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Review

Toward Sustainable Polyhydroxyalkanoates: A Next-Gen Biotechnology Approach

by
Vipin Chandra Kalia
1,
Rahul Vikram Singh
1,
Chunjie Gong
2 and
Jung-Kul Lee
1,*
1
Department of Chemical Engineering, Konkuk University, 120 Neungdong-ro, Gwangjin-gu, Seoul 05029, Republic of Korea
2
Cooperative Innovation Center of Industrial Fermentation (Ministry of Education & Hubei Province), Key Laboratory of Fermentation Engineering (Ministry of Education), National “111” Center for Cellular Regulation and Molecular Pharmaceutics, Hubei University of Technology, Wuhan 430068, China
*
Author to whom correspondence should be addressed.
Polymers 2025, 17(7), 853; https://doi.org/10.3390/polym17070853
Submission received: 28 February 2025 / Revised: 19 March 2025 / Accepted: 20 March 2025 / Published: 22 March 2025
(This article belongs to the Section Biobased and Biodegradable Polymers)
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Abstract

:
Polyhydroxyalkanoates (PHAs) are biodegradable biopolymers synthesized by microorganisms and serve as sustainable alternatives to petroleum-based plastics. While traditional PHA production relies on refined carbon sources and pure cultures, high costs and scalability challenges limit commercial viability. Extremophiles, particularly halophiles, have emerged as promising candidates for cost-effective, large-scale production of PHAs. Their ability to thrive in extreme environments reduces contamination risks, minimizes the need for sterilization, and lowers operational costs. Advancements in metabolic engineering, synthetic biology, and CRISPR-based genome editing have enhanced PHA yields by optimizing metabolic flux and cell morphology. Additionally, utilizing alternative feedstocks such as biowaste, syngas, methane, and CO₂ improves economic feasibility. Next-generation industrial biotechnology integrates extremophilic microbes with AI-driven fermentation and eco-friendly downstream processing to enhance scalability. Industrial-scale production of PHAs using Halomonas spp. and other extremophiles demonstrates significant progress toward commercialization, paving the way for sustainable biopolymer applications in reducing plastic pollution

1. Introduction

Polyhydroxyalkanoates (PHAs) are biodegradable polyesters synthesized by microorganisms as intracellular storage compounds, primarily under environmental stress [1]. The ability of bacteria to withstand stress plays a crucial role in determining their suitability for PHA production. Among the different types of PHA, poly(3-hydroxybutyrate) (PHB) and its copolymers with 3-hydroxyvalerate (3HV) or other monomers significantly influence the material properties, making them suitable for various industrial applications: (i) 3-Hydroxybutyrate (3HB) [CH3−CH(OH)−CH2−COO−] forms poly(3-hydroxybutyrate) (PHB), which is highly crystalline and brittle; (ii) 3-Hydroxyvalerate (3HV) [CH3−CH2−CH(OH)−CH2−COO−] is a monomer that reduces crystallinity when incorporated into PHB, improving flexibility and toughness and improving mechanical properties; and (iii) poly(3-hydroxybutyrate-3-hydroxyvalerate (P(3HB-3HV) is a copolymer of PHB and 3HV. The percentage of 3HV (XX mol%) affects polymer properties: (i) higher 3HV content → more flexible, lower melting point, better processability, and (ii) lower 3HV content → stiffer and more brittle, but higher strength. To produce PHBV, a precursor such as propionic acid or valeric acid is fed to microbial culture. These precursors are converted into 3HV units, which in turn influence the copolymer composition (XX mol% 3HV). By adjusting XX mol% 3HV and M.Wt., the polymer’s flexibility, thermal stability, and degradation rate can be fine-tuned. Higher molecular weight results in better mechanical strength, whereas increased 3HV content improves flexibility and reduces brittleness [2].
Halophiles and thermophiles offer distinct advantages over mesophiles due to their unique adaptability and physiological traits. Halophiles thrive in high-salinity environments, thereby reducing contamination risks and minimizing the need for sterilization. High salt concentrations facilitate easy PHA extraction, and their salt tolerance allows cultivation in open or semi-open systems, further reducing operational expenses. Thermophiles, thriving at 50–80 °C, enhance substrate solubility, oxygen transfer, and metabolic activity, leading to higher PHA productivity. Their high growth rates reduce fermentation time, and their contaminant resistance simplifies sterilization. Thermophiles also support continuous bioprocessing [3,4,5,6]. Combining halophilic and thermophilic traits could optimize industrial PHA production by enhancing efficiency and reducing costs. Halophiles may be preferable due to their ability to reduce contamination risks without the high energy input required for thermophilic growth. Their open-system cultivation and simple PHA extraction make them more cost-effective. However, thermophiles provide advantages in continuous fermentation and metabolic efficiency. The choice depends on process requirements, but halophiles generally offer greater economic feasibility in large-scale PHA production. These extremophiles offer multiple advantages for sustainable PHA production, most notably by reducing the risk of microbial contamination, which can cause significant economic losses. This forms the conceptual foundation of “Next-Generation Industrial Biotechnology” (NGIB) (Figure 1). It integrates metabolic engineering and synthetic biology to develop cost-effective and sustainable bioprocesses that compete with conventional petroleum-based plastics [7]. Traditional PHA production relies on pure microbial cultures grown on refined carbon sources such as glucose or saccharose. A significant drawback of this approach is the high feedstock cost, which accounts for approximately 40% of total production expenses [8]. Alternative strategies, including biowaste as a cost-effective carbon source, have been explored to mitigate high feed costs. The use of biowastes as feed was successfully demonstrated using heterotrophic microbes [9,10]. In addition to organic substrates, PHA production can leverage inorganic carbon sources such as CO2. Photoautotrophic microorganisms, including cyanobacteria, use CO2 as a carbon source [11]. Other microbes, such as Rhodospirillum rubrum, can metabolize syngas (a mixture of CO, CO2, and H2) for PHA biosynthesis [12]. Methane (CH4) from biogas and natural gas has been identified as a viable substrate for methylotrophic bacteria [13]. Another promising alternative to conventional PHA production is the use of well-defined microbial consortia rather than pure cultures, as this approach eliminates the need for sterilizing the apparatus and medium, and significantly reduces production costs [14]. Using well-defined microbial consortia for PHA production presents several advantages over pure cultures, particularly in reducing sterilization requirements and overall production costs. In traditional PHA production, maintaining pure cultures requires stringent sterile conditions, including the sterilization of apparatus, medium, and bioreactors, which significantly increase energy consumption and operational expenses. In contrast, microbial consortia, composed of naturally coexisting or engineered microbial communities, can outcompete contaminants and function efficiently in nonsterile environments, eliminating the need for costly sterilization processes. Additionally, consortia facilitate efficient substrate utilization by enabling the division of labor among microbial species, leading to improved carbon source conversion and higher PHA yields [6]. They also enhance process resilience by maintaining stability under fluctuating conditions, reducing the risk of culture failure. By leveraging metabolic complementarities and adaptive capabilities, microbial consortia provide a robust and economically viable alternative for large-scale, sustainable PHA production, aligning with NGIB principles. To overcome the limitations of the traditional methods, researchers have proposed NGIB as a novel strategy for cost-effective and sustainable PHA biosynthesis. This concept focuses on utilizing extremophilic microbes as robust microbial chassis for industrial bioprocesses [15,16,17]. PHA production by extremophiles, particularly halophiles, and thermophiles, offers significant advantages as they thrive in extreme environments that naturally suppress microbial contamination, thereby reducing the need for stringent sterilization protocols [4]. This review emphasizes the research efforts that highlight the potential of halophilic microbes in the development of scalable and sustainable PHA production systems. Future efforts should continue to optimize the metabolic pathways and bioprocess conditions to enhance the feasibility of industrial-scale implementation.

