Oxidative stress is a mediator for increased lipid accumulation in a newly isolated Dunaliella salina strain

Bioremediation of perfluorooctanoic acid using microalgae with a transcriptomic approach

Microalgal-mediated bioremediation technologies offer sustainable strategies for removal of emerging contaminants in aquatic environments. However, the molecular mechanisms and bioremediation pathways in microalgal species involved in the degradation of persistent organic pollutant perfluorooctanoic acid (PFOA) remain largely unexplored and poorly characterized. This study explored the potential of four microalgal strains for PFOA treatment and examined the expression of key functional genes through transcriptomic analysis. Scenedesmus quadricauda emerged as the most promising candidate for PFOA removal, exhibiting a high removal efficiency of 58.2 % (1.22 mg-PFOA/g-microalgae) at an initial PFOA concentration of 5 ppm. The mass balance analysis of PFOA removal by S. quadricauda revealed that 44.8 % of the PFOA was removed through bioaccumulation, and 12.8 % through biosorption. The chromatographic analysis confirmed that a portion of the bioaccumulated PFOA (0.58 %, 22.7 μg/L) was biodegraded by the biological removal mechanism in microalgae and identified by-products of PFOA. When S. quadricauda was exposed to PFOA, the fatty acid methyl ester yield increased by 178 % through transesterification. The transcriptome analysis revealed key functional genes involved in defense, energy production, and degradation in response to PFOA exposure. These results underscore the need to develop microalgae-mediated bioremediation technology for effectively removing PFOA from polluted aquatic environments.

Overexpression of Plastid Acetyl-CoA Carboxylase Confers Stress Tolerances with Increased Levels of Unsaturated Fatty Acids in the Marine Diatom Phaeodactylum tricornutum

Acetyl-coenzyme A carboxylases (ACCs) catalyze the initial reaction of fatty acid (FA) biosynthesis. The marine diatom Phaeodactylum tricornutum has two nuclear-encoded ACCs (PtACC1 (Phatr3_EG01955) and PtACC2 (Phatr3_J55209)), both which are homomeric and predicted to be localized in the plastids and the cytosol, respectively. In this study, we focused on stromal ACC1 by constructing P. tricornutum strains expressing GFP-tagged PtACC1 (ACCG strains) and confirmed that PtACC1 was localized in or around the pyrenoid. Here, we showed that unsaturated FAs (UFAs) composing the thylakoid membrane lipids increased in PtACC1 strains grown under high light conditions (190 µmol photons m-2 s-1), and that the content of triacylglycerol (TAG) and unsaturation ratios in TAG increased under oxidative stresses (with added 50 µM H2O2). ACCG strains showed faster growth rates than wild type under high light and/or oxidative stress conditions. These results suggest that cell proliferation is maintained by an accelerated recovery of PSII due to the increased UFAs in the thylakoid membrane in ACCG strains grown in high light, and that increased UFAs in ACCG cells enhanced the tolerance to oxidative stresses presumably due to the increased scavenging capacity of UFAs against reactive oxygen species. The introduction of plastidic ACC resulted in stimulating supply of UFAs to specific lipids that in turn enhanced tolerance to various stresses.

Plastics aplenty in paddy lands: incidence of microplastics in Indian rice fields and ecotoxicity on paddy field phytoplankton

Occurrence of microplastics (MP) in natural paddy fields and its impact are less studied. This study reports the abundance of MP in two paddy fields of Kerala, India, cultivating rice crops, 'Pokkali' and 'Uma' crops, which are vital to Kerala's food security and climate resilience. Fourier transform infrared spectroscopy (FTIR) analyses confirmed the presence of polyethylene (PE) and polypropylene (PP) fragments as major MP in the surface water of paddy fields during vegetative (transplantation) and ripening (near harvesting) phases. MP density in the vegetative phase of 'Pokkali' (1370 ± 468.51 fragments/m3) and 'Uma' (1110 ± 304.96 fragments/m3) was thrice more than the ripening phase concentrations (400 ± 196.85 and 370 ± 57.00 fragments/m3, respectively). Subsequently, ecotoxicity of MP and plastic leachates (PL) on phytoplankton that are naturally found in rice fields was examined. Microalga, Chlorococcum sp., and cyanobacterium, Synechococcus sp., were grown in modified BG11 and BG11 media, respectively, and tested with paddy field concentrations for PE-MP and PE-PL. MP bestowed a significant hormetic effect on the specific growth rate of the microalga (121% of the control) whereas the cyanobacterial growth was negatively impacted (70% of the control). Both phytoplankton exhibited a similar response when exposed to PL, but results were neither dose-dependent nor significant. Further, increased catalase activity and compromised superoxide dismutase machinery in the cyanobacterium corroborated the toxic impact on growth (p ≤ 0.05), which indicates reactive oxygen species (ROS) generation in MP-treated groups. ROS generation indicates oxidative stress following MP exposure in the studied phytoplankton perhaps through surface contact or by leaching of toxic intermediates into the medium. The distinctive responses of paddy field phytoplankton to MP and PL stress suggest that MP pollution may enrich certain resilient species over others leading to a possible change in phytoplankton community structure. Pollution load indices suggest that even environmental concentrations of MP and PL may affect the rice productivity as paddy field phytoplankton play a significant role in sustaining and enhancing crop health. Therefore, the presence of MP at alarming concentrations in the paddy fields signifies the emergence of a global environmental and food security concern.

On how titanium dioxide nanoparticles attenuate the toxicity of mercuric chloride to Artemia salina: investigation of fatty acid composition, oxidative stress, and lipid peroxidation

Titanium dioxide nanoparticles (TiO2NPs) as an emerging pollutant in aquatic environments can interact with metals reducing or enhancing their toxicity in these environments. This study examined and compared the toxic effects of mercury ions (Hg2+ ions) on immobilization percentage, fatty acid profile, and oxidative stress of Artemia salina nauplii, individually (Hg) and simultaneously in the presence of 0.10 mg.L-1 (Hg-0.1TiO2NPs) and 1.00 mg.L-1 TiO2NPs (Hg-1TiO2NPs). The interaction between Hg2+ ions and TiO2NPs was evaluated using DLS and AAS-VGA. Simultaneous exposures exhibited an unexpected dual effect on A. salina nauplii. A synergistic effect was observed in Hg-0.1TiO2NPs, while increasing the TiO2NPs concentration in Hg-1TiO2NPs prevented the synergy of the mixture compounds offering an antagonistic effect on nauplii. This dual effect was assigned to a greater number of available active sites and agglomeration of TiO2NPs at higher concentrations. Oxidative stress and lipid peroxidation induced by Hg were diminished in Hg-1TiO2NPs in line with the immobilization results. In Hg, total amounts of saturated fatty acids (∑SFA) increased while total monounsaturated (∑MUFA) and total polyunsaturated (∑PUFA) ones decreased compared with the control. However, they showed no significant change considering the control in Hg-1TiO2NPs, again confirming the antagonistic effect on nauplii. The unsaturated to saturated fatty acids ratio decreased in both Hg and Hg-1TiO2NPs compared with the control, however, this reduction in Hg-1TiO2NPs was lower than in Hg. The present results emphasized getting a more comprehensive understanding of how TiO2NPs impact the bioavailability and toxicity of co-contaminants through their combined effects and interactions.

Physiological and transcriptomic response of dinoflagellate Gymnodinium catenatum to nitrate deficiency

The paralytic shellfish toxin producing dinoflagellate Gymnodinium catenatum is a globally distributed species and often forms massive blooms. However, the physiological and molecular responses of G. catenatum to nitrate starvation have not been thoroughly investigated. Our results showed that multiple forms of N could be utilized by G. catenatum under nitrate-deficient conditions. Nitrate deficiency adversely affected the growth, cellular Chlorophyll a (Chl a) content, and toxin production of G. catenatum. Transcriptomic analysis revealed significant down-regulation of gene expressions involved in the light reaction of photosynthesis, while genes related to fatty acids synthesis and antioxidation were significantly upregulated in the N-depleted cultures. Our results suggested that excess carbon was channeled into lipid synthesis for energy storage, and antioxidant reactions were upregulated to eliminate toxic peroxides caused by nitrate limitation. These findings highlight the adaptative strategy of G. catenatum in low-nitrate environments, which are crucial factors driving its bloom formation.

