Effect of iron oxide nanoparticles on mixotrophic cultivation of Chlorella spp. for biofuel production.

The current study investigated the effect of iron oxide nanoparticles (IONPs) on mixotrophic microalgae cultivation in wastewater for biofuel production. Optimal IONPs doses of 10 and 20 mg L-1 increased Chlorella pyrenoidosa growth by 16% and lipid accumulation by 53 %, respectively, compared with the control group. Conversely, the protein content declined drastically, while carbohydrates remained relatively unchanged. A maximum of 15% rise in biomass growth was observed for Chlorella sorokiniana IITRF at an IONPs dose of 20 mg L-1, with no significant variation in biochemical composition. Microalgae grown under mixotrophic conditions with IONPs in a biofilm reactor were more suitable for biogas production than biodiesel, increasing biogas and methane content by 38 and 48%, respectively. The findings suggest that low doses of IONPs can enhance microalgal biomass, biogas production and methane content. Further, metabolomics studies are warranted to investigate the interaction between microalgae and nanoparticles to achieve high-quality biodiesel.

Effect of phytohormone on proliferation and accumulation of cellular metabolites of microalgae Isochrysis zhanjiangensis.

Phytohormones play a role in regulating microalgae cells tolerance to adversity. This paper examines the effects of different temperatures (20 °C, 25 °C, 30 °C and 35 °C) on the physiological characteristics and endogenous phytohormones of the Isochrysis Zhanjiangensis (IZ) and its mutagenic strain (3005). The results showed that the endogenous phytohormones indole acetic acid (IAA) and jasmonic acid (JA) exhibited significant differences (P<0.05) between the two strains. The addition of 0.5 mg·L-1 exogenous JA inhibitor ibuprofen (IBU) improved cell growth of IZ, and was extremely effective in the accumulation of polysaccharides, which accounted for 33.25 %. Transcriptomic analyses revealed that genes involved in photosynthesis, such as PetC and PsbO, exhibited significantly elevated expression of the strain IZ, while the pathways related to JA synthesis may be the factor affecting microalgae temperature tolerance. This study provides a theoretical foundation for elucidating the underlying mechanisms and potential applications for high temperature tolerance in IZ.

Phytohormone-induced changes in growth, physiology, and biochemistry of Aurantiochytrium sp. for sustainable bioproduction.

The study aimed to assess the effects of nine combinations of phytohormones, salicylic acid (SA), gibberellic acid (GA), and jasmonic acid (JA) on the growth, physiology, and biochemistry of Aurantiochytrium sp. Parameters like optical density (OD), biomass, protein content, hydrogen peroxide (H2O2), malondialdehyde (MDA), catalase activity (CAT), and gene expression (malic enzyme (ME) and acetyl-CoA carboxylase (ACCase)) were assessed at various cultivation stages (24, 48, 72, and 96 h). The research also analyzed fatty acid composition, unsaturated fatty acids (UFA), saturated fatty acids (SFA), and the UFA to SFA ratio (USS) to understand the biochemical changes induced by phytohormones. Results demonstrated that modifying phytohormone concentrations significantly affected the characteristics of the microalgae, particularly in correlation with different growth stages, emphasizing the necessity of precise control of phytohormone levels for optimizing cultivation conditions and enhancing bioactive compound production in Aurantiochytrium sp.

Amide groups within polystyrene accelerates tetracycline removal in a continuous advanced microalgal treatment system.

Livestock effluents are challenging to be treated owing that antibiotics and microplastics are untargeted for most biological technologies. As far, microalgal wastewater treatment is recognized as an effective technique for dealing with. In this study, a continuous-flow system was conducted over 45 days to evaluate the effectiveness of Chlamydomonas sp. JSC4 in removing tetracycline (TCH) under the influence of polystyrene (PS). It shows that PS significantly enhanced the dissipation efficiency of TCH from livestock effluents, and 9.83 % TCH removal was increased under 5 mg/L of both TCH and PS exposure. Meanwhile, higher microalgal bioactivity was a significant factor in achieving desirable pollutants removal efficiency, as 87.14 % microalgal biomass was improved owing to reduction of oxidative stress and augmentation of photosynthesis. Importantly, the pivotal active sites, NH2 and CO, were rapidly covered via π-π interactions and hydrogen bonds during adsorption process between TCH and PS, accounting for mitigation of TCH-PS complexes toxicity and improvement of microalgal ribosome metabolism. Additionally, co-exposure to TCH and PS resulted in maximum lipids (0.57 g/L) and energy (20.79 kJ/L) production, further encouraging a fantastic vision for the tertiary process of livestock effluents via advanced microalgal treatment.