2. Current Status of Industrial Biotechnology

PHAs are biopolymers synthesized by various microbes and have garnered significant interest because of their biodegradability and potential as sustainable alternatives to petroleum-based plastics. In Halomonas, the primary biosynthetic pathway leading to scl-PHA synthesis involves the condensation of two acetyl-CoA molecules by 3-ketoacyl-CoA synthase (PhaA). The resultant acetoacetyl-CoA is then reduced by acetoacetyl-CoA reductase (PhaB) using NAD(P)H. The R-3-hydroxybutyryl-CoA produced in the second step is polymerized into P(3HB) by PHA synthase. For mcl-PHA synthesis, 3-hydroxy acyl-CoA precursors are derived from fatty acid de novo synthesis or β-oxidation of fatty acids [6]. PHA production involves multiple stages, including microbial screening, strain improvement, laboratory-scale optimization, and large-scale industrial implementation. Despite advancements in genetic engineering and industrial biotechnology, several challenges persist, particularly in terms of production costs and scalability [18]. The initial step in PHA production involves identifying microbial strains capable of efficiently synthesizing PHAs. Wild-type bacterial strains were first used, followed by genetic engineering to enhance production. The production of short-chain-length polyhydroxyalkanoates (scl-PHA) was successfully demonstrated using Ralstonia eutropha and Alcaligenes latus [19]. Additionally, copolymers such as poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) have been synthesized using Aeromonas hydrophila and R. eutropha [14,20]. Various species of Pseudomonas produce medium-chain-length PHA (mcl-PHA). Enhancing production through strain improvement has been achieved by deleting genes involved in the β-oxidation pathway. This genetic modification enables Pseudomonas spp. to maintain their chain length and structure, producing homopolymers, copolymers, and functionally modified PHAs through the selective addition of fatty acids [21]. Escherichia coli, which does not naturally produce PHAs, has been engineered to become a hyperproducer of various PHA types [22,23]. E. coli, despite its inability to naturally synthesize PHAs, has been extensively engineered to become a next-generation microbial chassis for PHA production due to its well-characterized genetics, rapid growth rate, and ease of genetic manipulation. Key PHA biosynthetic pathways have been successfully introduced into E. coli through metabolic engineering, enabling the production of PHA copolymers. Advanced genetic tools, such as CRISPR/Cas9, synthetic biology, and metabolic flux optimization, have further enhanced E. coli’s PHA production capacity by improving precursor supply, balancing redox states, and eliminating competing pathways. Advances in industrial biotechnology have enabled E. coli and R. eutropha to achieve high cell densities and productivity, reaching dry biomass levels of 232 g/L and productivity of 4.63 g/L/h, particularly when recombinant E. coli was engineered using the phaCAB operon from A. latus [24,25,26]. Despite advancements in strain engineering and bioprocess optimization, several limitations remain. High production costs, ranging from USD 4 to 6 per kg, make PHAs less competitive than fossil-fuel-derived plastics [27,28,29]. The key challenges include expensive sterilization processes, prevention of contamination, low feed-to-PHA conversion ratios, and high energy consumption for aeration. Additionally, the reliance on glucose as the primary feedstock presents economic and environmental concerns, including substantial water usage and costly downstream processing requirements [17]. Future research should focus on overcoming the challenges related to fermentation technology, alternative feedstock utilization, and cost-effective downstream processing methods, which are crucial for achieving commercially viable PHA production.

3. Next-Generation Industrial Biotechnology

The effort to enhance industrial-scale PHA production has increasingly focused on utilizing extremophiles. These microorganisms can thrive under harsh physiological conditions that are inhospitable to most bacteria, making them ideal candidates for bioprocessing [30,31,32,33,34,35,36,37,38]. By leveraging extremophiles, PHA production can be made more sustainable and cost-effective. The ability of extremophiles to withstand high temperatures and salinity significantly restricts microbial contamination, thereby reducing the need for sterilization and minimizing energy consumption [39,40,41,42,43]. This selective growth advantage allows for more controlled and efficient fermentation. Industrial PHA production incorporates continuous culture, low-energy processing, and automated control systems to enhance its efficiency. These measures reduce operational costs while improving yield and quality [15,17,44]. Economic and environmental sustainability are being addressed through the use of alternative feedstocks, including hydrolysates of cellulosic materials, pretreated sludge, kitchen waste, and syngas [45]. Substituting freshwater with seawater or treated wastewater is a cost-effective and sustainable solution for PHA production. High-temperature and high-salinity conditions reduce the need for sterilization and lower energy requirements. Traditional stainless-steel fermenters may also be replaced by more cost-effective materials, such as ceramics, plastics, or cement, making PHA production more economically viable. Extremophiles and recombinant bacteria serve as an efficient biological chassis for the optimized synthesis of biopolymers [15,30,46].

4. PHA Production by Halophilic Archaea

Among the various microorganisms known to accumulate PHAs under hypersaline conditions, a few notable examples include archaea such as Haloarcula sp., Haloferax sp., Halogeometricum sp., Halopiger sp., and Natrinema sp.