Stress-Induced Production of Bioactive Oxylipins in Marine Microalgae

Microalgae, stemming from a complex evolutionary lineage, possess a metabolic composition influenced by their evolutionary journey. They have the capacity to generate diverse polyunsaturated fatty acids (PUFAs), akin to those found in terrestrial plants and oily fish. Also, because of their numerous double bonds, these metabolic compounds are prone to oxidation processes, leading to the creation of valuable bioactive molecules called oxylipins. Moreover, owing to their adaptability across various environments, microalgae offer an intriguing avenue for biosynthesizing these compounds. Thus, modifying the culture conditions could potentially impact the profiles of oxylipins. Indeed, the accumulation of oxylipins in microalgae is subject to the influence of growth conditions, nutrient availability, and stressors, and adjusting these factors can enhance their production in microalgae culture. Consequently, the present study scrutinized the LC-MS/MS profiles of oxylipins from three marine microalgae species (two Haptagophytes and one Chlorophyte) cultivated in 1 L of photobioreactors under varying stress-inducing conditions, such as the introduction of H2O2, EtOAc, and NaCl, during their exponential growth phase. Approximately 50 oxylipins were identified, exhibiting different concentrations depending on the species and growth circumstances. This research suggests that microalgae metabolisms can be steered toward the production of bioactive oxylipins through modifications in the culture conditions. In this instance, the application of a low dose of hydrogen peroxide to Mi 124 appears to stimulate the production of nonenzymatic oxylipins. For Mi136, it is the application of salt stress that seems to increase the overall production of oxylipins. In the case of Mi 168, either a low concentration of H2O2 or a high concentration of AcOEt appears to have this effect.

Responses of Dunaliella sp. AL-1 to chromium and copper: Biochemical and physiological studies

Microalgae have gained recognition as versatile candidates for the remediation of heavy metals (HMs). This study investigated the biosorption potential of Dunaliella sp. AL1 for copper (Cu(II)) and hexavalent chromium (Cr(VI)) in aqueous solutions. The marine microalga Dunaliella sp. AL1 was exposed to half-sublethal concentrations of both metals in single and bimetallic systems, and responses in algal growth, oxidative stress, photosynthetic pigment production, and photosynthetic performance were evaluated. Cu and/or Cr exposure increased the generation of reactive oxygen species (ROS) in microalgae cells but did not impact algal growth. In terms of photosynthesis, there was a decrease in chlorophylls and carotenoids production in the microalgae culture treated with Cr, either alone or in combination with Cu. The study recorded promising metal removal efficiencies: 26.67%-20.11% for Cu and 94.99%-95.51% for Cr, in single and bimetallic systems, respectively. FTIR analysis revealed an affinity of Cu and Cr ions towards aliphatic/aldehyde C-H, N-H bending, and phosphate groups, suggesting the formation of complex bonds. Biochemical analysis of microalgae biomass collected after the removal of Cr alone or in combination with Cu showed a significant decrease in total carbohydrate content and soluble protein levels. Meanwhile, higher lipid accumulation was recorded and evidenced by BODIPY 505/515 staining. Fatty acid composition analysis by GC revealed a modulation in lipid composition, with a decrease in the ratio of unsaturated fatty acids (UFA) to saturated fatty acids (SFA), in response to Cu, Cr, and Cu-Cr exposure, indicating the suitability of the biomass for sustainable biofuel production.

Utilizing novel Aspergillus species for bio-flocculation: A cost-effective approach to harvest Scenedesmus microalgae for biofuel production

The present study aimed to isolate a bioflocculating fungal strain from wastewater collected from a local bike garage. The isolate showed maximum similarity to Aspergillus species. The fungus was identified as Aspergillus flavus species F_GTAF1 IU (accession no OP703382). The isolated fungus was evaluated in terms of biomass recovery efficiency in Scenedesmus Sp. GTAF01. The extent of algal fungal co-pelletization was evaluated as a function of the algae-to-fungi ratio, volume of fungal culture in broth, agitation rate, and pH. results showed that at fungal culture volume of 60 ░ %v/v, fungal culture volume of 1:3 ░ %w/w, 100 rpm, and pH 3, 93.6 ░ % biomass was obtained during the initial 5 h. At wavenumbers 1384 and 1024 cm-1 a significant alteration in the transmission percentage was observed in co-pellet compared to algae and fungal cells. This shows the significant role of C-H-H and C-N stretches in co-pellet formation. This study provides deep insight into effective microalgal harvesting along with the simultaneous extraction of lipids that can be used for the sustainable production of biodiesel.

Impact of the Deletion of Genes of the Nitrogen Metabolism on Triacylglycerol, Cardiolipin and Actinorhodin Biosynthesis in Streptomyces coelicolor

Since nitrogen limitation is known to be an important trigger of triacylglycerol (TAG) accumulation in most microorganisms, we first assessed the global lipid content of 21 strains derived from Streptomyces coelicolor M145 deleted for genes involved in nitrogen metabolism. Seven of these strains deleted for genes encoding proteins involved in polyamine (GlnA2/SCO2241, GlnA3/SCO6962, GlnA4/SCO1613), or protein (Pup/SCO1646) degradation, in the regulation of nitrogen metabolism (GlnE/SCO2234 and GlnK/SCO5584), or the global regulator DasR/SCO5231 that controls negatively the degradation of N-acetylglucosamine, a constituent of peptidoglycan, had a higher TAG content than the original strain, whereas five of these strains (except the glnA2 and pup mutants) had a lower cardiolipin (CL) content. The production of the blue polyketide actinorhodin (ACT) was totally abolished in the dasR mutant in both Pi conditions, whereas the deletion of pup, glnA2, glnA3, and glnA4 was correlated with a significant increase in total ACT production, but mainly in Pi limitation. Unexpectedly, ACT production was strongly reduced in the glnA3 mutant in Pi proficiency. Altogether, our data suggest that high TAG and ACT biosynthesis and low CL biosynthesis might all contribute to the lowering of oxidative stress resulting from nitrogen limitation or from other causes.

Ultrastructural changes, pigment responses and bioaccumulation in the microalga Phaeodactylum tricornutum Bohlin exposed to BPA analogues

As well-known, microalgae have a pivotal role in aquatic environments, being the primary producer. In this study, we investigated the effects of Bisphenol A (BPA) analogues on cell ultrastructure, reactive oxygen species (ROS) production and photosynthetic pigment responses in the diatom Phaeodactylum tricornutum. Microalgae were exposed during both exponential and stationary growth phases to an environmental relevant concentration (300 ng/L) of three differing BPA analogues (BPAF, BPF, and BPS) and their mixture (100 ng/L of each compound). Bioaccumulation of such compounds in microalgae was also analysed. During the stationary growth phase, a significant increase in the percentage of cells with hydrogen peroxide production was recorded after exposure to both BPS and MIX. Conversely, no significant effects on total chlorophylls and carotenoids were observed. During exponential growth phase we observed that control cultures had chloroplasts with well-organized thylakoid membranes and a central pyrenoid. On the contrary, the culture cells treated with BPA analogues and MIX showed chloroplasts characterized by evident dilation of thylakoid membranes. The presence of degeneration areas in the cytoplasm was also recorded. During the stationary growth phase, control and culture cells were characterized by chloroplasts with a regular thylakoid system, whereas BPA analogues-exposed cells were characterized by a deep degradation of the cytoplasm but showed chloroplasts without evident alterations of the thylakoid system. Lipid bodies were visible in treated microalgae. Lastly, microalgae bioaccumulated mainly BPS and BPF, alone or in the MIX. Overall, results obtained revealed that BPA analogues can affect some important biochemical and ultrastructure features of microalgae, promoting ROS production. Lastly, the capability of microalgae to bioaccumulate bisphenols suggest a potential ecotoxicological risk for filter-feeders organisms.