Dissecting the mechanism of synergistic interactions between Aspergillus fumigatus and the microalgae Synechocystis sp. PCC6803 under Cd(II) exposure: insights from untargeted metabolomics.

Co-culturing fungi and microalgae may effectively remediate wastewater containing Cd and harvest microalgae. Nevertheless, a detailed study of the mechanisms underlying the synergistic interactions between fungi and microalgae under Cd(II) exposure is lacking. In this study, Cd(II) exposure resulted in a significant enhancement of antioxidants, such as glutathione (GSH), malondialdehyde (MDA), hydrogen peroxide (H2O2) and superoxide dismutase (SOD) compared to the control group, suggesting that the cellular antioxidant defense response was activated. Extracellular proteins and extracellular polysaccharides of the symbiotic system were increased by 60.61 % and ,24.29 %, respectively, after Cd(II) exposure for 72 h. The adsorption behavior of Cd(II) was investigated using three-dimensional fluorescence excitation-emission matrix (3D-EEM), fourier transform infrared spectroscopy (FTIR), and scanning electron microscope (SEM). Metabolomics results showed that the TCA cycle provided effective material and energy supply for the symbiotic system to resist the toxicity of Cd(II); Proline, histidine, and glutamine strengthened the synergistic adsorption capacity of the fungus and microalgae. Overall, the theoretical foundation for a deep comprehension of the beneficial interactions between fungi and microalgae under Cd(II) exposure and the role of the fungal-algal symbiotic system in the management of heavy metal pollution is provided by this combined physiological and metabolomic investigation.

Physiological and transcriptomic analysis reveals the toxicological mechanisms of polystyrene micro- and nano-plastics in Chlamydomonas reinhardtii.

With the accumulation of plastic waste in the environment, the toxicity of micro- and nano-plastics (MNPs) to microalgae has attracted increasing attention. However, the underlying toxic mechanisms of MNPs remain to be elucidated. In this study, we synthesized micro- and nano-scale of polystyrene MNPs (PS MNPs) to investigate their toxicity and toxic mechanisms in Chlamydomonas reinhardtii. We found that PS MNPs significantly inhibit the production of photosynthetic pigments and increase soluble protein content. The detailed analysis of results shows that both materials affect photosynthetic efficiency by damaging the donor side, reaction center, and electron transfer of photosystem II. Moreover, compared to PS MPs, PS NPs have a greater negative impact on algal cells. Analyzing the transcriptome of cells suggests that the most sensitive metabolic pathways in response to PS MNPs involve oxidative phosphorylation, biosynthesis of secondary metabolites, and photosynthesis. Especially, genes related to photosynthesis and oxidative phosphorylation showed significant changes in expression after exposure to PS MNPs. This study provided molecular-level insights into the toxic mechanisms of PS MNPs on microalgae.

Physiological responses of the microalga Isochrysis galbana exposed to polystyrene microplastics with different particle sizes.

Due to continuous increase in marine plastic waste, microplastics are ubiquitous in the marine environment. However, there are few studies on the harmful effects caused by microplastics with different particle sizes, and the interaction between particle size and concentration requires further investigation. This study explored the differences in physiological and biochemical responses, photosynthesis and oxidative stress damage of the microalga Isochrysis galbana exposed to three different particle size microplastics. It was found that different particle sizes and concentrations of microplastics resulted in significant differences (p < 0.05) in the growth rate, photosynthesis, and oxidative stress level of I. galbana. With the decrease of the particle size and lowering concentration of microplastics, the growth rate, photosynthesis and oxidative stress levels of I. galbana were reduced. Significant differences in photosynthesis and oxidative stress levels were observed when I. galbana was exposed to smallest particle size and lowest concentration of microplastics. This study provides new insights about whether polystyrene microplastics of different particle sizes and concentrations exhibit complex effects on microalgae, and explores the underlying reasons for such effects. In short, this study predicts the exacerbating adverse effects of microplastic pollution on the primary productivity, with significant implications for marine food webs and ecosystem health.

