Search Results (152)

The prevention of biofilm formation and algal biodeterioration on building materials, particularly on cultural heritage sites, is a growing concern. Due to regulatory restrictions on conventional algicidal biocides in Europe, natural alternatives such as essential oils are gaining interest for their potential use in heritage conservation. This study evaluates the anti-algal activity of Salvia officinalis and Equisetum arvense (essential oils, hydrolates, and extracts) against a mixed culture of five green algae species (Bracteacoccus minor, Stichococcus bacillaris, Klebsormidium nitens, Chloroidium saccharophilum, and Diplosphaera chodatii). The plant materials were processed using hydrodistillation and solvent extraction, followed by chemical characterization through gas chromatography–mass spectrometry (GC-MS). Biological efficacy was assessed by measuring algal growth inhibition, changes in biomass colour, chlorophyll a concentration, and fluorescence. S. officinalis yielded higher extract quantities (extraction yield: 23%) than E. arvense and contained bioactive compounds such as thujone, camphor, and cineole, which correlated with its strong anti-algal effects. The essential oil of S. officinalis demonstrated the highest efficacy, significantly inhibiting biofilm formation (zones of inhibition: 15–94 mm) and photosynthetic activity at 0.5% concentration (reduction in chlorophyll a concentration 90–100%), without causing visible discolouration of treated surfaces (∆E < 2). These findings highlight the potential of S. officinalis essential oil as a natural, effective, and material-safe algicidal biocide for the sustainable protection of cultural heritage sites. Full article

Hydraulic shear has been widely accepted as one of the essential factors modulating phytoplankton growth. Previous experimental studies of algal growth have been conducted at the macroscopic level, and direct observation at the cell scale has been lacking. In this study, an algal-cell dynamic continuous observation platform (ACDCOP) is proposed with a parallel-plate flow chamber (PPFC) to capture cellular growth images which are then used as input to a computer vision algorithm featuring a pre-trained backpropagation neural network to quantitatively evaluate the volumes and volumetric growth rates of individual cells. The platform was applied to investigate the growth of Scenedesmus quadricauda cells under different hydraulic shear stress conditions. The results indicated that the threshold shear stress for the development of Scenedesmus quadricauda cells was 270 µL min⁻¹ (5.62 × 10⁻⁵ m² s⁻³). Cellular growth was inhibited at very low and very high intensities of hydraulic shear. Among all the experimental groups, the longest growth period for a cell, from attachment to PPFC to cell division, was 5.7 days. Cells with larger initial volumes produced larger volumes at division. The proposed platform could provide a novel approach for algal research by enabling direct observation of algal growth at the cell scale, and could potentially be applied to investigate the impacts of various environmental stressors such as nutrient, temperature, and light on cellular growth in different algal species. Full article

Numerous remediation strategies exist for cyanobacterial harmful algal blooms (cyanoHABs); however, most are limited by challenges of scalability and adverse off-target effects on the surrounding ecosystem. Germicidal ultraviolet light (UV-C) has emerged as a promising method for suppressing cyanoHABs in a sustainable, chemical-free manner that is both scalable and results in limited off-target ecological effects in the surrounding area. In this study, the US Army Engineer Research and Development Center’s (ERDC)’s CyanoSTUN^TM (Cyanobacterial Suppression Through Ultraviolet-Light-C Neutralization) vessel was deployed to a cyanoHAB as part of a field trial to determine whether UV-C could effectively suppress cellular growth, degrade associated cyanotoxins, and inhibit harmful phytoplankton species more readily than beneficial species without the addition of chemicals. The cyanoHAB exhibited an average cyanobacteria abundance of 3.75 × 10⁵ cells/mL (n = 5, SD = 6.76 × 10⁴ cells/mL) and average total microcystin concentration of 3.5 µg/L (n = 5; SD = 0.24 µg/L). Pre- and post-treatment samples were collected and re-grown for 9 days in the laboratory to observe differences in microcystin, chlorophyll a, and phycocyanin concentrations, optical density, cell density, and community composition. The results of the field trial showed that the CyanoSTUN UV-C treatment effectively suppressed the growth of the cyanobacteria community for approximately two days at the three tested UV-C doses. The CyanoSTUN UV-C treatment also demonstrated a sustained, dose-dependent effect on microcystin concentration; the average reduction in microcystin concentration for 15, 30, and 45 mJ/cm² treatment doses was 31.6% (n = 10, SD = 20.1%; 1.3 µg/L reduced), 45.7% (n = 10, SD = 10.8%; 1.9 µg/L reduced), and 49.9% (n = 10, SD = 8.2%; 1.7 µg/L reduced), respectively, over the 9-day regrowth period. Non-cyanobacteria were too scarce in this CyanoHAB to conclude whether the CyanoSTUN UV-C inhibits harmful phytoplankton species more readily than beneficial species. Further field studies with the CyanoSTUN^TM are required to validate performance under more severe cyanoHAB conditions, however the results reported herein from the first field trial with the CyanoSTUN^TM suggest that this treatment method may offer water managers confronted with a CyanoHAB the ability to rapidly and safely pause a bloom for multiple days and reduce the risks posed by its associated cyanotoxins without adding chemicals. Full article