Micro-and nano-plastics induce kidney damage and suppression of innate immune function in zebrafish (Danio rerio) larvae

Aquatic environments serve as critical repositories for pollutants and have significantly accumulated micro- and nanoplastics (MNPs) due to the extensive production and application of plastic products. While the disease resistance and immunity of fish are closely linked to the condition of their aquatic habitats, the specific effects of nanoplastics (NPs) and microplastics (MPs) within these environments on fish immune functions are still not fully understood. The present study utilized zebrafish (Danio rerio) embryos and larvae as model organisms to examine the impacts of polystyrene NPs (100 nm) and MPs (5 μm) on fish immune responses. Our findings reveal that NPs and MPs tend to accumulate on the surfaces of embryos and within the intestines of larvae, triggering oxidative stress and significantly increasing susceptibility to Edwardsiella piscicida infection in zebrafish larvae. Transmission electron microscopy examined that both NPs and MPs inflicted damage to the kidney, an essential immune organ, with NPs predominantly inducing endoplasmic reticulum stress and MPs causing lipid accumulation. Transcriptomic analysis further demonstrated that both NPs and MPs significantly suppress the expression of key innate immune pathways, notably the C-type lectin receptor signaling pathway and the cytosolic DNA-sensing pathway. Within these pathways, the immune factor interleukin-1 beta (il1b) was consistently downregulated in both exposure groups. Furthermore, exposure to E. piscicida resulted in restricted upregulation of il1b mRNA and protein levels, likely contributing to diminished disease resistance in zebrafish larvae exposed to MNPs. Our findings suggest that NPs and MPs similarly impair the innate immune function of zebrafish larvae and weaken their disease resistance, highlighting the significant environmental threat posed by these pollutants.

Using single-species and algal communities to determine long-term adverse effects of silver nanoparticles on freshwater phytoplankton

The physical and chemical properties of silver nanoparticles (AgNPs) have led to their increasing use in various fields such as medicine, food, and industry. Evidence has proven that AgNPs cause adverse effects in aquatic ecosystems, especially when the release of Ag is prolonged in time. Several studies have shown short-term adverse effects of AgNPs on freshwater phytoplankton, but few studies have analysed the impact of long-term exposures on these populations. Our studies were carried out to assess the effects of AgNPs on growth rate, photosynthesis activity, and reactive oxygen species (ROS) generation on the freshwater green algae Scenedesmus armatus and the cyanobacteria Microcystis aeruginosa, and additionally on microcystin (MC-LR) generation from these cyanobacteria. The tests were conducted both in single-species cultures and in phytoplanktonic communities exposed to 1 ngL-1 AgNPs for 28 days. The results showed that cell growth rate of both single-species cultures decreased significantly at the beginning and progressively reached control-like values at 28 days post-exposure. This effect was similar for the community-cultured cyanobacteria, but not for the green algae, which maintained a sustained decrease in growth rate. While gross photosynthesis (Pg) increased in both strains exposed in single cultures, dark respiration (R) and net photosynthesis (Pn) decreased in S. armatus and M. aeruginosa, respectively. These effects were mitigated when both strains were exposed under community culture conditions. Similarly, the ROS generation shown by both strains exposed in single-species cultures was mitigated when exposure occurred in community cultures. MC-LR production and release were significantly decreased in both single-species and community exposures. These results can supply helpful information to further investigate the potential risks of AgNPs and ultimately help policymakers make better-informed decisions about their utilization for environmental restoration.

Unveiling the molecular networks underlying cellular impairment in Saccharomyces cerevisiae: investigating the effects of magnesium oxide nanoparticles on cell wall integrity and endoplasmic reticulum stress response

Nanoparticles, particularly magnesium oxide nanoparticles (MgO-NPs), are increasingly utilized in various fields, yet their potential impact on cellular systems remains a topic of concern. This study aimed to comprehensively investigate the molecular mechanisms underlying MgO-NP-induced cellular impairment in Saccharomyces cerevisiae, with a focus on cell wall integrity, endoplasmic reticulum (ER) stress response, mitochondrial function, lipid metabolism, autophagy, and epigenetic alterations. MgO-NPs were synthesized through a chemical reduction method, characterized for morphology, size distribution, and elemental composition. Concentration-dependent toxicity assays were conducted to evaluate the inhibitory effect on yeast growth, accompanied by propidium iodide (PI) staining to assess membrane damage. Intracellular reactive oxygen species (ROS) accumulation was measured, and chitin synthesis, indicative of cell wall perturbation, was examined along with the expression of chitin synthesis genes. Mitochondrial function was assessed through Psd1 localization, and ER structure was analyzed using dsRed-HDEL marker. The unfolded protein response (UPR) pathway activation was monitored, and lipid droplet formation and autophagy induction were investigated. Results demonstrated a dose-dependent inhibition of yeast growth by MgO-NPs, with concomitant membrane damage and ROS accumulation. Cell wall perturbation was evidenced by increased chitin synthesis and upregulation of chitin synthesis genes. MgO-NPs impaired mitochondrial function, disrupted ER structure, and activated the UPR pathway. Lipid droplet formation and autophagy were induced, indicating cellular stress responses. Additionally, MgO-NPs exhibited differential cytotoxicity on histone mutant strains, implicating specific histone residues in cellular response to nanoparticle stress. Immunoblotting revealed alterations in histone posttranslational modifications, particularly enhanced methylation of H3K4me. This study provides comprehensive insights into the multifaceted effects of MgO-NPs on S. cerevisiae, elucidating key molecular pathways involved in nanoparticle-induced cellular impairment. Understanding these mechanisms is crucial for assessing nanoparticle toxicity and developing strategies for safer nanoparticle applications.

Concentration-dependent dual roles of proanthocyanidins on oxidative stress and docosahexaenoic acid production in Schizochytrium sp. ATCC 20888

Antioxidant addition is an effective strategy to achieve docosahexaenoic acid (DHA) overproduction in oleaginous microorganisms. Nevertheless, antioxidants like phenolic compounds sometimes exert pro-oxidant activity. In this work, effects of proanthocyanidins (PAs) on fermentation performance and oxidative stress in Schizochytrium sp. were investigated. Low PAs addition (5 mg/L) reduced reactive oxygen species and enhanced lipogenic enzymes activities and NADPH, resulting in significant increase in lipid (20.3 g/L) by 33.6 % and DHA yield (9.8 g/L) by 53.4 %. In contrast, high PAs addition (500 mg/L) exerted pro-oxidant effects, aggravated oxidative damage and lipid peroxidation, leading to sharp decrease in biomass (21.3 g/L) by 35.1 %, lipid (8.2 g/L) by 46.0 %, and DHA (2.9 g/L) by 54.8 %. Therefore, the antioxidant concentration is especially crucial in DHA production. This study is the first to report concentration-dependant dual roles of PAs in oxidative stress and DHA production in Schizochytrium sp., providing new insights into microbial DHA production.