4.1. PHA Production from Pure Sugars

Initial studies on PHA production by archaeal species used pure sugars as feed under highly saline conditions. A study by Han et al. demonstrated that Haloarcula marismortui accumulates poly(3-hydroxybutyrate) [P(3HB)] up to 21% of its cell dry weight (CDW) when grown on glucose and 20% NaCl under shake-flask conditions [47]. Haloferax mediterranei fermented glucose and yeast extract to accumulate P(3HB-3HV) in a fed-batch culture. After 117 h, the PHA yield reached 41.69 g/L. The resulting copolymers had two distinct molecular weight (M.Wt.) distributions: (i) 93.4 wt% with 10.7 mol% 3HV and M.Wt. of 569.5 kg/mol and (ii) 6.6 wt% with 12.3 mol% 3HV and M.Wt. of 78.2 kg/mol [48]. H. mediterranei CGMCC 1.2087 synthesized P(3HB-3HV) up to 24% and 18% (wt/wt) in limited and nutrient-rich media, respectively, with 1% starch as the carbon source [49]. The archaeon Halogranum amylolyticum TNN58 synthesizes P(3HB-3HV) with a 3HV content of 20.1 mol% when cultivated with glucose as the carbon source. Process optimization, especially medium and culture conditions, enabled an 8-fold increase in PHBV production and a 4-fold increase in CDW in a fed-batch process compared to a batch process, making it a strong candidate for large-scale PHA production [50]. Halogeometricum borinquense strain E3, an extremely halophilic archaeon, achieved PHA accumulation up to 73.51% when supplemented with 2% glucose. Adding a precursor enabled the biosynthesis of P(3HB-3HV) containing 21.47 mol% 3HV [51]. Another extremophilic archaeon, Natrinema ajinwuensis RM-G10, demonstrated PHA accumulation of 61.02% with a 3HV content of 13.93 mol% when grown under optimized conditions [52].

4.2. PHA Production from Biowastes

PHA production by halophiles using starch-based feedstock carbon sources has been reported previously (Table 1). H. mediterranei accumulated 50.8% P(3HB-3HV) of CDW from extruded starch under high salt concentrations during fed-batch fermentation [53]. Using extruded rice bran and corn starch (1:8 g/g) as carbon sources, H. mediterranei achieved a PHA yield of 77.8 g/L in a 5 L repeated fed-batch fermenter, with sustained long-term production under hypersaline conditions [54]. Natrinema sp. strain 1KYS1 accumulated 0.055 and 0.075 g/L PHA when grown on starch and corn starch, respectively [46]. Dairy and ethanol industry waste has been used as a cheaper feedstock for H. mediterranei DSM 1411, which produces 50% P(3HB-3HV) from hydrolyzed whey, even without precursors. In contrast, Pseudomonas hydrogenovora and Hydrogenophaga pseudoflava required valeric acid supplementation to yield comparable copolymers [55]. The same strain synthesized (i) 72.8% P(3HB-3HV) (6 mol% 3HV) from sugars from hydrolyzed whey and (ii) 87.5% PHA terpolyester (21.8 mol%-3HV and 5.1 mol%-4HB) from precursor-supplemented whey sugars [56]. H. mediterranei DSM 1411 used vinasse (ethanol industry waste) pretreated with activated carbon (25–50% v/v) to yield 13.79 g/L PHA while simultaneously reducing pollution, biological oxygen demand (BOD5) by 78%, and chemical oxygen demand by 80% [57]. Further studies on rice-based ethanol waste resulted in 71% P(3HB-3HV) (15.4 mol% 3HV) of CDW, with an 83% pollution load reduction and 96% recovery of medium salts, enhancing the industrial feasibility of the process [58]. H. marismortui metabolized 10% raw vinasse into 2.8 g/L P(3HB) in shake flasks, whereas activated carbon 100% pretreated vinasse led to 4.5 g /L P(3HB) [59]. Natrinema sp. strain 1KYS1 accumulated 0.091 g/L PHA, when grown on whey [46]. In addition, PHA production by Haloarchaea has been reported in agro-industrial waste and other feedstocks. Natrinema sp. strain 1KYS1 was reported to have the potential to accumulate 0.039, 0.046, and 0.077 g/L PHA in CDW when grown on apple waste, melon waste, and tomato waste, respectively [46]. Phenolic compounds are inhibitory to bacterial growth. H. mediterranei used 15% olive mill wastewater as feedstock at 22% salt concentration, yielding 0.2 g/L PHA with a 43% CDW content. Without precursor supplementation, P(3HB-3HV) had 6.5 mol% 3HV, with lower melting points (140.1 °C and 154.4 °C) compared to pure P(3HB), eliminating the need for costly dephenolization [60]. H. borinquense strain E3 utilized sugarcane bagasse (SCB) hydrolysate to produce (i) 50.4% P(3HB-3HV) (13.29 mol% 3HV) from 25% SCB hydrolysate, and (ii) 45.7% P(3HB-3HV) from 50% SCB hydrolysate [61]. The same strain metabolized cassava waste and starch to yield (i) P(3HB-3HV) (13.11 mol% 3HV) at 4.6 g/L from starch, and (ii) P(3HB-3HV) (19.65 mol% 3HV) at 1.52 g/L from cassava waste, addressing environmental concerns related to industrial cassava discharge [62].
Haloarchaea, particularly H. mediterranei, offers a sustainable and cost-effective approach for PHA production by utilizing diverse low-cost feedstocks. Their ability to thrive in high-salt environments eliminates the need for stringent sterilization, which can potentially reduce production costs. However, environmental concerns regarding salt disposal must be addressed, as the discharged effluent often contains total dissolved solids above 2000 mg/L [58]. Future research should focus on optimizing bioprocessing conditions and developing salt recovery strategies to enhance industrial feasibility.

5. PHA Production by Halophilic Bacteria

Among halophiles, several bacterial genera, including Halomonas, Oceanimonas, Salinivibrio, Bacillus, and Vibrio spp. have been extensively studied for PHA production.