Allelochemicals are recognized as promising algaecides due to their environmental safety. Para-tert-butylcatechol (TBC) and L-lysine exhibit significant potential in suppressing harmful algal blooms (HABs); however, their combined effects and algae inhibition mechanisms remain unelucidated. Therefore, this study systematically investigated the growth inhibition of Microcystis aeruginosa by TBC and L-lysine individually and in combination, while simultaneously examining their combined effects on algal growth, cell membrane integrity, photosynthetic activity, antioxidant responses, and microcystin production. The results revealed a significant interactive effect between TBC (0.04 mg/L) and L-lysine (1 mg/L), achieving over 90% growth inhibition within 96 h. The combined treatment significantly inhibited M. aeruginosa growth through impaired photosynthetic efficiency and elevated oxidative stress. Compared to the control group, the treatment group exhibited a continuous decline in chlorophyll-a content, phycobiliprotein levels, F_v/F_m, YII, α, and rETR_max, while phosphoenolpyruvate carboxylase (PEPC) activity decreased by 96.48% by day 8. And antioxidant enzymes, including superoxide dismutase (SOD) and reduced glutathione (GSH), showed a progressive increase in activity. In addition, the structure and integrity of the cell membrane of M. aeruginosa were damaged after treatment, and the conductivity of the treatment groups increased continuously from 2.32 to 4.63 μs/cm. In addition, under combined treatment, intra- and extracellular microcystin levels initially increased (peaking at day 2) but sharply declined thereafter, becoming significantly lower than controls by day 8. These findings highlight the potential of combining TBC and L-lysine as an eco-friendly and cost-effective strategy for mitigating M. aeruginosa-dominated harmful algal blooms. Full article

Harmful Raphidiopsis raciborskii blooms threaten aquatic ecosystems via toxin production, hypoxia induction, and biodiversity loss. To elucidate the synergistic regulatory mechanisms of Fe³⁺ and phosphorus (P) in cyanobacterial growth, we used a sterile pure culture system under laboratory conditions. We set different phosphorus sources (organic phosphorus and inorganic phosphorus) and low phosphorus concentration of R. raciborskii culture medium for culture, and set different Fe³⁺ addition amount to determine the basic growth index of cyanobacteria cells and the phosphorus content of different components. The results revealed that under conditions of sufficient inorganic phosphorus, there was a logarithmic relationship between ferric ammonium citrate (Fe³⁺) and the specific growth rate of R. raciborskii. Fe³⁺ > 2 mg/L enhanced IPS enrichment and biomass accumulation. However, in oligotrophic or mesotrophic environments with low inorganic phosphorus concentrations, the effect of Fe³⁺ on the growth of R. raciborskii contrasted with that observed in high-IP (eutrophic) environments, exhibiting a pattern of ‘low promotion and high inhibition’. Under organic phosphorus conditions, R. raciborskii converted phosphorus by increasing alkaline phosphatase activity (APA), but this metabolic compensation failed to restore physiological functions, resulting in growth suppression and enhanced cellular phosphorus reserves. Our results establish quantitative linkages between Fe³⁺-P co-limitation thresholds and algal adaptive responses, providing mechanistic insights for controlling bloom dynamics through targeted manipulation of Fe-P bioavailability. Full article