Understanding the Impact of Nitrogen Availability: A Limiting Factor for Enhancing Fucoxanthin Productivity in Microalgae Cultivation

This study aimed to investigate the regulation of fucoxanthin (FX) biosynthesis under various nitrogen conditions to optimize FX productivity in Phaeodactylum tricornutum. Apart from light, nitrogen availability significantly affects the FX production of microalgae; however, the underlying mechanism remains unclear. In batch culture, P. tricornutum was cultivated with normal (NN, 0.882 mM sodium nitrate), limited (LN, 0.22 mM), and high (HN, 8.82 mM) initial nitrogen concentrations in f/2 medium. Microalgal growth and photosynthetic pigment production were examined, and day 5 samples were subjected to fucoxanthin-chlorophyll a/c-binding protein (FCP) proteomic and transcriptomic analyses. The result demonstrated that HN promoted FX productivity by extending the exponential growth phase for higher biomass and FX accumulation stage (P1), showing a continuous increase in FX accumulation on day 6. Augmented FX biosynthesis via the upregulation of carotenogenesis could be primarily attributed to enhanced FCP formation in the thylakoid membrane. Key proteins, such as LHC3/4, LHCF8, LHCF5, and LHCF10, and key genes, such as PtPSY, PtPDS, and PtVDE, were upregulated under nitrogen repletion. Finally, the combination of low light and HN prolonged the P1 stage to day 10, resulting in maximal FX productivity to 9.82 ± 0.56 mg/L/day, demonstrating an effective strategy for enhancing FX production in microalgae cultivation.

Application of ANN-MOGA for nutrient sequestration for wastewater remediation and production of polyunsaturated fatty acid (PUFA) by Chlorella sorokiniana MSP1

Chlorella bears excellent potential in removing nutrients from industrial wastewater and lipid production enriched with polyunsaturated fatty acids. However, due to the changing nutrient dynamics of wastewater, growth and metabolic activity of Chlorella are affected. In order to sustain microalgal growth in wastewater with concomitant production of PUFA rich lipids, RSM (Response Surface Methodology) followed by heuristic hybrid computation model ANN-MOGA (Artificial Neural Network- Multi-Objective Genetic Algorithm) were implemented. Preliminary experiments conducted taking one factor at a time and design matrix of RSM with process variables viz. Sodium chloride (1 mM-40 mM), Magnesium sulphate (100 mg-800 mg) and incubation time (4th day to 20th day) were validated by ANN-MOGA. The study reported improved biomass and lipid yield by 54.25% and 12.76%, along with total nitrogen and phosphorus removal by 21.92% and 18.72% respectively using ANN-MOGA. It was evident from FAME results that there was a significantly improved concentration of linoleic acid (19.1%) and γ-linolenic acid (21.1%). Improved PUFA content makes it a potential feedstock with application in cosmeceutical, pharmaceutical and nutraceutical industry. The study further proves that C. sorokiniana MSP1 mediated industrial wastewater treatment with PUFA production is an effective way in providing environmental benefits along with value addition. Moreover, ANN-MOGA is a relevant tool that could control microalgal growth in wastewater.

Optimizing light regimes for neutral lipid accumulation in Dunaliella salina MCC 43: a study on physiological status and carbon allocation

Dunaliella salina is a favourable source of high lipid feedstock for biofuel and medicinal chemicals. Low biomass output from microalgae is a significant barrier to industrial-scale commercialisation. The current study aimed to determine how photosynthetic efficiency, carbon fixation, macromolecular synthesis, accumulation of neutral lipids, and antioxidative defence (ROS scavenging enzyme activities) of D. salina cells were affected by different light intensities (LI) (50, 100, 200, and 400 µmol m-2 s-1). The cells when exposed to strong light (400 µmol m-2 s-1) led to reduction in chlorophyll a but the carotenoid content increased by 19% in comparison to the control (LI 100). The amount of carbohydrate changed significantly under high light and in spite of stress inflicted on the cells by high irradiation, a considerable increase in activity of carbonic anhydrase and fixation rate of CO2 were recorded, thus, preserving the biomass content. The high light exposed biomass when subjected to nitrogen-deficient medium led to increase in lipid content (59.92% of the dry cell weight). However, neutral lipid made up 78.26% of the total lipid while other lipids like phospholipid and glycolipid content decreased, showing that the lipid was redistributed in these cells under nitrogen deprivation, making the organism more appropriate for biodiesel/jet fuel use. Although D. salina cells had a relatively longer generation time (3.5 d) than other microalgal cells, an economic analysis concluded that the amount of carotenoid they produced and the quality of their lipids made them more suited for commercialization.

Comparative toxicity assessment of individual, binary and ternary mixtures of SiO2, Fe3O4, and ZnO nanoparticles in freshwater microalgae, Scenedesmus obliquus: Exploring the role of dissolved ions

Metal oxide nanoparticles (NPs) are considered among the most prevalent engineered nanomaterials. To have a deeper understanding of the mode of action of multiple metal oxide nanoparticles in mixtures, we have used a unicellular freshwater microalga Scenedesmus obliquus as a model organism. The toxicity of silicon dioxide (SiO2), iron oxide (Fe3O4), and zinc oxide (ZnO) NPs was studied individually as well as in their binary (SiO2 + Fe3O4, Fe3O4 + ZnO, and ZnO + SiO2) and ternary (SiO2 + Fe3O4 + ZnO) combinations. The effects of metal ions from ZnO and Fe3O4 were investigated as well. The results observed from the study, showed that a significant amount of toxicity was contributed by the dissolved ions in the mixtures of the nanoparticles. Decreases in the cell viability, ROS generation, lipid peroxidation, antioxidant enzyme activity, and photosynthetic efficiency were analyzed. Among all the individual particles, ZnO NPs showed the maximum effects and increased the toxicities of the binary mixtures. The binary and ternary mixtures of the NPs clearly showed increased toxic effects in comparison with the individual entities. However, the ternary combination had lesser toxic effects than the binary combination of Fe3O4 + ZnO. The decline in cell viability and photosynthetic efficiency were strongly correlated with various oxidative stress biomarkers emphasizing the crucial role of reactive oxygen species in inducing the toxic effects. The findings from this study highlight the importance of evaluating the combinatorial effects of various metal oxide NPs as part of a comprehensive ecotoxicity assessment in freshwater microalgae.

Understanding the dynamics of Microcystis bloom: Unraveling the influence of suspended solids through proteomics and metabolomics approaches

Light plays a crucial role in blue-green algae bloom formation in lakes, while suspended solids (SS) influence underwater light intensity. This study investigates the integrated effects of SS concentrations (0-125 mg/L) on Microcystis aeruginosa in natural conditions. Results show that SS inhibits cyanobacterial growth above 100 mg/L, with 25-75 mg/L favoring bloom formation. Proteomic analysis reveals differential protein involvement in ribosomes, ABC transporters, cofactor biosynthesis, and photosynthesis pathways at 25 mg/L SS. SS concentrations within the range of 25-125 mg/L significantly impact the metabolism of algal cells, resulting in an increase in lipid metabolism and a decrease in the biosynthesis of secondary metabolites in cyanobacteria. These coordinated biochemical adaptations play a vital role in the survival of cyanobacteria in challenging environmental conditions. Employing a multi-omics approach enhances our comprehension of how M. aeruginosa responds to SS and the underlying molecular mechanisms, thereby contributing to our understanding of cyanobacteria outbreaks. This underscores the importance of monitoring SS concentrations in lakes as a proactive measure for future control of cyanobacteria dominance.

The impact of light/dark regimes on structure and physiology of Chlorella vulgaris biofilms

Introduction

Biofilm-based microalgae production technologies offer enormous potential for improving sustainability and productivity. However, the light pattern induced by these technologies is a key concern for optimization.

Methods

In this work, the effects of light/dark cycles on architecture, growth, and physiology of Chlorella vulgaris biofilms were assessed in a millifluidic flow-cell with different time cycles (15 s to 3 min) keeping the average light constant at 100 μmol·m-2·s-1.

Results and discussion

Results showed that photoinhibition can be mitigated by applying a light fraction of 1/3 and a cycle time of 15 s. By contrast, when the cycle time is extended to 90 s and 3 min, photoinhibition is high and photoefficiency dramatically decreases. To cope with light stress, cells acclimate and organize themselves differently in space. A high peak light (500 μmol·m-2·s-1) triggers a stress, reducing cell division and inducing clusters in the biofilm. This work provides guidelines for optimizing rotating microalgae production systems in biofilms and assesses the minimum rotating frequency required to maintain the net growth rate close to that of continuous light of the same average intensity, mitigating photo-inhibition. The overall gain in productivity is then provided by the total surface of the biofilm turning in the illuminated surface area.