5.1. PHA Production from Sugars

P(3HB) was produced by alkalophilic and halophilic Halomonas sp. KM-1 under non-sterile batch culture conditions. The fermentation yielded 7.97 g/L PHB after 24 h in a 5% glucose medium. Increasing glucose concentration to 10% enhanced P(3HB) yield to 26.3 g/L at 36 h. In contrast, Halomonas sp. O-1 produced only 2.13 g/L P(3HB), whereas Halomonas sp. KM-1 produced 28.34 g/L, demonstrating strain-dependent genetic variability [63]. Fed-batch culture studies of Halomonas boliviensis further illustrated the influence of the medium components on P(3HB) synthesis. Optimal growth conditions with NH4Cl and K2HPO4 supplementation resulted in a 5.89-fold higher cell biomass than 0.1% glutamine alone, with a resultant PHB yield of 20.7 g/L within 18 h. Further optimization using MSG, NH4Cl, and K2HPO4 at specific concentrations yielded 35.64 g/L PHB [64]. Halomonas sp. YLGW01 produced 8.65 g/L P(3HB) using fructose as the carbon source [65]. Advancements in genetic engineering have further improved PHA production. In Halomonas bluephagenesis TD01, engineering efforts targeting phasin (PhaP) genes have influenced PHA granule size. In contrast, overexpression of minC and minD genes (coding for Z-ring positioning protein) resulted in large cell sizes with PHA granules up to 10 μm, indicating a correlation between cell morphology and PHA accumulation [66]. Additionally, bacterial morphology regulation via mreB (encoding a dynamic cytoskeletal protein) and ftsZ (encoding a bacterial fission ring formation protein) was leveraged in Halomonas campaniensis LS21 using temperature-sensitive plasmids. Controlled expression at 37 °C increased PHB yield by 80% while facilitating cell harvesting and downstream processing [67]. Halophilic Halomonas profundus grows optimally at pH 8–9 and 2–3% NaCl, producing P(3HB) and P(3HB-3HV) [68]. Continuous culture studies demonstrated sustained PHA production by Halomonas TD01, achieving 24 g/L PHA in a 14-day unsterile process. Under nitrogen-limiting conditions, PHB content increased to 65–70%, but the PHA yield was lower at 13 g/L due to the medium dilution in the second fermenter [69]. Genetic modifications in Halomonas TD01, including the deletion of PHA depolymerase and overexpression of genes involved in propionic acid metabolism, yielded P(3HB-3HV) with 12 mol% 3HV [70]. Further enhancements using the LacIq-Ptrc system in Halomonas TD08 increased the PHB content from 69 to 82 wt%, facilitating downstream processing and reducing production costs [71].
Clustered regularly interspaced short palindromic repeat interference (CRISPRi) technology has been applied to Halomonas species TD01 to regulate genes such as ftsZ, prpC, and gltA. This led to elongated cell morphology, enhanced acetyl-CoA flux toward PHA synthesis, and increased P(3HB-3HV) copolymer production of up to 13 mol% 3HV [72]. Several additional Halomonas spp. have demonstrated significant PHA production capabilities under varied conditions: (i) H. elongata strains accumulated PHA at 10% NaCl with diverse carbon sources, H. elongata A1 synthesized P(3HB) at 2.59 g/L and 0.49 g/L using glucose and carboxymethyl cellulose, respectively [73,74]; (ii) H. venusta KT832796 optimized carbon-to-nitrogen ratios to achieve an 8.65-fold increase in PHA production [75]; (iii) H. cupida J9 produced short- and medium-chain-length PHAs (scl-co-mcl PHAs) from glucose and glycerol in unsterile fermentation [76]; (iv) H. pacifica ASL10 and H. salifodiane ASL11 produced P(3HB-3HV) from sucrose with yields of 6.9 g/L and 7.1 g/L at a pH of 7 and 1.7% NaCl [77]; a few other strains, such as Oceanimonas strain GK1 accumulated 75 wt% P(3HB) at 5% NaCl with sucrose and peptone as carbon and nitrogen sources [78]; (v) Salinivibrio sp. TGB10 achieved high PHB and PHBV yields from various sugars, with propionate supplementation enhancing PHBV content to 72.02 mol% 3HV [79]; and (vi) Vibrio proteolyticus strain produced 2.7 g/L PHA on M9 minimal medium supplemented with fructose (2% w/v) as carbon source in a NaCl (5% w/v). PAH copolymer P(3HB-3HV) with a 3HV content of 15.8 mol% was produced by the addition of propionate (0.3%) to the medium, even under unsterile conditions and higher NaCl concentrations [80].