Global kelp farming is garnering growing attention for its contributions to fishery yields, environmental remediation, and carbon neutrality efforts. Kelp farming systems face escalating pressures from compounded climatic and environmental stressors. A severe outbreak disaster caused extensive kelp mortality and significant economic losses in Rongcheng, China, one of the world’s largest kelp farming areas. This study investigated the growth and physiological responses of Saccharina japonica to combined stressors involving three levels of N:P ratios (10:1 as a control; 100:1 and 500:1 to represent phosphorus deficiency stress) and two temperature/light regimes (12 °C, 90 μmol photons m⁻² s⁻¹ as a control, and 17 °C, 340 μmol photons m⁻² s⁻¹ to represent thermal and high-light stress). The results demonstrated that phosphorus deficiency significantly inhibited the relative growth rate of kelp (24% decrease), and the strongest growth inhibition in kelp was observed at the N:P ratio of 500:1 combined with thermal and high-light stress. The algal tissue was whitened due to its progressive disintegration under escalating stress, coupled with damage to its chloroplasts and nucleus ultrastructures. Phosphorus-deficiency-induced declines in photochemistry (27–56% decrease) and chlorophyll content (63% decrease) were paradoxically and transiently reversed by thermal and high-light stress, but this “false recovery” accelerated subsequent metabolic collapse (a 60–75% decrease in the growth rate and a loss of thallus integrity). Alkaline phosphatase was preferentially activated to cope with phosphorus deficiency combined with photothermal stress, while acid phosphatase was subsequently induced to provide auxiliary support. S. japonica suppressed its metabolism but upregulated its nucleotides under phosphorus deficiency; however, the energy/amino acid/coenzyme pathways were activated and a broad spectrum of metabolites were upregulated under combined stressors, indicating that S. japonica employs a dual adaptive strategy where phosphorus scarcity triggers metabolic conservation. Thermal/light stress can override phosphorus limitations by activating specific compensatory pathways. The findings of this study provide a foundation for the sustainable development of kelp farming under climate and environmental changes. Full article

The increasing pollution of polystyrene (PS) and polymethyl methacrylate (PMMA) microplastics (MPs) has become a global marine environmental problem. Diatoms contribute nearly 40% of marine primary productivity and shape the nitrogen cycle in the oceans. However, the persistence of the phytotoxicity of MPs on diatoms, especially nitrogen assimilation, remains largely unknown. To examine the persistence of PS and PMMA toxicity in diatoms, two subexperiments (a 96 h exposure followed by a recovery phase) were conducted on Thalassiosira pseudonana at concentrations ranging from 0.001 to 1 mg/L. The results showed that PS and PMMA inhibited algal growth by 3.76–6.49% and 4.44–8.37%; increased oxidative stress by 10.06–30.51% and 30.46–38.12%; and caused ultrastructural damage by 14.24–25.56% and 12.28–20%, respectively, consistent with the downregulation of glyoxylate, dicarboxylate metabolism, and glutathione metabolism. At the recovery stage, the algal density induced by PS was significantly recoverable at 0.001 and 0.01 mg/L, consistent with the enhanced carbohydrate metabolisms. After recovery, the cell permeability and reactive oxygen species (ROS) levels induced by PS and PMMA were significantly decreased at 1 mg/L, respectively, which was closely related to the downregulation of glycine, serine, and threonine metabolism and the upregulation of pantothenate and coenzyme A biosynthesis. Moreover, the inhibition of nitrogen assimilation enzymic activities induced by PS and PMMA was significantly recovered at 1 mg/L despite the downregulation of nitrogen metabolism. This study highlights the phenomena and mechanisms of phytotoxicity and recovery, and provides new insights for comprehensive understanding and evaluation of environmental risks of MPs. Full article