Strategies of NaCl Tolerance in Saline-Alkali-Tolerant Green Microalga Monoraphidium dybowskii LB50

Studying how freshwater cells modify metabolism and membrane lipids in response to salt stress is important for understanding how freshwater organisms adapt to salt stress and investigating new osmoregulatory ways. Physiological, biochemical, metabolic, and proteomic analyses were applied in a novel saline-alkali-tolerant microalga Monoraphidium dybowskii LB50 under different NaCl concentrations. Cells adopt a variety of strategies to adapt to salt stress, including increasing ion transport and osmolytes, regulating cell cycle and life history, and accumulating triacylglycerol (TAG). A large number of metabolic activities point to TAG accumulation. With increasing NaCl concentration, the C resource for TAG accumulation went from photosynthetically fixed C and a small amount of lipid remodeling to macromolecule degradation and a mass of lipid remodeling, respectively. The energy for TAG accumulation went from linear electron transfer and oxidative phosphate pentose pathway to cyclic electron flow, substrate phosphorylation, oxidation phosphorylation, and FA oxidation. Additionally, digalacturonic acid and amino acids of the N-acetyl group, which usually were the osmotica for marine organisms, were important for M. dybowskii LB50. Freshwater organisms evolved many biological ways to adapt to salt stress. This insight enriches our understanding of the adaptation mechanisms underlying abiotic stress.

Effects of low temperature and highlight stress on lipid accumulation and cell structure of Tropidoneis maxima

Tropidoneis maxima is a marine diatom with a rapid growth rate that produces high levels of lipids. To explore whether the lipid content could be further enhanced, cultures were first incubated under optimal conditions and then stressed under low temperature (10°C), a high light intensity level (80 μmol/m2 ·s), and the two factors together (interaction treatment). The results indicated that high light intensity and the temperature-light interaction exhibited greater impacts on lipid synthesis of T. maxima than low temperature. The two stress treatments increased lipid content by 17.16% and 16.6% compared to the control. In particular, higher biomass concentration was obtained with high light intensity (1.082 g L-1 ) and low temperature (1.026 g L-1 ). Moreover, high light intensity (9.06%) and interaction (10.3%) treatments yielded lower starch content compared to low temperature (14.27%) at the end of the stress culture. After 3 days of stress culture, the high light intensity treatment resulted in a 97.01% increase in cell wall thickness and an 18.46% decrease in cell diameter. The results suggest that high light intensity stress on T. maxima would open a new approach to cost-effective biolipid production.

Effects of o-cresol on the growth and biochemical compositions in marine microalgae

To assess the toxic effects of o-cresol on marine organisms, Skeletonema costatum and Phaeodactylum tricornutum were chosen as test subjects to investigate its impact on growth and biochemical compositions. The results indicated that the 96-h EC50 values for o-cresol in S. costatum and P. tricornutum were 7.99 mg/L and 13.28 mg/L, respectively, demonstrating a moderate and slight toxicity level. Conversely, the maximum no-effect concentration (NOEC) for o-cresol in S. costatum and P. tricornutum were 2.43 mg/L and 0.43 mg/L, respectively, classifying their chronic toxicity grades as negligible and low toxic. Following a 96-h exposure period, the content of photosynthetic pigments in S. costatum did not significantly differ from the control group (P > 0.05). Conversely, the levels of total protein, total lipid, and carbohydrate in microalgae were significantly induced (P < 0.05) as the concentration of o-cresol increased. Higher concentrations of o-cresol generally stimulated the synthesis of biochemical compositions in algae cells, which serves as an active defense mechanism in response to pollution stress. To comprehensively evaluate the potential risk of o-cresol to marine ecosystems, it is crucial to strengthen its toxicity studies on marine fish and crustaceans in the future.

Solar Salterns and Pollution: Valorization of Some Endemic Species as Sentinels in Ecotoxicology

Solar salterns and salt marshes are unique ecosystems with special physicochemical features and characteristic biota. Currently, there are very few studies focused on the impacts of pollution on these economic and ecological systems. Unfortunately, diversified pollution (metals, Polycyclic Aromatic Hydrocarbons, etc.) has been detected in these complex ecosystems. These hypersaline environments are under increasing threat due to anthropogenic pressures. Despite this, they represent a valuable source of microbial diversity, with taxa displaying special features in terms of environmental remediation capacities as well as economical species such as Artemia spp. (Branchiopoda) and Dunaliella salina (Chlorophyta). In this review, we discuss the impacts of pollution on these semi-artificial systems. Therefore, we have indicated the sentinel species identified in plankton communities, which can be used in ecotoxicological investigations in solar salterns. In future, researchers should increase their interest in pollution assessment in solar salterns and salt marshes.

Potential use of saline resources for biofuel production using halophytes and marine algae: prospects and pitfalls

There exists a global challenge of feeding the growing human population of the world and supplying its energy needs without exhausting global resources. This challenge includes the competition for biomass between food and fuel production. The aim of this paper is to review to what extent the biomass of plants growing under hostile conditions and on marginal lands could ease that competition. Biomass from salt-tolerant algae and halophytes has shown potential for bioenergy production on salt-affected soils. Halophytes and algae could provide a bio-based source for lignoceelusic biomass and fatty acids or an alternative for edible biomass currently produced using fresh water and agricultural lands. The present paper provides an overview of the opportunities and challenges in the development of alternative fuels from halophytes and algae. Halophytes grown on marginal and degraded lands using saline water offer an additional material for commercial-scale biofuel production, especially bioethanol. At the same time, suitable strains of microalgae cultured under saline conditions can be a particularly good source of biodiesel, although the efficiency of their mass-scale biomass production is still a concern in relation to environmental protection. This review summaries the pitfalls and precautions for producing biomass in a way that limits environmental hazards and harms for coastal ecosystems. Some new algal and halophytic species with great potential as sources of bioenergy are highlighted.

Bioaccumulation of selenium in halotolerant microalga Dunaliella salina and its impact on photosynthesis, reactive oxygen species, antioxidative enzymes, and neutral lipids

Selenium (Se) is an essential element for living systems, however, toxic at higher levels. In the present study, Dunaliella salina cells were exposed to different Se concentrations for their growth (EC₅₀ 195 mg L-¹) as well as Se accumulation. The cells exposed to 50 mg L-¹ Se showed photoautotrophic growth parallel to control and accumulated 65 μg Se g-¹ DW. A decrease in photosynthetic quantum yield, chlorophyll content, and the increase in intracellular reactive oxygen species, proline content, and lipid peroxidation accompanied by higher neutral lipid accumulation, were recorded at higher Se level. The enzymes superoxide dismutase and catalase played a pivotal role in antioxidative defense. Heterogeneity in accumulated carotenoids at varying concentrations of selenium was prevalent. The cells exposed to 200 mg L-¹ Se resulted in the disorganization of organelles. Thus, the Se enriched biomass obtained at 50 mg L-¹ may be explored for bio-fortification of food and feed.

Evaluation of Shifts of Gene Transcription Levels of Unicellular Green Alga Chlamydomonas reinhardtii Due to UV-C Irradiation

Green algae produce valuable lipids as carbon-recycling resources. Collecting whole cells with the intracellular lipids could be efficient without cell burst; however, direct use of the cells causes microbial contamination in environments. Then, UV-C irradiation was selected to satisfy the requirements of avoiding the cell burst and sterilizing cells with Chlamydomonas reinhardtii. UV-C irradiation with 1.209 mW·cm−2 showed enough sterilization activity for 1.6 × 107 cells·mL−1 of C. reinhardtii in a depth of 5 mm for 10 min. The irradiation showed no effects to composition and contents of the intracellular lipids. From the viewpoint of transcriptomic analysis, the irradiation displayed possibilities of (i) inhibition of the synthesis of lipids due to decrement of the transcription of related genes, such as diacylglycerol acyl transferase and cyclopropane fatty acid synthase, and (ii) activation of lipid degradation and the production of NADH2+ and FADH2 due to increment of the transcription of related genes, such as isocitrate dehydrogenase, dihydrolipoamide dehydrogenase and malate dehydrogenase. Irradiation until cell death could be insufficient to shift the metabolic flows even though the transcriptions were already shifted to lipid degradation and energy production. This paper is the first report of the response of C. reinhardtii to UV-C irradiation on the transcription level.

