synechococcus elongatus	Nutrient (NH4+, NO3−, and PO43−) for bioremediation of mixed wastewater (combination of sturgeon and swine wastewater)	67.15 for orthophosphate, 93.39 for nitrate–nitrite, and 97.98 for ammonia	[87]
Synechococcus elongatus	Malachite green in fish tissues and freshwater	99.5	[92]
Anabaena aequalis	Industrial effluents (heavy metal)	BOD and COD recorded 91.18 and 82.54%	[93]
Phormidium mucicola	Industrial Effluents (suspended solids)	53.23	[93]
Microcystis aeruginosa	Heavy metals	92	[94]
Synechocystis sp.	Heavy metals	86	[95]
Synechocystis sp.	Heavy metals	90	[96]
N. muscorum	Heavy metals	80.04	[97]
S. platensis	Heavy metals	87.69	[98]
S. platensis	Heavy metals	100	[99]
S. platensis	Heavy metals	37	[100]
Synechocystis sp. PCC 7806	Heavy metals	75.4	[101]
N. muscorum, Synechocystis sp.	Heavy metals	96.3, 77%	[97,102]
M. aeruginosa	Heavy metals	86	[94]

Table 4. Bioremediation by cyanobacteria species found in the Arabian Peninsula according to type of pollution and removal efficiency.

Species	Type of Pollution	Removal Efficiency (%)	References
Oscillatoria	Crude oil contamination in water systems	83.5	[85]
Synechococcus elongatus	Nutrient (NH4+, NO3−, and PO43−) for bioremediation of mixed wastewater (combination of sturgeon and swine wastewater)	67.15 for orthophosphate, 93.39 for nitrate–nitrite, and 97.98 for ammonia	[87]
Synechococcus elongatus	Malachite green in fish tissues and freshwater	99.5	[92]
Anabaena aequalis	Industrial effluents (heavy metal)	BOD and COD recorded 91.18 and 82.54%	[93]
Phormidium mucicola	Industrial Effluents (suspended solids)	53.23	[93]
Microcystis aeruginosa	Heavy metals	92	[94]
Synechocystis sp.	Heavy metals	86	[95]
Synechocystis sp.	Heavy metals	90	[96]
N. muscorum	Heavy metals	80.04	[97]
S. platensis	Heavy metals	87.69	[98]
S. platensis	Heavy metals	100	[99]
S. platensis	Heavy metals	37	[100]
Synechocystis sp. PCC 7806	Heavy metals	75.4	[101]
N. muscorum, Synechocystis sp.	Heavy metals	96.3, 77%	[97,102]
M. aeruginosa	Heavy metals	86	[94]

3.3. Cyanobacteria as Biofertilizers

Cyanobacteria have also emerged as efficient and sustainable alternatives to chemical fertilizers, offering significant benefits for plant growth, crop production, and soil quality enhancement. These microorganisms serve as valuable biofertilizers due to their diverse metabolic capabilities [103]. Compared to conventional chemical fertilizers, cyanobacteria provide a multifunctional approach by simultaneously improving nutrient availability, soil structure, and plant physiological responses [104,105]. Their effectiveness has been well-documented across various crops, including rice, barley, cotton, tomatoes, oats, radish, sugarcane, chili, maize, and lettuce [2], indicating broad applicability across different agricultural systems and climatic conditions.

Cyanobacteria have been reported to enhance soil fertility through several mechanisms such as maintaining soil structure through polysaccharide-mediated soil aggregation, fixing atmospheric nitrogen, improving soil porosity through adhesive substance production, and secreting growth-promoting hormones such as auxins, gibberellins, vitamins, and amino acids [106,107]. This combination of physical, chemical, and biological effects distinguishes cyanobacteria from single-function fertilizers, positioning them as integrated soil conditioners rather than mere nutrient suppliers.

Nostoc and Anabaena species are well-known examples that can fix 20–25 kg and 60 kg of nitrogen per hectare per season, respectively [2]. In comparison, Anabaena demonstrates a higher nitrogen fixation capacity, suggesting species-specific variability that can be strategically exploited depending on crop requirements and soil conditions. Research has demonstrated (Table 4) their potential as partial substitutes for chemical fertilizers, with studies showing that biofertilization using a mixture of nitrogen-fixing cyanobacteria (Nostoc commune, N. linckia, Nostoc sp., and Anabaena iyengarii var. tenuis) allowed for a 50% reduction in nitrogen fertilizer use while maintaining an equivalent rice grain yield and quality [108]. This finding highlights a key advantage of cyanobacterial biofertilizers in reducing chemical input dependency without compromising productivity.