Comparison of toxic effects and underlying mechanisms of carbon quantum dots and CdSe quantum dots on Chromochloris zofingiensis from the chemical composition perspective.

Quantum dots (QDs) are widely utilized semiconductor nanocrystal materials with both nanotoxicity and composition-related toxicity. To determine the toxicological impacts and underlying mechanisms of QDs with different compositions on microalgae, carbon QDs (CQDs) and CdSe QDs were used in the present study. Results showed that QDs composed of CdSe were more toxic than QDs composed of carbon, which inhibited cell growth, with reductions in chl b content, chlorophyll fluorescence parameters, and increases in lipids and starch (two major storage substances). In addition, CdSe QDs elevated reactive oxygen species (ROS), resulting in oxidative damage, while CQDs had little effect on antioxidants. Comparative transcriptome analysis showed that gene expression was accelerated by CdSe QDs, and there was a compensatory upregulation of porphyrin metabolism, potentially to support chlorophyll synthesis. In addition, an MYB transcription factor was predicted by weighted gene co-expression network analysis (WGCNA) to serve as regulator in nanoparticle toxicity, while glutathione peroxidase (GPX) and dual-specificity tyrosine phosphorylation regulated kinases 2/3/4 (DYRK2/3/4) may be key mediators of the composition-related toxicity of CdSe QDs. This study highlights the critical role of QDs' composition in determining their impacts on aquatic microalgae, providing a theoretical reference for selecting appropriate QDs materials for various industrial applications.

Enhancing aggregation of microalgae on polystyrene microplastics by high light: Processes, drivers, and environmental risk assessment.

Microplastics (MPs) are emerging pollutants, causing potential threats to aquatic ecosystems and serious concern in aggregating with microalgae (critical primary producers). When entering water bodies, MPs are expected to sink below the water surface and disperse into varying water compartments with different light intensities. However, how light influences the aggregation processes of algal cells onto MPs and the associated molecular coupling mechanisms and derivative risks remain poorly understood. Herein, we investigated the aggregation behavior between polystyrene microplastics (mPS, 10 µm) and Chlorella pyrenoidosa under low (LL, 15 µmol·m-2·s-1), normal (NL, 55 µmol·m-2·s-1), and high light (HL, 150 µmol·m-2·s-1) conditions from integrated in vivo and in silico assays. The results indicated that under LL, the mPS particles primarily existed independently, whereas under NL and HL, C. pyrenoidosa tightly bounded to mPS by secreting more protein-rich extracellular polymeric substances. Infrared spectroscopy analysis and density functional theory calculation revealed that the aggregation formation was driven by non-covalent interaction involving van der Waals force and hydrogen bond. These processes subsequently enhanced the deposition and adherence capacity of mPS and relieved its phytotoxicity. Overall, our findings advance the practical and theoretical understanding of the ecological impacts of MPs in complex aquatic environments.

Microplastics with different functional groups modulate cellular and molecular mechanisms of reduced graphene oxide toxicity on the green microalga, Scenedesmus obliquus.