5.2. PHA Production from Industrial and Agricultural Wastes

Several species of Halomonas and Bacillus have shown promising PHA production capabilities (Table 2). Halomonas campisalis MCM B-1027 produced 0.36 g/L PHA (5.6 mol% 3HV) on 1% (v/v) aqueous extract of bagasse [81]. H. halophila accumulated up to 3.26 g/L P(3HB), with NaCl concentrations regulating P(3HB) yields from hydrolysates of cheese whey, corn stover, sawdust, sugar beet, and spent coffee grounds. In contrast, with pure sugars such as cellobiose, galactose, and glucose as carbon sources, PHA yields by H. halophila were 2.59, 3.41, and 4.58 g/L [82]. Three recombinant strains (H. elongata P2) reached P(3HB) contents of 0.44 g/L, 1.28 g/L, and 1.81 g/L when cultivated on wheat straw, mixed substrates, and oleic acid, respectively [74]. Under unsterilized conditions using fructose syrup, the P(3HB) content by Halomonas sp. YLGW01 increased to 95.26%. The strain exhibited enhanced cell size (8.39 μm) compared to 2.34 μm on glucose, facilitating downstream processing and polymer recovery [65]. The halophilic bacterium Bacillus megaterium uyuni S29 metabolizes desugarized sugar beet molasses (a high-salinity effluent) to produce 10.02 g/L P(3HB) under batch cultivation, achieving a 2- to 3-fold increase in biomass [35]. B. megaterium also metabolizes desugarized sugar beet molasses, yielding 1.2 g/L P(3HB) across six cultivation cycles [83].
Halomonas TD01 was genetically modified by introducing the conjugative plasmid, pSEVA341, using the LacIq-Ptrc system to induce gene expression. The deletion of 2-methyl citrate synthase and PHA depolymerase resulted in the Halomonas TD08 strain producing P(3HB-3HV) (4–6 mol% 3HV). Overexpression of threonine synthesis and threonine dehydrogenase improved the PHA yields. The inhibition of cell division using MinCD led to 1.4-fold longer cells, enhanced PHB accumulation from 69 to 82 wt%, simplified downstream processing, and reduced production costs [71]. Halomonas sp. KM-1 successfully utilized glycerol-rich biodiesel industry waste to produce P(3HB) [84]. Halomonas desertis G11 synthesized PHA copolymer using biodiesel-derived glycerol [85]. Halomonas taeanenisis YLGW01 metabolized crude glycerol to produce P(3HB-3HV) (17 mol% 3HV). Optimization and activated carbon treatment improved PHA yields to 10.5 g/L during fed-batch fermentation [86]. Halomonas hydrothermalis (MTCC 5445) accumulates PHA using glycerol and peptone at high salt concentrations, achieving 2.61 g/L yield in shake flasks [87]. Bacillus sonorensis SM-P-1S and Halomonas hydrothermalis SM-P-3M accumulated 0.2 g/L and 0.3 g/L P(3HB), respectively, from Jatropha biodiesel byproducts, reducing production costs [88].
PHA production under extreme conditions by various Halomonas spp. has been quite successful: (i) Halomonas cupida J9 produced scl-co-mcl PHA ((3HB-3-hydroxydodecanoate, 3HDD) from glucose and glycerol under unsterile conditions, showing superior thermal and mechanical properties [76]; (ii) Halomonas alkaliantarctica synthesized P(3HB-3HV) from crude glycerol without additional precursors, demonstrating substrate-independent PHA yields [89]; and (iii) Halomonas daqingensis effectively converted crude glycerol from algal biodiesel waste residues into PHA, achieving 0.236 g/L PHA under mesophilic conditions with 5% NaCl [90]. Enhancing PHA yield with precursors and fermentation strategies: (i) Halomonas hydrothermalis synthesized P(3HB-3HV) with 50.15 mol% 3HV using valerate as the precursor; PHA yields and molecular weight declined with an increase in NaCl concentration from 40 g/L to 100 g/L [91]; and (ii) H. bluephagenesis TD40 efficiently produced P(3HB-co-4HB) in industrial-scale (1–5 m³) bioreactors under non-sterile conditions. Waste gluconate reduced feed costs by 60%, achieving 60.4 g/L PHA (13.5 mol% 4HB) within 36 h. Yield improved to 74% by decreasing waste corn steep liquor usage, reducing energy consumption during downstream processing [92]. Other halophilic bacteria, including Yangia sp. ND199 produced P(3HB-3HV) in the presence of 4.5% NaCl. The highest PHBV productivity (53.2 wt% with 2.9 mol% 3HV) was obtained on crude glycerol supplemented with yeast extract. Further enhancement (56 wt% PHA, 0.61 g/L/h productivity) was achieved using high-fructose corn syrup [93].
Advances in PHA synthesis using halophilic microorganisms have demonstrated significant potential for the sustainable production of biopolymers. Genetic modifications, efficient carbon source utilization, and process optimization have enhanced the PHA yields and reduced production costs. The ability of these microbes to grow under non-sterile, high-salinity conditions further supports their industrial scalability. Integrating waste-derived feedstocks such as crude glycerol, biodiesel byproducts, and lignocellulosic hydrolysates mitigates environmental waste and improves economic feasibility. Future research should optimize the fermentation conditions, refine downstream processing, and explore novel extremophiles for diversified PHA compositions and enhanced properties.
Table 2. Diversity of halophilic bacteria to produce polyhydroxyalkanoates.
Table 2. Diversity of halophilic bacteria to produce polyhydroxyalkanoates.
PHA ProducerSubstrate
(%)		Salt (NaCl)
(%)		Reactor ConditionCell Dry Mass
(g/L)		Polyhydroxyalkanoate (PHA)References
Composition (%mol Copolymer)Content (wt%)Yield
(g/L)
Pure Sugars
Halomonas sp. KM-1Glucose (10)0.1Batch38.4P(3HB)73.728.34[63]
Halomonas sp. O-1Glucose (10)0.1Batch6.9P(3HB)312.13[63]
Halomonas boliviensisGlucose (2)4.5Shake flask (Fed-batch)44P(3HB)8135.4[64]
Halomonas bluephagenesis TD01Glucose (3)5Shake flask12.88P(3HB)76.169.81[66]
Halomonas campaniensis LS21Glucose (1.5)4Shake flask27P(3HB)308.1[67]
Halomonas profundus AT1214Glucose (1)2.72-stage batch (5 L)-P(3HB)-0.27[68]
Glucose a (1)2.72-stage batch (5 L)-P(3HB-3HV)
[28 mol% 3HV]		-0.27
Halomonas sp. TD01Glucose (3)6Continuous culture40P(3HB)6024[69]
Glucose (3)6Continuous culture (500 L)112P(3HB)7078.4[66]
Glucose a (3)6Continuous culture (500 L)80P(3HB-3HV) a
[12 mol% 3HV]		7056[70]
Glucose (3)6Shake flask10.22P(3HB)77.687.94[72]
Halomonas sp. TD08 pSEVA341)
(blank vector)		Glucose6Shake flask8.61P(3HB-3HV)
[trace 3HV]		70.456.05[71]
Halomonas sp. TD-gltA2 (Rec.)Glucose (3)6Shake flask13.53P(3HB)71.779.71[72]
Halomonas halophila CCM 3662Glucose (2)6.6Shake flask5.62P(3HB)81.54.58[82]
Cellobiose (2)6.6Shake flask2.86P(3HB)90.82.59
Galactose (2)6.6Shake flask4.22P(3HB)80.73.41
Halomonas elongata 2FFGlucose (1)10Shake flask-NRP(3HB)-NR0.4[73]
H. elongata A1Glucose (1)5Shake flask6.75P(3HB)22.812.59[74]
Cellulose (1)5Shake flask4.17P(3HB)11.800.49
Halomonas venusta KT832796Glucose (2)1.5Single pulse feeding37.9P(3HB)88.1233.4 (8.65-fold)[75]
Glucose (2) b1.5Fed-batch (2 L)3.52P(3HB)70.562.48
Halomonas cupida J9Glucose a8Shake flask5.5P(3HB-3HDD)321.76[76]
Halomonas pacifica ASL10Sucrose (2) + Ammonium sulphate (0.2)(up to 170)Shake flask9.59P(3HB-3HV)71.96.9[77]
Halomonas salifodiane ASL11Sucrose (2) + Ammonium sulfate (0.2)(up to 170)Shake flask8.86P(3HB-3HV)80.17.1[77]
Vibrio proteolyticusFructose (2)5Shake flask4.94P(3HB)54.72.7[80]
Fructose a (2)5Shake flask3.62P(3HB-3HV) [15.8 mol% 3HV]47.681.73
Industrial and Agricultural Wastes
Halomonas campisalis MCM B-1027Bagasse (1)4.5Shake flask0.78P(3HB-3HV)
[5.6 mol% 3HV]		46.50.36[81]
Banana peel (1)4.5Shake flask0.53P(3HB-3HV)
[52.04 mol% 3HV]		10.50.37
Orange peel (1)4.5Shake flask0.92P(3HB-3HV)
[52.04 mol% 3HV]		21.50.19
H. halophila CCM 3662Cheese whey hydrolysate6.6Shake flask8.50P(3HB)38.323.26[82]
Molasses6.6Shake flask4.05P(3HB)64.062.57
H. elongata P2Wheat straw5Shake flask8.42P(3HB)5.190.44[74]
Mixed substrates5Shake flask7.76P(3HB)16.491.28
Oleic acid5Shake flask5.76P(3HB)27.421.81
Halomonas sp. YLGW01Fructose syrup (2)2Shake flask9.15P(3HB)94.628.65[66]
Bacillus megaterium uyuni S29Sugar beet molasses (1)1Shake flask16.7P(3HB)6010.02[35]
Sugar beet molasses (5)0/5Pilot scale (500 L)20.4P(3HB)58.812[83]
Halomonas TD08 (pSEVA341-thrACBilvA) cGlycerol6Shake flask6.65P(3HB-3HV)
[6.12 mol% 3HV]		67.144.46[71]
Halomonas sp. KM-1Pure glycerol (2)-Shake flask4.69P(3HB)40.51.9[84]
Halomonas sp. KM-1Pure glycerol (5)-Shake flask5.13P(3HB)44.82,3[84]
Halomonas sp. KM-1Waste glycerol (3)-Shake flask4.10P(3HB)39.01.6[84]
Halomonas desertis G11Glycerol (1)5Shake flask2.29P(3HB-3HV)
[52 mol% 3HV]		681.54[57]
Halomonas cupida J9Glycerol10Shake flask3.5P(3HB-3HDD)291.01[76]
Halomonas sp. YLGW01Glycerol (2)2Shake flask17.5P(3HB-3HV) [13 mol% 3HV]60.010.5 [86]
Halomonas hydrothermalis MTCC5445Glycerol (5) (+Peptone)3.5Batch-P(3HB)-2.59[87]
Glycerol (3) (+Peptone)3.5Batch-P(3HB)-2.61
H. hydrothermalis SM-P-3MJatropha biodiesel byproducts (2)0.5Batch0.40P(3HB)75.80.30[88]
Bacillus sorensis
SM-P-1S		Jatropha biodiesel byproducts (2)0.5Batch0.283P(3HB)71.80/20[88]
Halomonas alkaliantarctica DSM 15686Biodiesel-derived glycerol (85%) (1)1.94Shake flask-P(3HB-3HV) [2.77 mol% 3HV]113.5 b[89]
Biodiesel-derived glycerol (85%) (5)1.94Shake flask-P(3HB-3HV) [1.82 mol% 3HV]185.8 b
Biodiesel-derived glycerol (85%) (8)1.94Shake flask-P(3HB-3HV)
[1.65 mol% 3HV]		93.0 b
Halomonas daqingensisAlgal biodiesel waste residue (Crude glycerol) (3)3.5Batch0.362P(3HB-3HV)65.20.236[90]
Salinivibrio sp. M318Glycerol + waste fish oil and sauce (as nitrogen source) (3)4.5Fed-batch5.7P(3HB), P(3HB-3HV), P(3HB-4HB) a [2.9 mol% 3HV]52.83[91]
Halomonas organivorans CCM 7142Waste frying oil (2)4Shake flask3.64P(3HB)61.982.26[91]
Halomonas hydrothermalis CCM 7104Waste frying oil (2)8Shake flask1.60P(3HB)23.760.38[91]
Waste frying oil (2)8Shake flask2.75P(3HB-3HV) a
[7.16 mol% 3HV]		47.171.29
Halomonas neptunia CCM 7107Waste frying oil (2)6Shake flask2.28P(3HB)55.711.27[91]
Waste frying oil (2)8Shake flask1.23P(3HB-3HV) a
[26.07 mol% 3HV]		15.850.19
Halomonas bluephagensis TD01Glucose (3) (60MMG medium with γ-butyrolactone + waste corn steep liquor; waste gluconate)6Continuous culture (Pilot:5 m3)100P(3HB-4HB) [13.5 mol% 4HB]600.6[92]
a: Precursor added; b: Ammonium citrate (0.1); c: (thrACB operon and ilvA gene coding for threonine dehydrogenase). -NR: Not reported
Based on a perusal of the key observation made on archaeal and bacterial capacities to metabolize different feedstocks and their PHA yielding capacities considering both PHA content (%) and PHA concentration (g/L), the following conclusions can be drawn (Table 3):
  • Archaeal feedstocks generally yield much higher PHA concentrations (up to 77.8 g/L) than bacterial feedstocks (max 10.5 g/L).
  • Bacterial systems achieve higher PHA content (95.26%) than archaea (max 87.5%).
  • Crude glycerol and sugar beet molasses appear to be the best bacterial feedstocks for industrial feasibility, while rice bran–corn starch mix and hydrolyzed whey dominate archaeal production.
  • Waste valorization is a key advantage in both cases, although archaea demonstrate broader substrate adaptability.
  • Archaea are better suited for large-scale biopolymer production, while bacteria are more cost-effective in non-sterile industrial settings.