The experimental evidence supports their growth-promoting effects, as demonstrated by [109], who observed significant improvements in maize seed germination, seedling growth indices, and chlorophyll content when treated with Phormidium sp. ISC108. The combination of Nostoc minutum and Anabaena spiroides with organic fertilizer has shown particularly impressive results, increasing the broad bean dry weight by 41% and 103% compared to full chemical and organic fertilizer applications, respectively [110]. In comparison to standalone fertilizer systems, these synergistic combinations demonstrate enhanced performance, suggesting that integrating cyanobacteria with organic amendments can amplify plant growth outcomes.

Overall, a comparative synthesis indicates that cyanobacteria function as multifunctional biofertilizers by integrating nutrient supply, soil conditioning, and plant growth stimulation. While their effectiveness varies depending on the species, crop type, and environmental conditions, their ability to partially replace chemical fertilizers and improve soil health underscores their potential for sustainable agriculture (

Table 5. Cyanobacteria of the Arabian Peninsula as biofertilizers for different types of plants with the percentage yield increase.

Genus/Species	Type of Plant	Results	References
Oscillatoria	Okra	19.3% of yield increment	[111]
	Rice plants	Combination with other fertilizers (not nitrogen) resulted in healthier growth, and increase in straw and grain yield	[112]
Nostoc	Rice crops	Nostoc piscinale increased chlorophyll a, matched commercial fertilizer in promoting rice growth, and lowered soil pH before planting, making it a promising nitrogen source.	[113]
	Corn	Addition of Nostoc increased plant height and leaf number of plants	[114]
Anabena	Rice plants	Using 10 tons ha−1 of fresh Anabaena azollae on rice plants is as efficient as basal application of 30 kg of N	[115]
	Flooded rice fields	Three of five Anabeana Azolla strains survived winter, producing 30–40 kg/ha nitrogen. The “Milan” strain was the most herbicide-resistant and productive	[116]
Phormidium sp.	Corn	100% seed germination	[109]
Nostoc minutum and Anabaena spiroides	broad bean	Treatment with mixtures of cyanobacteria and organic fertilizer significantly increased dry weight of broad bean more than full chemical and organic fertilizers doses by 41% and 103%, respectively	[110]
Aphanothece sp.	Tomato plant	Boosts biomass, reduces heavy metal uptake, and enhances growth, nutrient absorption, and biochemical responses	[117]

). However, large-scale adoption requires the further optimization of application methods, strain selection, and field-level validation to ensure consistent performance across diverse agroecosystems.

3.4. Cyanobacteria as Bioplastic Source

Polyhydroxyalkanoates (PHAs) are neutral lipids that contain organisms, including cyanobacteria, stored intracellularly as energy reserves and carbon sources. These compounds have gained significant attention over the past three decades due to their potential as alternatives to conventional plastics. Polyhydroxybutyrate (PHB), one form of PHA, is particularly interesting due to its thermoplastic properties which are like polypropylene, but 100% biodegradable [118,119]. This combination of the functional similarity to petrochemical plastics and complete biodegradability positions PHB as a promising material for reducing plastic pollution.

Cyanobacteria have emerged as promising PHA producers due to their unique features. These photosynthetic organisms can synthesize PHAs through oxygenic photosynthesis while requiring minimal nutrients for growth. Like higher plants, they can fix atmospheric CO₂ and convert it into PHAs under nitrogen-limiting conditions [11]. Compared to heterotrophic PHA-producing bacteria, cyanobacteria offer a distinct advantage by utilizing light and CO₂ as primary resources, thereby reducing the reliance on organic carbon substrates and lowering production costs. The resulting PHAs can be completely mineralized into water and carbon dioxide by naturally occurring microorganisms, making them ideal biodegradable materials [11,120].

Research has examined PHB accumulation in cyanobacterial strains under different conditions (Table 6). Under normal photoautotrophic conditions, PHB levels typically remain below 9% of dry weight. However, nutrient stress conditions, particularly nitrogen or phosphate deprivation, can significantly enhance PHB accumulation. For instance, nitrogen deprivation increased the PHB content in Synechococcus sp. to 27% of dry weight, while phosphate limitation led to a 23% PHB accumulation in Nostoc muscorum [121]. In comparison, nitrogen limitation appears to be a more effective trigger for PHB accumulation across multiple strains, suggesting a common metabolic response linked to carbon flux redirection under nutrient stress. A broader screening of 137 cyanobacterial strains confirmed this trend, with nitrogen deprivation yielding increased PHB production in 63 strains [122]. This variability among strains highlights the importance of species selection and optimization strategies for maximizing the bioplastic yield.