Metabolomic response of microalgae towards diclofenac sodium during its removal from water and concomitant recovery of pigments and lipids

The aim of this work was to assess the efficiency of freshwater green microalga, Chlorella sorokiniana for diclofenac sodium (DFS) removal, and metabolic response of alga to comprehend the metabolic pathways involved/affected during DFS decontamination. Results showed 91.51 % removal of DFS could be achieved within 9 days of algal treatment along with recovery of enhanced value-added bioresources i.e. chlorophyll, carotenoids, and lipids from the spent biomass. DFS also had an effect on enzyme activity including superoxide dismutase (SOD), catalase (CAT), and lipid peroxidation (MDA). Furthermore, metabolomics profiling provided an in-depth insight into changes in the metabolic response of C. sorokiniana wherein DFS induced 32 metabolites in microalgae compared to unexposed-control. This study offers microalgae as a green option for DFS removal, and the metabolomics study complemented with DFS could be an approach to understand the stress-induced strategies of C. sorokiniana for concomitant value-added products recovery in presence of DFS.

Enhancing the thermotolerance and erythritol production of Yarrowia lipolytica by introducing heat-resistant devices

Yarrowia lipolytica has been widely used in the food biotech-related industry, where it plays the host's role in producing erythritol. Nevertheless, a temperature of about 28°C-30°C has been estimated as the yeast's optimal growth temperature, leading to the consumption of a considerable quantity of cooling water, especially in summer, which is obligatory for fermentation. Herein is described a method for improving the thermotolerance and erythritol production efficiency at high temperatures of Y. lipolytica. Through screening and testing different heat resistant devices, eight refactored engineered strains showed better growth at higher temperature and the antioxidant properties of the eight engineered strains were also improved. In addition, the erythritol titer, yield and productivity of the strain FOS11-Ctt1 represented the best among the eight strains, reaching at 39.25 g/L, 0.348 g/g glucose, and 0.55 g/L/h respectively, which were increased by 156%, 86% and 161% compared with the control strain, respectively. This study provides insight into an effective heat-resistant device that could enhance the thermotolerance and erythritol production of Y. lipolytica, which might be considered a valued scientific reference for other resistant strains' construction.

Toxicity of boron nitride nanoparticles influencing bio-physicochemical responses in freshwater green algae

Boron nanoparticles have emerged as promising nanomaterials with a wide array of applications in the biomedical, industrial, and environmental fields. However, the potential impact of these nanoparticles on aquatic organisms is not yet known. In the present study, the comparative impact of boron nitride nanoparticles and its bulk form is investigated on two freshwater algae. For this purpose, the effect on the physiological index, cellular morphology, and biochemistry profiles are examined. In Chlorella vulgaris, nano form of boron nitride is found to reduce the growth more (40%) than its bulk form (with ~ 25% growth reduction) at 50 mgl^-1 treatment level. While in case of Coelastrella terrestris, 40% reduction under nano form and 33.33% reduction under bulk form is observed at 100 mgl^-1 of boron nitride. Chlorophyll and carotenoid levels were also reduced under nanoparticles compared to the bulk. Proline, lactate dehydrogenase, and malondialdehyde assay were found significantly high under nanoparticle exposure. Additionally, increased catalase and superoxide dismutase enzyme activity under nanoparticle exposure revealed that the antioxidant system was activated in both the algae to eliminate the adverse influence of reactive oxygen species. The shading effect and aggregation of nanoparticles over the surface of algal cells are also important factors in attributing toxicity which are confirmed through the compound, TEM, and SEM micrographs. The study suggests that the nano form is more toxic than the bulk form and toxicity is concentration-dependent.

Mixotrophic culture of bait microalgae for biomass and nutrients accumulation and their synergistic carbon metabolism

Microalgae cannot meet the bait demand for aquaculture due to light intensity limitation and other disadvantageous conditions. This research selected 6 mixotrophic microalgae, and the optimal strains and organic carbon were screened. The results showed that Thalassiosira pseudonana and Chlorella sp. are suitable for mixotrophic culture. The maximum cell density of Thalassiosira pseudonana was found to be 1.67 times than that of the photoautotrophic group when glycerol was added. The maximum cell density of Chlorella sp. with acetic acid was 1.69 times than that of the photoautotrophic group. When the concentration of acetic acid was 5.0 g·L^-1 and the concentration of KNO₃ was 0.2 g·L^-1, the maximum biomass of Chlorella sp. could reach 3.54 × 10⁷ cells·mL^-1; the maximum biomass of Thalassiosira pseudonana was 5.53 × 10⁶ cells·mL^-1 with 10.0 g·L^-1 glycerol and 0.2 g·L^-1 KNO₃. Metabolomic analysis further revealed that mixotrophic bait microalgae could promote the accumulation of lipids and amino acids.

Asterarcys quadricellulare (Chlorophyceae) protects H9c2 cardiomyoblasts from H2O2-induced oxidative stress

Oxidative stress has recently been identified as an important mediator of cardiovascular diseases. The need to find efficient antioxidant molecules is essential in the disease's prevention. Therefore, the present study aimed to evaluate the potential of microalgae bioactive in protecting H9c2 cardiomyoblasts from H₂O₂-induced oxidative stress. Four microalgal species were investigated for their antioxidant capacity. A qualitative assessment of oxidative stress in H9c2 cardiomyoblasts stained with DCFH-DA, treated with the highly active microalgae extracts, was performed. The protein expression of total caspase-3 was also examined to investigate whether the extract protects H9c2 cardimyoblasts from H₂O₂-induced apoptosis. High antioxidant activity was observed for the hexanoic extracts after 10 days of cultivation. Asterarcys quadricellulare exhibited the highest antioxidant capacity of 110.59 ± 1.75 mg TE g^-1 dry weight and was tested against H9c2 cardiomyoblasts, which were initially subjected to H₂O₂-induced oxidative stress. This hexanoic extract protected against H₂O₂ induced oxidative stress with a similar scavenging capacity as N-Acetylcysteine. Furthermore, total caspase-3 was increased following treatment with the hexanoic extract, suggesting that A. quadricellulare also had anti-apoptotic properties. The outcome of our study highlighted the possible use of the local A. quadricellulare strain QUCCCM10 as a natural, safe, and efficient antioxidant to prevent cardiovascular diseases.

Modulation of the metabolite content of the unicellular rhodophyte Porphyridium purpureum using a 2-stage cultivation approach and chemical stressors

There have been growing interests in microalgal biotechnology for the biorefining of bioactive compounds such as carotenoid pigments, ω-3 fatty acids, antioxidants or antimicrobials for sectoral applications in the pharmacology, nutraceutical and cosmetic fields. This study focused on the unicellular marine rhodophyte Porphyridium purpureum CCAP 1380/1 A, which was cultivated via a two-stage batch growth mode for 10 days using hydrogen peroxide (H₂O₂), the phytohormone methyl jasmonate (MJ) and three plant extracts (Passiflora incarnata, Panax ginseng and Valeriana officinalis). The microalgal biomass was then analysed for its protein, phycoerythtin, carbohydrate and pigment composition together with its pigment content and antioxidant activity. Of note, MJ increased the protein and phycoerythtin content (up to 225 µg BSA eq./mg DW and 15 mg/ml, respectively) while both the MJ and H₂O₂ treatments increased carotenoid pigment yields (β-carotene and zeaxanthin, up to 5 and 4 mg/g, respectively). Carbohydrates were enhanced ∼10 fold by the Valeriana officinalis treatment (up 192 μg starch eq./mg). Overall, neutral lipids and antioxidants were mostly negatively affected by the plant extracts. The greatest antioxidant activity registered was obtained with the H₂O₂ treatment (15 μmol Trolox eq./g DW with TEAC assay). P. purpureum contains multiple valuable compounds of commercial interest. These results indicate that they can be favorably modulated using specific cultivation regimes and chemical enhancers, thereby facilitating the exploitation of the biomass by applying a suitable co-refinery pipeline.