Even though microplastics (MPs) and graphene nanomaterials (GNMs) have demonstrated individual toxicity towards aquatic organisms, the knowledge gap lies in the lack of understanding regarding their combined toxicity. The difference between the combined toxicity of MPs and GNMs, in contrast to their individual toxicities, and furthermore, the elucidation of the mechanism of this combined toxicity are scientific questions that remain to be addressed. In this study, we examined the individual and combined toxicity of three polystyrene microplastics (MPs) with different functional groups-unmodified, carboxyl-modified (COOH-), and amino-modified (NH2-) MPs-in combination with reduced graphene oxide (RGO) on the freshwater microalga Scenedesmus obliquus. More importantly, we explored the cellular and molecular mechanisms responsible for the observed toxicity. The results indicated that the growth inhibition toxicity of RGO, either alone or in combination with the three MPs, against S. obliquus increased gradually with higher particle concentrations. The mitigating effect of MPs-NH2 on RGO-induced toxicity was most significant at a higher concentration, surpassing the effect of unmodified MPs. However, the MPs-COOH did not exhibit a substantial impact on the toxicity of RGO. Unmodified MPs and MPs-COOH aggravated the inhibition effects of RGO on the cell membrane integrity and oxidative stress-related biomarkers. Additionally, MPs-COOH exhibited a stronger inhibition effect on RGO-induced biomarkers compared to unmodified MPs. In contrast, the MPs-NH2 alleviated the inhibition effect of RGO on the biomarkers. Furthermore, the presence of differently functionalized MPs did not significantly affect RGO-induced oxidative stress and photosynthesis-related gene expression in S. obliquus, indicating a limited ability to modulate RGO genotoxicity at the molecular level. These findings can offer a more accurate understanding of the combined risks posed by these micro- and nano-materials and assist in designing more effective mitigation strategies.

Dose-dependent effects of polystyrene nanoplastics on growth, photosynthesis, and astaxanthin synthesis in Haematococcus pluvialis.

Microalgae play an important role in aquatic ecosystems, but the widespread presence of micro- and nano-plastics (MNPs) poses significant threats to them. Haematococcus pluvialis is well-known for its ability to produce the antioxidant astaxanthin when it experiences stress from environmental conditions. Here we examined the effects of polystyrene nanoplastics (PS-NPs) at concentrations of 0.1, 1, and 10 mg/L on H. pluvialis over an 18-day period. Our results show that PS-NPs caused a significant, dose-dependent inhibition of H. pluvialis growth and a reduction in photosynthesis. Furthermore, PS-NPs severely damaged the morphology of H. pluvialis, leading to cell shrinkage, collapse, content release, and aggregation. Additionally, PS-NPs induced a dose-dependent increase in soluble protein content and a decrease in the production of extracellular polymeric substances. These findings indicate that PS-NPs has the potential to adversely affect both the physiology and morphology of H. pluvialis. An increase in reactive oxygen species and antioxidant enzyme activities was also observed, suggesting an oxidative stress response to PS-NPs exposure. Notably, the synthesis of astaxanthin, which is crucial for H. pluvialis's survival under stress, was significantly inhibited in a dose-dependent manner under strong light conditions, along with the down-regulation of genes involved in the astaxanthin biosynthesis pathway. This suggests that PS-NPs exposure reduces H. pluvialis's ability to survive under adverse conditions. This study enhances our understanding of the toxic effects of PS-NPs on microalgae and underscores the urgent need for measures to mitigate MNP pollution to protect aquatic ecosystems.

General performance, kinetic modification, and key regulating factor recognition of microalgae-based sulfonamide removal.

Sulfonamides have been widely detected in water treatment plants. Advanced wastewater treatment for sulfonamide removal based on microalgal cultivation can reduce the ecological risk after discharge, achieve carbon fixation, and simultaneously recover bioresource. However, the general removal performance, key factors and their impacts, degradation kinetics, and potential coupling technologies have not been systematically summarized. To guide the construction and enhance the efficient performance of the purification system, this study summarizes the quantified characteristics of sulfonamide removal based on more than 100 groups of data from the literature. The biodegradation potential of sulfonamides from different subclasses and their toxicity to microalgae were statistically analyzed; therefore, a preferred option for further application was proposed. The mechanisms by which the properties of both sulfonamides and microalgae affect sulfonamide removal were comprehensively summarized. Thereafter, multiple principles for choosing optimal microalgae were proposed from the perspective of engineering applications. Considering the microalgal density and growth status, a modified antibiotic removal kinetic model was proposed with significant physical meaning, thereby resulting in an optimal fit. Based on the mechanism and regulating effect of key factors on sulfonamide removal, sensitive and feasible factors (e.g., water quality regulation, other than initial algal density) and system coupling were screened to guide engineering applications. Finally, we suggested studying the long-term removal performance of antibiotics at environmentally relevant concentrations and toxicity interactions for further research.