For large-scale production, cyanobacterial PHB cultivation systems mirror those used for algal biofuels and other commodity products, primarily utilizing either open or closed cultivation systems [123]. While many wild-type and genetically modified cyanobacteria demonstrate PHB accumulation under optimized laboratory conditions, large-scale production studies remain limited [124]. This gap between laboratory-scale success and industrial implementation represents a major challenge for commercialization. Notably, Spirulina strain LEB 18 achieved a biopolymer content of 44% when cultivated in a photobioreactor [125]. Compared to typical yields under standard conditions, this result demonstrates the potential for significantly enhanced production through controlled cultivation systems and strain optimization.

Overall, a comparative synthesis indicates that cyanobacteria offer a sustainable and versatile platform for bioplastic production, combining carbon capture, low nutrient requirements, and biodegradability. However, challenges related to low baseline yields, strain variability, and scalability must be addressed through metabolic engineering, process optimization, and reactor design improvements to enable economically viable large-scale production.

Table 6. PHB accumulation in different cyanobacterial strains under various culture conditions.

Cyanobacterial Strains	PHB Content (% DCW)	Substrate and Culture Conditions	PHA Composition	References
Nostoc muscorum Agardh	60	Acetate and valerate, N deficiency	PHB	[126]
Nostoc muscorum	22	CO2, P starvation	PHB	[127]
Synechococcus elongates	17.2	CO2, sucrose, N deficiency	Not specified	[128]
Synechococcus sp.	1	CO2	PHB	[129]
Synechococcus sp.	~4.5	Light, CO2 (photoautotrophy)	P (3HB-co-4HV)	[130]
Microcystis aeruginosa	0.0721	Urea, 24 h light	PHB	[131]
Oscillatoria agardhii	0.0006	NaNO3, 24 h light	PHB	[132]
Spirulina	7	NaNO3, 24 h light	PHB	[132]
Spirulina	3	NaNO3, 24 h light	PHA	[132]
Anabaena constricta	0.01495	N deficiency, 24 h light	PHB	[132]
Microcystis aeruginosa	0.04–0.05	NaNO3, domestic wastewater	PHB	[132]
Anabaena sp.	2.3	NaNO3, photoautotrophic	PHB	[133]
Oscillatoria jasorvensis	15.7	Photoautotrophic, N deficiency	PHB	[133]
Spirulina platensis	10.2	NaNO3, photoautotrophic (open raceways)	PHB	[133]
Gleocapsa gelatinosa	5.6	NaNO3, photoautotrophic	PHB	[121]
Phormidium sp.	14	Photoautotrophic (in flask), N limitation	PHB	[134]

Table 6. PHB accumulation in different cyanobacterial strains under various culture conditions.

Cyanobacterial Strains	PHB Content (% DCW)	Substrate and Culture Conditions	PHA Composition	References
Nostoc muscorum Agardh	60	Acetate and valerate, N deficiency	PHB	[126]
Nostoc muscorum	22	CO2, P starvation	PHB	[127]
Synechococcus elongates	17.2	CO2, sucrose, N deficiency	Not specified	[128]
Synechococcus sp.	1	CO2	PHB	[129]
Synechococcus sp.	~4.5	Light, CO2 (photoautotrophy)	P (3HB-co-4HV)	[130]
Microcystis aeruginosa	0.0721	Urea, 24 h light	PHB	[131]
Oscillatoria agardhii	0.0006	NaNO3, 24 h light	PHB	[132]
Spirulina	7	NaNO3, 24 h light	PHB	[132]
Spirulina	3	NaNO3, 24 h light	PHA	[132]
Anabaena constricta	0.01495	N deficiency, 24 h light	PHB	[132]
Microcystis aeruginosa	0.04–0.05	NaNO3, domestic wastewater	PHB	[132]
Anabaena sp.	2.3	NaNO3, photoautotrophic	PHB	[133]
Oscillatoria jasorvensis	15.7	Photoautotrophic, N deficiency	PHB	[133]
Spirulina platensis	10.2	NaNO3, photoautotrophic (open raceways)	PHB	[133]
Gleocapsa gelatinosa	5.6	NaNO3, photoautotrophic	PHB	[121]
Phormidium sp.	14	Photoautotrophic (in flask), N limitation	PHB	[134]