The experiments in this study investigated the toxicity of naphthenic acids (NAs) on the algal culture Spirulina platensis. The tests monitored the progression of the algal suspension in media contaminated with various concentrations of naphthenic acids. The evolution of the algal culture during the metabolism of NAs was investigated. The monitoring also included the determination of the values of some parameters during the biodegradation process (pH, conductivity, cell viability, dissolved oxygen). Optical density measurements (OD₆₀₀) were used to quantify the growth of Spirulina platensis, alongside the determination of the sedimentation index (IS). Cell viability was assessed microscopically using TEM and optical microscopy. The results facilitated the estimation of the percentage of cell growth inhibition and the inhibitory concentration value, determined by estimating ECb50 (concentration of NAs corresponding to 50% inhibition). The chemical quantification of naphthenic acids in the samples analyzed was performed by calculating the acidity value (AV) and characterizing the naphthenic acids through FTIR analysis. The graphical representation of ECb50 was established by extrapolating to a concentration of 110 mg/mL of naphthenic acids. We have demonstrated that pollution caused by NAs can be mitigated by the algae Spirulina platensis, which can metabolize these compounds and thus biodegrade them. Full article

Besides biomass production, some microalgae have been used to treat wastewater contamination. However, in general, high concentrations of heavy metals significantly inhibit algal growth. We thus need to find ways to promote the resistance of microalgae to heavy metals, increase their growth rate under stress, and achieve coupling of heavy metal removal and biomass production simultaneously. In this review, mechanisms for removal of heavy metals by microalgae are proposed. Effects of exogenous chemical additives (dissolved organic matters, formaldehyde, sulphate, phosphate, nitric oxide donors, etc.) on algal biosorption to heavy metals are summarized. Genetic manipulation and microalgal strain selection strategies are also introduced, especially for the acid-tolerant strains with high biosorption efficiencies to Cr(VI) and Cd²⁺ at low pH conditions. Recent advances in (semi)continuous heavy-metal-bioremediation and biomass-production coupled system with immobilized microalgae, as well as challenges and solutions to the commercialization and industrialization of the coupled system were discussed. Full article

The n-3 long-chain polyunsaturated fatty acids (n-3 LC-PUFAs) have a key role in maintaining fish growth and health. However, fish oil (FO), the main source of n-3 LC-PUFAs, is in relative shortage due to the rapid development of the aquaculture industry. In this study, we investigated the efficacy of replacing fish oil with mixtures of algal oil (AO) from Schizochytrium sp. and terrestrially sourced oils (animal oil poultry oil (PO) or vegetable oil rapeseed oil (RO)) in the diets of juvenile tiger puffer (average initial body weight 23.8 ± 1.51 g). An 8-week feeding trial was conducted using three experimental diets: a control diet containing 6% added FO (control FO-C) and two diets with 3% AO + 3% PO or RO (groups AO+PO and AO+RO, respectively), replacing FO. Each diet was fed to triplicate tanks with 25 fish in each tank. The weight gain, feed conversion ratio, body composition, and serum biochemical parameters were not significantly different among the three groups, except that the AO+PO group had a significantly lower muscle lipid content than the other two groups. The AO-added diets significantly increased the DHA content in whole fish, muscle, and liver samples but significantly reduced the EPA content. The oil mixture treatments significantly increased the contents of monounsaturated fatty acid (MUFA) but significantly decreased the contents of saturated fatty acids (SFAs) in the liver and whole fish samples. However, the MUFA and SFA contents in the muscle samples were not significantly different among the dietary groups. The diets with oil mixtures did not affect the hepatic histology but tended to result in the atrophy of intestinal villi. The treatment diets downregulated the hepatic gene expression of proinflammatory cytokines (il-1β and tnf-α) and the fibrosis marker gene, acta2. However, the AO+PO diet inhibited the intestinal gene expression of the tight junction protein, claudin 18. In the muscle, the treatment diets upregulated the expression of genes related to cell differentiation and apoptosis (myod, myog, myf6, myf5, bcl-2, and bax). In conclusion, Schizochytrium sp. oil in combination with terrestrial oils (poultry oil or rapeseed oil) can be an effective alternative to fish oil in the diets of tiger puffer, but the mixing strategy may be better modified in consideration of intestinal health. Full article