Humic Acid Alleviates the Toxicity of Nanoplastics towards Solanum lycopersicum

Nanoplastics (NPs) are emerging pollutants that contaminate agricultural produce. The present study investigates the impact of polystyrene (PS) and humic acid (HA) individually and in combination on the germination and growth of seeds of Solanum lycopersicum (tomato). Here we report the formation of eco-corona upon the interaction of PS with humic acid at 24 h with a significant increase in hydrodynamic size. Seed germination, plant growth, and chlorophyll content increased in the coronated PS. In addition, we report that the treatment of seeds with PS + HA resulted in the germination of 90% of seeds, while treatment with only PS resulted in the germination of only 65.8% of seeds. A quantitative analysis of chlorophyll (a, b, and a + b) revealed that HA-treated groups and PS + HA-treated groups showed significantly high chlorophyll (a, b, and a + b) contents of (PS: 3.48 mg g−1, 2.12 mg g−1, and 4.19 mg g−1, HA: 5.76 mg g−1, 3.88 mg g−1, and 6.41 mg g−1, PS + HA: 4.17 mg g−1, 3.23 mg g−1, and 6.58 mg g−1)respectively compared to PS treated groups. Similarly, ROS levels were comparatively low in HA and PS + HA-treated groups than in only-PS-treated groups. Furthermore, we observed a decline in the level of antioxidant enzyme (superoxide dismutase and catalase) activity in HA and PS + HA treated groups than that in only-PS treated groups. The results indicate that HA significantly reduces PS-induced toxicity and improves germination and growth of seeds of Solanum lycopersicum; the corresponding reduction in toxic effects may be due to eco-corona formation on the PS. We understand that eco-corona is a way to protect plants from xenobiotics concerning nanoplastics.

The Effect of Humic Acid and Polystyrene Fluorescence Nanoplastics on Solanum lycopersicum Environmental Behavior and Phytotoxicity

The impacts of nanoplastics (100 nm) on terrestrial systems are unclear at this time. Due to the utilization of sewage sludge, plastic particles are likely to accumulate in these systems. The current research investigates how Solanum lycopersicum seed germination and growth are affected by fluorescence polystyrene (Flu-PS), humic acid (HA), and a Flu-PS+HA combination (tomato). Following 24 h of interaction between Flu-PS and HA, our report details the development of an eco-corona with a significant increase in hydrodynamic size. Plant growth, seed germination, and chlorophyll content were all enhanced by the eco-coronated Flu-PS.Additionally, we discover that seeds treated with Flu-PS+HA demonstrated a germination rate of 90%, compared to just 65.8% for seeds treated with Flu-PS alone. Chlorophyll (a, b, and a + b) content measurements indicated that HA-treated groups and Flu-PS+HA-treated groups had considerably higher levels of chlorophyll (a, b, and a + b) than Flu-PS-treated groups (Flu-PS: 3.18 mg g-1, 2.12 mg g-1, and 3.89 mg g-1, HA: 5.96 mg g-1, 4.28 mg g-1, and 6.36 mg g-1, and Flu-PS+HA: 4.17 mg g-1, 3.01 mg g-1, and 6.08 mg g-1, respectively). In a similar manner, the HA and Flu-PS+HA treatment groups showed lower ROS levels than the Flu-PS treatment groups. In addition, we discovered that the activity of the antioxidant enzymes superoxide dismutase and catalase was lower in the groups treated with HA and Flu-PS+HA than in the groups solely treated with Flu-PS. The results demonstrated that HA significantly lessens the toxicity caused by Flu-PS, while also promoting the germination and growth of Solanum lycopersicum seeds. The related decrease in toxic effects may be ascribed to the establishment of an eco-corona on the Flu-PS. We think that the use of eco-coronas is a technique for safeguarding plants against xenobiotics such as nanoplastics.

Physiological and proteomic responses of Chlamydomonas reinhardtii to arsenate and lead mixtures

Arsenic (As) and lead (Pb) are frequently emitted from various sources into environment, but microbial responses to their combined toxicity have not been systematically investigated. In this study, Chlamydomonas reinhardtii was exposed to two levels of arsenate (As (V), 50, 500 μg/L), Pb (II) (500, 5000 μg/L) and their mixture (50 μg/L As (V) + 500 μg/L Pb (II); 500 μg/L As (V) + 5000 μg/L Pb (II)). The growth of C. reinhardtii was inhibited more remarkably by As (V) than by Pb (II). The As stress was alleviated by Pb in the 50 μg/L As (V) + 500 μg/L Pb (II) treatment, but was enhanced upon the 500 μg/L As (V) + 5000 μg/L Pb (II) exposure, with more pronounced changes in a number of physiological parameters of the algal cells. Proteomic results showed that 71 differently expressed proteins (DEPs) in the treatment of 50 μg/L As (V) + 500 μg/L Pb (II), and 167 DEPs were identified in that of 500 μg/L As (V) + 5000 μg/L Pb (II). These proteins were involved in energy metabolism, photosynthetic carbon fixation, reactive oxygen scavenging and defense, and amino acid synthesis. Taken together, these physiological and proteomic data demonstrated that C. reinhardtii could resist the As (V) and Pb (II) combined treatments through extracellular complexation and intracellular pathways.

Changes in Carbon Partitioning and Pattern of Antioxidant Enzyme Activity Induced by Arginine Treatment in the Green Microalga Dunaliella salina Under Long-Term Salinity

In this work, the effects of arginine (Arg) on biochemical responses and antioxidant enzyme activity in the green microalga Dunaliella salina grown at different salt concentrations were investigated. Suspensions adapted with the concentrations of 1, 2, and 3 M NaCl were treated at the exponential growth phase with a concentration of 5 mM Arg. Salt stress was associated with a large decrease in the number of cells and non-reducing sugar levels but accumulated higher amounts of chlorophyll, β-carotene, reducing sugar, starch, total protein, free amino acid, and glycerol. Increased levels of protein carbonylation, lipid peroxidation, proteolysis, hydrogen peroxide, and antioxidant enzyme activity also occurred during salinity. Arg treatment changed the pattern of biochemical responses in the cells grown at high salinity by directing carbon flow to the biosynthesis of non-reducing sugars instead of starch, lowering levels of hydrogen peroxide, and downregulating antioxidant enzyme activity, but the levels of lipid peroxidation, glycerol, and β-carotene remained nearly unchanged. These results suggest that Arg treatment alleviates salinity-induced oxidative stress in D. salina cells by modifying carbon partitioning and inducing signaling molecules rather than antioxidant enzymes.

Nanoplastics enhance the toxic effects of titanium dioxide nanoparticle in freshwater algae Scenedesmus obliquus

The increased usage of titanium dioxide nanoparticles (nTiO2) in consumer products has led to their prevalence in freshwater systems. Nanoplastics, a secondary pollutant, can significantly influence the toxic effects of nTiO2 in freshwater organisms. The present study investigates the role of fluorescent nanoplastics (FNPs) in modifying the harmful effects of P25 nTiO2 in freshwater algae Scenedesmus obliquus. Three different concentrations of nTiO2, 0.025, 0.25, and 2.5 mg/L, were mixed with 1 mg/L of the FNPs to perform the mixture toxicity experiments. The presence of the FNPs in the mixture increased the toxicity of nTiO2 significantly. A significant increment in the oxidative stress parameters like total ROS, superoxide (O2∎-), and hydroxyl radical generation was observed for the mixture of nTiO2 with the FNPs in comparison with their individual counterparts. The lipid peroxidation, and the antioxidant enzyme activities in the algal cells correlated well with the reactive species generation results. The treatments with the binary mixture resulted in notable decrease in the esterase activity in the algal cells. The mixture toxicity results were further validated with Abbott's independent action model. Additionally, optical microscopic analysis and FTIR analysis were performed to study the morphological and surface chemical changes in the algae. This study demonstrated that the FNPs played a key role in enhancing the toxicity of nTiO2 in freshwater algae.