3.5. Ecological Applications of Cyanobacteria

The use of beneficial cyanobacteria presents an environmentally friendly alternative to conventional management practices. Cyanobacterial communities can enhance soil microbiota diversity while simultaneously improving soil conditions. Compared to traditional agricultural inputs, cyanobacteria provide a nature-based solution that integrates soil restoration with ecosystem sustainability. This approach can reduce crop production expenses when integrated with sustainable agricultural practices such as crop rotation, organic fertilization, reduced tillage, and biological pest control methods [135]. In photosynthetic environments where nitrogen is limited, particularly those lacking nitrate and ammonium, cyanobacteria serve as the primary nitrogen-fixing organisms [136]. These diazotrophic cyanobacteria have developed various complex mechanisms to shield their nitrogenase enzyme from oxygen exposure, both from external sources and internal production [137]. They primarily achieve this through either the spatial or temporal separation of processes, or by combining both approaches [137]. This adaptive capability distinguishes cyanobacteria from many other microorganisms, enabling them to maintain nitrogen fixation under fluctuating environmental conditions.

Research has demonstrated significant ecological benefits of cyanobacteria in diverse environments. In the desert soils of Dalateqi county in Inner Mongolia where the organic carbon and total nitrogen levels are low, the occurrence of cyanobacterial species Microcoleus vaginatus Gom and Scytonema javanicum Born et Flah resulted in a five-fold increase in soil fertility [138]. In a similar study in the semi-arid region of Hisar, India, it was observed that the cyanobacterial species Anabaena doliolum, Cylindrospermum sphaerica, and Nostoc calcicola stimulated carbon and nitrogen mineralization and did so by enhancing soil microbial activity [139]. In comparison, these studies collectively demonstrate that cyanobacteria act as ecosystem engineers, improving nutrient cycling and soil fertility across both desert and semi-arid systems.

Cyanobacteria also serve as pioneer microorganisms in dry ecosystems, as they are the first organisms to colonize land, thereby facilitating the transition of other microbial communities and diversifying the microbial diversity [140]. This role in ecological succession highlights their importance not only in soil improvement but also in long-term ecosystem development and resilience. They also assist with ecological succession, as the species provide other types of associations and patterns of nutrient exchange.

Cyanobacteria further contribute significantly to reductions in methane emissions, which is an important environmental concern. Methane (CH₄) is a potent greenhouse gas with approximately 20 times the impact of CO₂ [141]. In the initial two decades following emission, CH₄ demonstrates roughly 80 times the greenhouse warming potential of CO₂, although it has a shorter atmospheric residence time [141]. With projected increases in the human population, subsequent food demand, waste production, and fossil fuel consumption, atmospheric CH₄ concentrations are expected to rise further [135]. Therefore, this situation necessitates environmentally sustainable solutions for methane mitigation.

Cyanobacteria show promising potential in addressing global warming challenges caused by anthropogenic greenhouse gas emissions [135]. This is particularly relevant in rice cultivation, which, despite being a crucial global food source, significantly contributes to global warming through methane emissions [142]. A microcosm demonstrated that inoculating rice soil with two cyanobacterial species, Calothrix and Nostoc, reduced CH4 emissions by a factor of 20 [141]. However, the microbial responses varied between the strains; Calothrix stimulated Type Ia methanotrophs in the surface layer, enhancing CH4 oxidation, while Nostoc reduced the methanogen abundance in the subsurface layer and increased the pmoA transcripts of Type Ib methanotrophs. This means that the effectiveness of cyanobacterial inoculants for CH4 mitigation is determined by the specific pairing of cyanobacteria with methane-cycling microbes and their ecological traits [141]. This comparison reveals that cyanobacterial species influence methane cycling through distinct ecological pathways, emphasizing the importance of species-specific interactions with microbial communities.

Another study documented that the cyanobacterial species Synechocystis was the species that most effectively reduced the methane concentration by 10–20-fold higher than controls without cyanobacteria, such that the mitigation effect was dependent on the availability of light and was unnoticeable in nonsterile soils incubated in the dark [142]. The same study also showed that soil treated with a combined application of urea, a cyanobacterial mixture, and Azolla microphylla had methane oxidation activity that was more rapid than soils treated with urea only, regardless of the nitrogen application rate [142]. In comparison to single-input systems, these integrated approaches demonstrate synergistic effects, suggesting that combining cyanobacteria with other biological or chemical inputs can significantly enhance the methane mitigation efficiency.

Overall, a comparative synthesis indicates that cyanobacteria play multifunctional ecological roles, including soil restoration, nutrient cycling, ecosystem succession, and greenhouse gas mitigation. While their effectiveness varies depending on the species, environmental conditions, and microbial interactions, their ability to operate across multiple ecological processes positions them as key agents in sustainable environmental management. However, further field-scale studies and ecosystem-specific optimization are required to fully harness their ecological potential.