6. Robust Contender for PHA Production

While traditional bacterial candidates such as Pseudomonas, Bacillus, and Ralstonia have been extensively studied for PHA production [94,95], recent research has shifted the focus toward extremophiles, particularly Halomonas spp. (Table 4). This genus can produce PHAs in bulk at a low cost, making it a promising candidate for NGIB.
  • Halomonas spp. as an optimal chassis for PHA production: Halomonas species, particularly H. bluephagenesis and H. campaniensis, have been identified as highly suitable hosts for PHA biosynthesis due to their fast growth, high tolerance, and ease of genetic manipulation [69,96]. These bacteria can thrive under unsterile conditions, with H. campaniensis reported to sustain growth in artificial seawater for over two months [32,97,98].
  • Genetic engineering strategies: Recent advancements in the genetic modification of Halomonas spp. involve the development of unique plasmids carrying inducible gene expression systems controlled by constitutive promoters [99,100,101]. Tools like CRISPR/Cas9 and CRISPRi have been employed to regulate metabolic flux, particularly the nicotinamide adenine dinucleotide hydride/nicotinamide adenine dinucleotide (NADH/NAD+) ratio, by deleting flavoprotein genes to enhance PHA synthesis in H. bluephagenesis [13,102,103,104,105]. Additionally, H. bluephagenesis has been engineered to optimize oxygen uptake under low oxygen conditions via inducible promoter control [106].
  • Enhancing PHA production through morphological and metabolic engineering: Genetic modifications, including the overexpression of sulA (encoding cell division inhibitor protein) or minCD and deletion of mreB, have resulted in higher cell densities [1,67,107,108]. In addition to the downstream processing techniques, these strategies promote the formation of larger cells containing larger PHA granules [66]. Moreover, self-flocculation mechanisms have been optimized to facilitate easy harvesting [109]. Synchronizing cell autolysis with substrate exhaustion has also been explored to improve the cost efficiency of PHA synthesis [110].
  • Industrial-scale achievements and economic feasibility: Studies have successfully produced PHA copolymers containing monomers, such as 3HB, 4HB, HHx, and functionally modified 3-hydroxyhex-5-enoate (HHxE) [92,111,112]. This has enabled industrial-scale PHA production, reaching biomass levels of 100 g/L and copolymer yields of 60 wt% in 5000 L reactors [92,113]. With these next-generation biotechnological advancements, the production cost of PHA is projected to decrease. The cost of P(3HB-co-4HB) production by genetically engineered H. bluephagenesis was reported to be USD 1.98 /kg by replacing γ-butyrolactone with unrelated carbon sources. The production cost was envisaged to be reduced further to 1.66–1.94 /kg for slaughtering waste streams. It was also observed that replacing glucose with gluconate can help to achieve a USD 0.75/kg cost-reduction [88].
The shift toward Halomonas spp. for PHA production represents a breakthrough in industrial biotechnology. These extremophiles have demonstrated remarkable potential for cost-effective large-scale PHA production through genetic modifications and optimized process parameters (Figure 2). Integrating advanced genetic tools and sustainable cultivation techniques is expected to drive the commercialization of PHAs as viable alternatives to petroleum-based plastics. Enhancing PHA recovery from extremophiles, particularly halophiles, requires modifications to conventional extraction methods. Due to their high intracellular osmotic pressure, extreme halophiles lyse easily in hypotonic conditions, eliminating the need for harsh chemical, enzymatic, or mechanical disruption. Optimization involves controlled osmotic shock using deionized water and centrifugation to recover intact PHA granules. Reducing salt contamination and improving granule purity may require additional washing steps. Moreover, scalable strategies should focus on minimizing dilution effects and optimizing biomass harvesting from high-salinity cultures. Integrating eco-friendly extraction processes can enhance yield, reduce costs, and improve the sustainability of PHA production [6,40,114].
Table 4. Halomonas as a promising microbe for sustainable polyhydroxyalkanoate production.
Table 4. Halomonas as a promising microbe for sustainable polyhydroxyalkanoate production.
Distinctive TraitsReferences
Extremophilic bacteria with high salt tolerance and higher oxygen uptake, even at extremely low oxygen levels, are suitable for industrial PHA production[32,69,92,96,98,106]
Microbes engineered with a constitutive promoter-mediated genetic system[99,100,101,102]
Modified cell shape (filamentous) with higher density, larger PHA granules for easy recovery—downstream processing achieved by deleting gene (mreB) in association with overexpression of genes of cell division (minCD or sulA)[66,67,107,108,109]
CRISPR/Cas9 and CRISPRi-based multi-purpose PHA synthase and manipulating carbon flux and energy regulation (NADH/NAD+), enhanced acetyl-CoA diversion leading to enhanced PHA yield[13,103,104,105]
Diversity of PHA copolymers with monomers of 3-hydroxybutyrate, 4-hydroxybutyrate, and 3-hydroxy hexanoate[89,111,112]
Commercial level PHA production: 5000 L reactors[92,113]
PHA: polyhydroxyalkanoate; CRISPR/Cas9: Clustered regularly interspaced short palindromic repeats Cas protein systems; CRISPRi: Clustered regularly interspaced short palindromic repeats interference; NADH/NAD+: Nicotinamide adenine dinucleotide hydride/Nicotinamide adenine dinucleotide; mreB (encoding dynamic cytoskeletal protein); minC and minD (encoding Z-ring positioning protein); sulA (encoding cell division inhibitor protein).