Preventing fouling is crucial for maintaining ship performance, as it reduces speed, increases fuel consumption, raises greenhouse gas emissions, and spreads invasive species. Irgarol 1051, an antifouling agent (2, methythiol-4, tert-butylamino, 6-cyclopropylamino, s-triazine), is a toxic compound that impacts various marine species. It inhibits algal growth and disrupts key metabolites, posing a threat to the marine ecosystem. This study aimed to assess the toxic effects of Irgarol 1051 on Chlorella salina and Dunaliella bardawil, two nutrient-rich marine algae commonly used in fish feed. In addition, the suitability of the Mediterranean Sea coast for algal proliferation was assessed using geospatial techniques. The data were statistically examined using a two-way ANOVA test. Lethal and sublethal effects of Irgarol 1051 were measured in the laboratory to identify the consequences of this biocide on certain metabolite compositions. EC50 for C. salina and D. bardawil was estimated to be 0.50 µg·L⁻¹ and 0.025 µg·L⁻¹ respectively. IR spectroscopy of total cell constituents, protein profile, and the damaging effects of antioxidants have been evaluated for the two algal species. The findings of this study revealed that Irgarol 1051 negatively affected all the examined metabolites in both algal species, with more pronounced impacts on the wall-less alga Dunaliella bardawil compared to the walled alga Chlorella salina. A notable increase in total antioxidants was observed in both algae as the Irgarol concentration increased. The study reveals high algal growth areas near the Nile Delta along the Egyptian coast, potentially vulnerable to the effects of Irgarol 1051 due to nutrient runoff and eutrophication. The spatial analyses showed that the growth of C. saline and D. bardawil in Egyptian seawater is high in front of the Nile delta governorates: Port Said, Damietta, and Dakhalia shores reporting 6, 4.5, and 4 mg·m⁻³, respectively. The level of mass chlorophyll “a” in front of the Egyptian northern governorates can be ordered as follows: Port Said > Damietta > Dakahlia > North Sinia > Kafr El-Sheikh > Alexandria > Matrouh. This study highlights the use of spatial analyses to assess algal distribution, pollution impact, and ecosystem vulnerability along the Egyptian Mediterranean coast for effective environmental management. Full article

Silver nanoparticles (AgNPs), synthesised using Chlorella vulgaris algal extract and silver nitrate, are studied in medicine for their antibacterial properties in poultry. This study assessed the effect of AgNPs on bacterial inhibition and early development and blood parameters in Ross 308 chicken embryos. AgNPs were characterised using transmission electron microscopy, scanning electron microscopy with a focused ion beam, UV–Vis spectroscopy, and a zetasizer. The antibacterial properties of the AgNP colloid against S. enterica were assessed using minimal inhibitory concentration, minimal bacterial concentration, and PrestoBlue assays. AgNP colloid (2 mg/L) was injected into egg albumen on day 0. Chicken embryos were incubated for 3 and 16 d. The effect of AgNPs on 3 d old embryos was evaluated based on mortality and somite count using the Hamburger–Hamilton classification. For older embryos, mortality, dimensions, anatomical changes, organ mass, plasma liver enzymes and antioxidants, and red blood cell morphology were determined. Blood samples from the control group embryos were assessed for the impact of AgNPs on hemolysis. AgNPs inhibited S. enterica growth at concentrations >6.75 mg/L. A 3 d exposure to AgNPs caused an insignificant decrease in the number of somites without affecting embryo mortality. However, a 16 d exposure to AgNPs reduced live embryos and plasma antioxidants, changed the levels of ALT, AST, and GGT, altered red blood cell morphology, and caused hemolysis. Toxicity of AgNPs was model-dependent, whereby the chicken embryo was more sensitive to AgNPs than the bacterium. Full article