4. Research Gaps and Future Directions

Despite the growing body of research on cyanobacteria from the Arabian Peninsula, several critical gaps remain that limit the translation of laboratory findings into practical and scalable applications. A major limitation across studies is the lack of standardization in experimental methodologies, including cultivation conditions, extraction techniques, and analytical approaches. This variability makes the direct comparison between studies difficult and often leads to inconsistent conclusions regarding the metabolite yield, bioactivity, and functional performance.

Another key gap lies in the limited understanding of species-specific variability. While numerous cyanobacterial strains have been identified, their metabolic pathways, environmental adaptability, and productivity under different conditions are not comprehensively characterized. This is particularly important given that many applications—such as biohydrogen production, bioplastic synthesis, and therapeutic compound extraction—are highly dependent on strain selection and optimization.

In addition, most studies remain confined to laboratory-scale experiments, with relatively few investigations addressing pilot-scale or industrial-scale implementation. Challenges such as low productivity, oxygen sensitivity (in the case of biohydrogen production), and economic feasibility have not been sufficiently resolved. Similarly, while bioremediation and biofertilization applications show promising results under controlled conditions, their long-term effectiveness and stability under field conditions remain underexplored.

For therapeutic applications, although a wide range of bioactive compounds has been identified, there is a lack of in vivo studies, clinical validation, and toxicity assessments. This gap limits the translation of cyanobacterial metabolites into pharmaceutical or nutraceutical products. Furthermore, the influence of environmental stressors on metabolite expression and bioactivity is not fully understood, which may affect reproducibility and scalability.

Future research should therefore prioritize the development of standardized protocols for cultivation, extraction, and characterization to enable a reliable comparison across studies. Advanced approaches such as metabolic engineering, omics technologies, and synthetic biology should be employed to enhance metabolite production and optimize strain performance. Additionally, scaling up production systems—particularly through improved photobioreactor design and integration with existing industrial processes—will be essential for commercial viability.

There is also a need to develop integrated and multifunctional systems that combine multiple applications, such as coupling wastewater treatment with biomass production or linking biohydrogen generation with carbon capture. Such approaches can improve the overall process efficiency and economic feasibility. Field-scale validation and long-term ecological assessments are equally important to ensure the sustainability and robustness of these applications under real environmental conditions.

The future of microalgae research in the Arabian Peninsula is to be considered as part of its unique political diversity (seven countries with vastly different levels of capacity for conducting research), economic diversity (Gulf States that are rich in oil versus Yemen, which has been affected by war), and unique environmental conditions (extreme arid conditions, high salinity, and limited access to fresh water) [143,144,145]. The most important research areas will be as follows: (1) establishing an integrated regional molecular barcode-based biodiversity database; (2) developing cost-effective cultivation systems to support algal cultivation in poor or underdeveloped regions; (3) the investigation of halophilic/thermophilic species for use in generating renewable energy through bio-energy production and bioremediation; (4) the development of networks across borders; and (5) integrating algae biotechnology into existing circular economies and water security frameworks [146].

Overall, addressing these research gaps will be crucial for unlocking the full potential of cyanobacteria as sustainable bioresources in the Arabian Peninsula. A coordinated effort integrating fundamental research, technological innovation, and applied studies is required to bridge the gap between laboratory discoveries and real-world implementation.

5. Conclusions

The comprehensive review of cyanobacterial species from the Arabian Peninsula illustrates their exceptional potential as biological resources for addressing a range of technological, environmental, and agricultural challenges. Their diverse metabolic capabilities expand their uses from therapeutic products to environmental solutions. Noteworthy applications include biohydrogen generation, biofertilization for sustainable agriculture, the bioremediation of pollutants and heavy metals, and the evolving roles in bioplastic production through polyhydroxyalkanoate synthesis. Their role in the environment is extraordinary in terms of mitigating methane and soil microbial enhancers, providing natural solutions to tackle environmental issues. The unique harsh environmental characteristics of the Arabian Peninsula could potentially allow the evolution of resilient and metabolically adaptable cyanobacterial strains that would make them well-suited for biotechnological applications under extreme conditions. A comparative analysis of the reviewed studies indicates that, while some functions are widely conserved across species, others are highly species- and condition-dependent, highlighting the need for targeted strain selection. The investigation and utilization of these microorganisms are very important, given the continuously growing global challenges related to energy security, environmental contamination, and sustainable agriculture. The future research direction should also include optimizing growth conditions, enhancing the number of compounds yielded, and developing a more effective use of these multifunctional microorganisms across several sectors in the Arabian Peninsula region.