7. Perspectives

Advancing NGIB for PHA production requires research across multiple areas. Metabolic engineering and synthetic biology focus on enhancing metabolic pathways to improve PHA yield and monomer composition, utilizing CRISPR/Cas-based genome editing to fine-tune regulatory networks, and engineering robust microbial chassis for efficient biosynthesis. Extremophile-based fermentation leverages halophilic and thermophilic bacteria for cost-effective, unsterile production while developing adaptive evolution strategies to enhance microbial tolerance. Feedstock optimization and waste valorization explore lignocellulosic biomass, agricultural waste, and industrial by-products alongside microbial consortia for efficient bioconversion of complex substrates. Process automation and AI-driven optimization integrate machine learning and AI to refine fermentation parameters and develop real-time monitoring systems for enhanced process control. For simplified recovery, cost-effective downstream processing focuses on solvent-free extraction techniques to minimize environmental impact and investigate self-flocculating and autolytic bacterial strains. Sustainability and commercialization efforts assess life cycle impacts to enhance environmental benefits while establishing scalable bioprocesses to reduce costs and compete with petroleum-based plastics.
PHA production from halophiles presents several challenges, including high salinity requirements, which complicate large-scale fermentation and downstream processing. Maintaining optimal growth conditions requires specialized bioreactors resistant to corrosion and salt accumulation. Also, halophilic cultures often exhibit slower growth rates and lower biomass yields than mesophilic counterparts. The presence of intracellular salts in harvested biomass can hinder PHA purification, necessitating additional washing steps. Moreover, the economic viability of halophilic PHA production remains a concern due to the costs associated with maintaining extreme conditions.
Future directions include metabolic engineering to enhance PHA accumulation and cell growth under moderate salinity, reducing process complexity. Optimizing nutrient formulations and developing cost-effective halophilic feedstocks can improve productivity. Additionally, advances in continuous bioprocessing and integrated recovery methods, such as membrane filtration, can enhance efficiency. Exploring novel halophilic strains with superior PHA yield and stress tolerance will further improve sustainability and commercial feasibility.

8. Conclusions

PHAs hold immense promise as biodegradable alternatives to conventional plastics; however, their large-scale production remains limited by high costs and technical challenges. Traditional PHA production relies on pure microbial cultures and refined carbon sources, which makes it economically unfeasible. The emergence of NGIB represents a paradigm shift by leveraging extremophilic microbes, such as halophiles and thermophiles, as a robust chassis for cost-effective and sustainable bioprocesses. These microorganisms naturally thrive in extreme environments that suppress microbial contamination, reducing the need for costly sterilization and stringent process control. Advancements in metabolic engineering, synthetic biology, and feedstock diversification have enhanced the efficiency of PHA production. Utilizing alternative carbon sources, such as biowaste, syngas, methane, and CO2, reduces the dependence on expensive refined sugars. Replacing freshwater with seawater or treated wastewater significantly lowers operational costs and environmental impacts. PHA production can be economically viable by integrating continuous culture systems with energy-efficient bioreactors. Future research should optimize metabolic pathways and fermentation strategies to ensure scalable industrial implementation, ultimately positioning PHA as a competitive and sustainable alternative to petroleum-based plastics.

Author Contributions

Conceptualization, V.C.K.; methodology, V.C.K., C.G. and R.V.S.; validation, V.C.K., R.V.S. and C.G.; formal analysis, V.C.K. and R.V.S.; resources, J.-K.L.; data curation, V.C.K.; writing—original draft, V.C.K. and J.-K.L.; writing—review and editing, V.C.K. and R.V.S.; supervision, V.C.K. and J.-K.L.; funding acquisition, J.-K.L. All authors have read and agreed to the published version of the manuscript.

Funding

This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) and funded by the Ministry of Science, ICT, and Future Planning (2022M3A9I5015091, 2022M3A9I3082366, RS-2024-00351665, RS-2024-00440681).