Nanoplastics (NPs), an emerging pollutant distributed in different sizes in the aquatic environment, adversely affect aquatic ecosystems. However, knowledge of the effects of NPs of various sizes on phytoplankton, especially freshwater microalgae, is still limited. In this study, we explore the effects of three polystyrene NPs (PS-NPs) with different particle sizes (20, 50, and 80 nm) on the chronic toxicity of a widely distributed freshwater microalga, Chlorella pyrenoidosa. The results showed that PS-NPs-20, PS-NPs-50, and PS-NPs-80 promoted the growth of C. pyrenoidosa at the early stage of exposure, with the highest promotion rates of 46.1%, 56%, and 86.2%, respectively. PS-NPs-20 and PS-NPs-50 inhibited the photosynthesis and growth of C. pyrenoidosa during the mid- and late-exposure periods and also induced an increase in the secretion of reactive oxygen species and extracellular polymers. The highest inhibition rates were 33.2% and 13.6%, respectively. By contrast, the growth-promoting effect of PS-NPs-80 continued until the middle stage, and it was only at the late stage of exposure that some growth-inhibitory effects occurred, with the highest inhibition rate of only 7.8%. The results of transmission electron microscopy showed that PS-NPs-20 damaged algal cells more severely than PS-NPs-50 and PS-NPs-80 on day 21. Notably, a size-dependent effect of PS-NPs was observed on the toxicity of C. pyrenoidosa, but no dose-dependent effect was found. These results will improve our understanding of the toxicity of PS-NPs to microalgae and may provide a basis for evaluating the ecological risk of PS-NPs in freshwater environments. Full article

Carbon source limitation is a critical factor restricting the treatment efficiency of domestic wastewater by algae–bacteria consortia. Using agricultural waste as an external carbon source to enhance purification performance holds significant potential. This study investigated the effects of peanut shell powder (PSP) on wastewater treatment in algae–bacteria consortia. The results demonstrated that the optimal PSP dosage (2 mg/L) improved the removal efficiencies of TN, TP, and COD by 29.6%, 40.9%, and 18.7%, respectively. In contrast, excessive PSP reduced the removal performance. The primary mechanism by which PSP influenced the algae–bacteria consortia involved changes in microbial biomass and community structure. An optimal PSP dosage promoted the proliferation of the dominant algal species, Chlorella, enhanced photosynthetic activity, and increased the relative abundance of Rhodanobacter, known for its effective degradation of benzene compounds. Conversely, excessive PSP caused microbial cell rupture, inhibited Chlorella growth and photosynthesis, and elevated the abundance of Microcystis and Brevundimonas, which pose significant health risks. In conclusion, PSP can improve effluent quality and safety in algae–bacteria consortia, which represents a green, economical pathway for optimizing wastewater treatment processes. Full article

Eutrophication and its resultant cyanobacterial blooms are a severe environmental issue in global water bodies, and phosphate is regarded as one of the primary triggers. In this study, the in situ-synthesized heated kaolinite lanthanum hydroxide composite (HKL-LH) was used to treat cyanobacterial blooms through phosphate removal. A typical cyanobacteria species—Microcystis aeruginosa—was selected as the target organism. HKL-LH efficiently removed phosphate in the solution with the inoculation of M. aeruginosa over the course of one day. A good performance of HKL-LH on control cyanobacterial blooms with initial cell densities ranging from 10⁴ cells mL⁻¹ to 10⁵ cells mL⁻¹ was observed. Although the genetic expression relating to photosynthesis and cell division was upregulated under the stress of phosphorus deficiency, M. aeruginosa growth was significantly inhibited, i.e., the inhibition rate of up to 98% was achieved by 0.1g L⁻¹ of HKL-LH. In addition to cell growth, the photosynthetic activity and viability of M. aeruginosa cells were decreased by HKL-LH. Furthermore, the production of associated toxins (microcystins) and algal organic matters were effectively inhibited, which can reduce the ecological risk and challenges that follow water treatment. In this study, it is shown that HKL-LH has excellent application potential in the mitigation of cyanobacterial blooms in eutrophic water. Full article