Synergistic effect of selenium and gibberellic acid for enhanced biomass, lipid and improved biodiesel quality from Tetradesmus obliquus through response surface methodology.

Biodiesel production from microalgae presents an innovative solution for renewable energy. This study investigates biodiesel production using Tetradesmus obliquus ON506010.1 by optimizing substrates, selenium and gibberellic acid. Using 15 µg/L selenium, lipid content and biomass productivity reached 35.45 %±0.92 and 0.178 g/L/day ± 0.051. With 50 µM gibberellic acid, biomass productivity and lipid content peaked at 0.785 ± 0.101 g/L/day and 38.95 %±0.35, surpassing the control. Fatty acid composition, biodiesel properties, and mRNA expression of lipid synthesis enzymes (acetyl CoA carboxylase (ACC) and fatty acid desaturase (FAD)) correlated. Combining 10 µg/L selenium with 75 µM gibberellic acid with response surface methodology (RSM) increased lipid content (42.80 % ±0.11) and biomass productivity (0.964 g/L/day ± 0.128). ACC and FAD upregulation validated this enhancement, with a 4.4-fold increase in FAD expression. Fatty acid composition and most biodiesel properties met international standards demonstrating Tetradesmus obliquus ON506010.1's potential for sustainable biodiesel production with better cold flow property and oxidative stability.

In situ activation of peroxymonosulfate with bioelectricity for sulfamethoxazole sustainable removal.

Conventional electrochemical activation of peroxymonosulfate (PMS) is not very cost-effective and practical by the excessive input of energy. The electricity generated by photosynthetic microalgae fuel cells (MFCs) is utilized to activate PMS, which would achieve the combination of green bioelectricity and advanced oxidation processes for sustainable pollutants degradation. In this study, a novel dual-chamber of MFCs was constructed by using microalgae as anode electron donor and PMS as cathode electron acceptor, which was operating under both close-circuit and open-circuit conditions. Under close-circuit condition, 1-12 mM PMS in cathode was successfully in situ activated, where 32.00%-99.83% of SMX was removed within 24 h, which was about 1.21-1.78 times of that in the open-circuit of MFCs. Meanwhile, a significant increase in bioelectricity generation in MFCs was observed after the accumulation of microalgae biomass (4.65-5.37 mg/L), which was attributed to the efficient electron separation and transfer. Furthermore, the electrochemical analysis demonstrated that SMX or its products were functioned as electronic shuttles, facilitating the electrochemical reaction and altering the electrical capacitance. The quenching experiments and voltage output results reflected that complex active radical (SO4⋅-, ⋅OH, and 1O2) were involved in SMX removal. Seven degradation products of SMX were detected and S-N bond cleavage was the main degradation pathway. Predicted toxicity values calculated by ECOSAR program showed that all the products were less toxic or nontoxic. Finally, the density functional theory (DFT) calculations revealed that the O and N atoms on SMX were more susceptible to electrophilic reactions, which were more vulnerable to be attacked by reactive species. This study provided new insights into the activation of PMS by bioelectricity for SMX degradation, proposing the mechanisms for PMS activation and degradation sites of SMX.

The impact of polystyrene nanoplastics (PSNPs) on physiological and biochemical parameters of the microalgae Spirulina platensis.

Nanoplastics, as emerging pollutants, have harmful effects on living organisms and the environment, the mechanisms and extent of which remain unclear. Microalgae, as one of the most important biological groups in the food chain and sensitive environmental indicators to various pollutants, are considered a suitable option for investigating the effects of nanoplastics. In this study, the effects of polystyrene nanoplastics on the growth rate, dry weight, chlorophyll a and carotenoid levels, proline, and lipid peroxidation in the Spirulina platensis were examined. Three concentrations of 0.1, 1, and 10 mg L-1 of PSNPs were used alongside a control sample with zero concentration, with four repetitions in one-liter containers for 20 days under optimal temperature and light conditions. Various analyses, including growth rate, dry weight, proline, chlorophyll a and carotenoid levels, and lipid peroxidation, were performed. The results indicated that exposure to PSNP stress led to a significant decrease in growth rate, dry weight, and chlorophyll a and carotenoid levels compared to the control sample. Furthermore, this stress increased the levels of proline and lipid peroxidation in Spirulina platensis. Morphological analysis via microscopy supported these findings, indicating considerable environmental risks associated with PSNPs.