Institutional Review Board Statement

Not applicable.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

The following abbreviations are used in this manuscript:
PHAPolyhydroxyalkanoates
NGIBNext-Generation Industrial Biotechnology
scl-PHAShort-chain-length polyhydroxyalkanoate
mcl-PHAMedium-chain-length polyhydroxyalkanoate
P(3HB)Poly(3-hydroxybutyrate)
P(3HB-3HV)Poly(3-hydroxybutyrate-3-hydroxyvalerate)
CDWCell dry weight
M.Wt.Molecular weight
SCBSugarcane bagasse
NADH/NAD+Nicotinamide adenine dinucleotide hydride/Nicotinamide adenine dinucleotide
CRISPR/Cas9Clustered regularly interspaced short palindromic repeats Cas protein systems
CRISPRiClustered regularly interspaced short palindromic repeats interference

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Polymers 17 00853 g001
Figure 1. Unique features of current- vs. next-generation industrial biotechnology.
Figure 1. Unique features of current- vs. next-generation industrial biotechnology.
Polymers 17 00853 g001
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Figure 2. The significance of extremophiles for producing polyhydroxyalkanoates.
Figure 2. The significance of extremophiles for producing polyhydroxyalkanoates.
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Table 1. Diversity of halophilic archaeal microbes to produce polyhydroxyalkanoates.
Table 1. Diversity of halophilic archaeal microbes to produce polyhydroxyalkanoates.
PHA ProducerSubstrate
(%)		Salt (NaCl)
(%)		ReactorCell Dry Mass
(g/L)		Polyhydroxyalkanoate (PHA)References
Composition (%mol Copolymer)Content (wt%)Yield
(g/L)
Pure Sugars
Haloarcula marismortui ATCC 43049 (33960/pWLEC)Glucose (2)20Shake flask15.4P(3HB) 182.77[47]
Haloferax mediterraneiGlucose a (1)20Fed-batch85.8P(3HB-3HV)
[10.7 mol% 3HV]		48.641.69[48]
Halogranum amylolyticum TNN58Glucose a (1)20Fed-batch (7.5 L)5.4P(3HB-3HV)
[20.1 mol% 3HV]		26.61.4[50]
Halogeometricum borinquense E3Glucose a (2)20Shake flask2.1P(3HB-3HV)
[21.47 mol% 3HV]		73.511.54[51]
Natrinema ajinwuensis RM-G10Glucose a (1)20Shake flask (Repeat batch)24.2P(3HB-3HV)
[13.93 mol% 3HV]		6114.78[52]
Biowastes
Starch-based feedstocks
H. mediterraneiExtruded starch (1)23.4Shake flask39.4P(3HB-3HV) [10.4 mol% 3HV]50.820/01[53]
Extruded rice bran: corn starch::1:8) (1)23.4Fed-batch140P(3HB-3HV) [10.4 mol% 3HV]55.677.84[54]
Extruded corn starch (1)23.4Fed-batch62.6P(3HB-3HV) [10.4 mol% 3HV]38.724.2
H. mediterranei
CGMCC 1.2087		Starch (1) + AS-168 medium20Shake flask7.33P(3HB-3HV)
[9.33 mol% 3HV]		18.211.33[49]
Starch (1) + MST medium20Shake flask7.01P(3HB-3HV)
[13.37 mol% 3HV]		24.881.74
Natrinema sp. 1KYS1Starch (2)25Shake flask2.21P(3HB-3HV)2.480.055[46]
Corn starch (2)25Shake flask0.17P(3HB-3HV)
[25 mol% 3HV]		53.140.075
Dairy and ethanol industry waste
H. mediterranei DSM 1411 Hydrolyzed whey15.6Shake flask24P(3HB-3HV)
[8 mol% 3HV]		5012[55]
Hydrolyzed whey sodium valerate and γ-butyrolactone15Batch16.8P(3HB-3HV-4HB)
[21.8 mol% 3HV; 5.1 mol% 4HB]		87.514.7[56]
Pre-treated vinasse (25%)20Shake flask28.14P(3HB-3HV)
[12.36 mol% 3HV]		7019.7[57]
Pre-treated vinasse (50%)20Shake flask26.34P(3HB-3HV)
[14.09 mol% 3HV]		6617.4
Rice-based ethanol stillage20Shake flask23.12P(3HB-3HV)
[15.4 mol% 3HV]		7116.42[58]
H. marismortui MTCC 1596Raw vinasse (10)20Shake flask12P(3HB) 232.8[59]
Raw vinasse (pre-treated—activated carbon) (100)20Shake flask15P(3HB) 304.5
Natrinema sp. 1KYS1Whey (2)25Shake flask0.454P(3HB-3HV)19.920.091[46]
Agro-industrial waste and other feedstocks
Natrinema sp. 1KYS1Melon waste (2)25Shake flask0.37P(3HB-3HV)10.50.039[46]
Apple waste (2)25Shake flask2.55P(3HB-3HV)3.020.077
Tomato waste (2)25Shake flask3.85P(3HB-3HV)12.030.46
H. mediterraneiOlive mill wastewater (15)22Shake flask10P(3HB-3HV)
[6.5 mol% 3HV]		434.3[60]
Halogeometricum borinquense E3Sugarcane bagasse hydrolysate (20)20Shake flask3.17P(3HB-3HV)
[13.29 mol% 3HV]		50.41.59[61]
Starch (2)20Shake flask6.2P(3HB-3HV)
[13.11 mol% 3HV]		74.194.6[62]
Cassava waste hydrolysate (10)20Shake flask3.4P(3HB-3HV)
[19.65 mol% 3HV]		44.71.52
a: Precursor added. P(3HB): poly(3-hydroxybutyrate); P(3HB-3HV): poly(3-hydroxybutyrate-3-hydroxyvalerate).
Table 3. A comparison of the archaeal and bacterial polyhdroxyalkanoate-producing potential from biowastes.
Table 3. A comparison of the archaeal and bacterial polyhdroxyalkanoate-producing potential from biowastes.
CriteriaArchaea Bacteria
Max. PHA Yield (g/L)77.8 (Rice bran-corn starch mix)10.5 (Optimized crude glycerol)
Max. PHA Content (%)87.595.26
Best FeedstocksHydrolyzed whey, rice bran-corn starch, ethanol wasteFructose syrup, sugar beet molasses, crude glycerol
Copolymer Composition21.8 mol% 3HV, 5.1 mol% 4HB52 mol% 3HV, high M.Wt. PHA
Waste ValorizationStrong (vinasse, bagasse, agro-waste)Moderate (biodiesel byproducts, wheat straw)
Industrial FeasibilityMore established (high yield and adaptability to hypersaline environments)More cost-effective (low-cost substrates, non-sterile fermentation)
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Kalia, V.C.; Singh, R.V.; Gong, C.; Lee, J.-K. Toward Sustainable Polyhydroxyalkanoates: A Next-Gen Biotechnology Approach. Polymers 2025, 17, 853. https://doi.org/10.3390/polym17070853

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Kalia VC, Singh RV, Gong C, Lee J-K. Toward Sustainable Polyhydroxyalkanoates: A Next-Gen Biotechnology Approach. Polymers. 2025; 17(7):853. https://doi.org/10.3390/polym17070853

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Kalia, Vipin Chandra, Rahul Vikram Singh, Chunjie Gong, and Jung-Kul Lee. 2025. "Toward Sustainable Polyhydroxyalkanoates: A Next-Gen Biotechnology Approach" Polymers 17, no. 7: 853. https://doi.org/10.3390/polym17070853

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Kalia, V. C., Singh, R. V., Gong, C., & Lee, J.-K. (2025). Toward Sustainable Polyhydroxyalkanoates: A Next-Gen Biotechnology Approach. Polymers, 17(7), 853. https://doi.org/10.3390/polym17070853

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