Visualising the Emerging Platform of Using Microalgae as a Sustainable Bio-Factory for Healthy Lipid Production through Biocompatible AIE Probes

Nowadays, a particular focus is using microalgae to get high-valued health beneficiary lipids. The precise localisation of the lipid droplets (LDs) and biochemical changes are crucial to portray the lipid production strategy in algae, but it requires an in vivo tool to rapidly visualise LD distribution. As a novel strategy, this study focuses on detecting lipid bioaccumulation in a green microalga, Chlamydomonas reinhardtii using the aggregation-induced emission (AIE) based probe, 2-DPAN (C24H18N2O). As the messenger molecule and stress biomarker, hydrogen peroxide (H2O2) activity was detected in lipid synthesis with the AIE probe, TPE-BO (C38H42B2O4). Distinctive LDs labelled with 2-DPAN have elucidated the lipid inducing conditions, where more health beneficiary α-linolenic acid has been produced. TPE-BO labelled H2O2 have clarified the involvement of H2O2 during lipid biogenesis. The co-staining procedure with traditional green BODIPY dye and red chlorophyll indicates that 2-DPAN is suitable for multicolour LD imaging. Compared with BODIPY, 2-DPAN was an efficient sample preparation technique without the washing procedure. Thus, 2-DPAN could improve traditional fluorescent probes currently used for lipid imaging. In addition, the rapid, wash-free, multicolour AIE-based in vivo probe in the study of LDs with 2-DPAN could advance the research of lipid production in microalgae.

Ameliorating Effect of Bicarbonate on Salinity Induced Changes in the Growth, Nutrient Status, Cell Constituents and Photosynthetic Attributes of Microalga Chlorella vulgaris

The cells of Chlorella vulgaris exhibited NaCl (0-400 mM) induced decrease in the growth, protein, chlorophyll, carbohydrate and total organic carbon, whereas total lipid and proline content increased with rising level of NaCl. Addition of NaHCO₃ (20 mM) exhibited antagonistic effect against the adverse effect of salinity on the growth, level of macromolecules except proline. The SEM-EDS analysis of NaCl treated cells exhibited morphological variations as well as reduced accumulation of Na and Cl due to the presence of NaHCO₃. The results on chlorophyll fluorescence induction kinetics revealed NaCl induced decline in the photosynthetic performance and quantum yield, while non-photochemical quenching of chlorophyll was enhanced, particularly at lower concentrations of NaCl. Addition of NaHCO₃ to NaCl treated cells exhibited further increase in the non-photochemical quenching values. Thus, these results demonstrated that adverse impact of NaCl on the C. vulgaris cells was significantly mitigated in the presence of bicarbonate.

Selenite as a Lipid Inductor in Marine Microalga Dunaliella tertiolecta: Comparison of One-Stage and Two-Stage Cultivation Strategies

Microalgae have emerged as one of the most promising alternative sources of biofuels due to their high lipid accumulation ability. High lipid content is of pivotal importance for biodiesel production. In order to obtain high lipid content, modifications of culture conditions and development of an efficient lipid induction method are called for. In the present study, the possibility of using selenium in a form of sodium selenite as a lipid inductor in marine microalga Dunaliella tertiolecta was investigated during one- and two-stage cultivation modes. The effects of selenite on algal growth, pigment content, oxidative stress, and neutral lipid content were determined during both cultivation modes. The results revealed that the two-stage cultivation on 10.00-40.00 mg L-1 of selenite resulted in up to twofold higher algal cell density compared to the one-stage cultivation. Selenite concentrations from 2.50 to 20.00 mg L-1 increased lipid peroxidation during both cultivation modes, emphasizing the selenite-induced oxidative stress accompanied by the increased lipid accumulation in microalgae cells. During one- and two-stage cultivation on 20.00 mg L-1 of selenite, lipid content increased 2.39- and 5.73-fold at days 9 and 14 of cultivation, respectively. Moreover, the highest obtained neutral lipid content during the two-stage cultivation was 5.40-fold higher than lipid content obtained during the one-stage cultivation. Collectively, these results suggest that the two-stage cultivation strategy, initiated with optimal culture conditions for biomass production and followed by the addition of selenite as a stress inductor, can be successfully deployed to enhance the lipid content in D. tertiolecta.

Oxidative Stress Is a Key Modulator in the Development of Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease worldwide, and scientific studies consistently report that NAFLD development can be accelerated by oxidative stress. Oxidative stress can induce the progression of NAFLD to NASH by stimulating Kupffer cells, hepatic stellate cells, and hepatocytes. Therefore, studies are underway to identify the role of antioxidants in the treatment of NAFLD. In this review, we have summarized the origins of reactive oxygen species (ROS) in cells, the relationship between ROS and NAFLD, and have discussed the use of antioxidants as therapeutic agents for NAFLD.

Microalgae-Derived Health Supplements to Therapeutic Shifts: Redox-Based Study Opportunities with AIE-Based Technologies

Reactive oxygen species (ROS) are highly reactive molecules, serve the normal signaling in different cell types. Targeting ROS as the chemical signals, different stress based strategies have been developed to synthesis different anti-inflammatory molecules in microalgae. These molecules could be utilized as health supplements in human. To provoke the ROS-mediated defence systems, their connotation with the associated conditions must be well understood, therefore, proper tools for studying ROS in natural state are essential. The in vivo detection of ROS with phosphorescent probes offers promising opportunities to study these molecules in a non-invasive manner. Most of the common problems in the traditional fluorescent probes are lower photostability, excitation intensity, slow responsiveness, and the microenvironment that challenge their performance. Some ROS-specific aggregationinduced emission luminogens (AIEgens) with pronounced spatial and temporal resolution have recently demonstrated high selectivity, rapid responsiveness, and efficacies to resolve the aggregation-caused quenching issues. The nanocomposites of some AIE-photosensitizers can also improve the ROS-mediated photodynamic therapy. These AIEgens could be used to induce bioactive components in microalgae through altering the ROS signaling, therefore are more auspicious for biomedical research. This study reviews the prospects of AIEgen-based technologies to understand the ROS mediated bio-physiological processes in microalgae for better healthcare benefits.

Elucidating the bioremediation mechanism of Scenedesmus sp. IITRIND2 under cadmium stress

Cadmium (Cd) is a non-biodegradable pollutant that has become a global threat due to its bioaccumulation and biomagnification in higher trophic levels of the food chain. Green technologies such as phycoremediation is an emerging approach and possess edge over conventional methods to remediate Cd from the environment. The present investigation elucidates the adaptive mechanism of a freshwater microalga, Scenedesmus sp. IITRIND2 under Cd stress. The microalga showed excellent tolerance to Cd stress with IC₅₀ value of ~32 ppm. The microalga showed phenomenal removal efficiency (~80%) when exposed to 25 ppm of Cd. Such a high uptake of Cd by the cells was accompanied with increased total lipid content (~33% of dry cell weight). Additionally, the elevated level of ROS, lipid peroxidation, glycine-betaine, and antioxidant enzymes evidenced the activation of efficient antioxidant machinery for alleviating the Cd stress. Further, analysis of the fatty acid methyl ester (FAME) presented a steady increase in saturated and polyunsaturated fatty acids with biodiesel properties complying the American and European fuel standards. The study proposes an integrated approach for bioremediation of toxic Cd using hyper-tolerant microalgal strains along with biodiesel production from the generated algal biomass.