Effects of Cadmium and Nickel Mixtures on Multiple Endpoints of the Microalga Raphidocelis subcapitata.

It is crucial to investigate the effects of mixtures of contaminants on aquatic organisms, because they reflect what occurs in the environment. Cadmium (Cd) and nickel (Ni) are metals that co-occur in aquatic ecosystems, and information is scarce on their joint toxicity to Chlorophyceae using multiple endpoints. We evaluated the effects of isolated and combined Cd and Ni metals on multiple endpoints of the chlorophycean Raphidocelis subcapitata. The results showed that Cd inhibited cell density, increased reactive oxygen species (ROS) production (up to 308% at 0.075 mg L-1 of Cd), chlorophyll a (Chl a) fluorescence (0.050-0.100 mg L-1 of Cd), cell size (0.025-0.100 mg L-1 of Cd), and cell complexity in all concentrations evaluated. Nickel exposure decreased ROS production by up to 25% at 0.25 mg L-1 of Ni and Chl a fluorescence in all concentrations assessed. Cell density and oxygen-evolving complex (initial fluorescence/variable fluorescence [F0/Fv]) were only affected at 0.5 mg L-1 of Ni. In terms of algal growth, mixture toxicity showed antagonism at low doses and synergism at high doses, with a dose level change greater than the median inhibitory concentration. The independent action model and dose-level-dependent deviation best fit our data. Cadmium and Ni mixtures resulted in a significant increase in cell size and cell complexity, as well as changes in ROS production and Chl a fluorescence, and they did not affect the photosynthetic parameters. Environ Toxicol Chem 2024;43:1855-1869. © 2024 SETAC.

Oxidative stress and metabolic process responses of Chlorella pyrenoidosa to nanoplastic exposure: Insights from integrated analysis of transcriptomics and metabolomics.

Oxidative stress is a universal interpretation for the toxicity mechanism of nanoplastics to microalgae. However, there is a lack of deeper insight into the regulation mechanism in microalgae response to oxidative stress, thus affecting the prevention and control for nanoplastics hazard. The integrated analysis of transcriptomics and metabolomics was employed to investigate the mechanism for the oxidative stress response of Chlorella pyrenoidosa to nanoplastics and subsequently lock the according core pathways and driver genes induced. Results indicated that the linoleic acid metabolism, glycine (Gly)-serine (Ser)-threonine (Thr) metabolism, and arginine and proline metabolism pathways of C. pyrenoidosa were collectively involved in oxidative stress. The analysis of linoleic acid metabolism suggested that nanoplastics prompted algal cells to secrete more allelochemicals, thereby leading to destroy the immune system of cells. Gly-Ser-Thr metabolism and arginine and proline metabolism pathways were core pathways involved in algal regulation of cell membrane function and antioxidant system. Key genes, such as LOX2.3, SHM1, TRPA1, and proC1, are drivers of regulating the oxidative stress of algae cells. This investigation lays the foundation for future applications of gene editing technology to limit the hazards of nanoplastics on aquatic organism.

Evidence that microplastics at environmentally relevant concentration and size interfere with energy metabolism of microalgal community.

To address two current issues in evaluating the toxicity of microplastics (MPs) namely, conflicting results due to species specificity and the ecological irrelevance of laboratory data, this study conducted a 10-day exposure experiment using a microalgal community comprising three symbiotic species. The experiment involved virgin and Benzo[a]pyrene-spiked micron-scale fibers and fragments made of polyethylene terephthalate (PET) and polypropylene (PP). The results showed that, from a physiological perspective, environmentally relevant concentrations of micron-scale MPs decreased saccharide accumulation in microalgal cells, as confirmed by ultrastructural observations. MPs may increase cellular energy consumption by obstructing cellular motility, interfering with nutrient uptake, and causing sustained oxidative stress. Additionally, MPs and adsorbed B[a]P induced DNA damage in microalgae, potentially further disrupting cellular energy metabolism. Ecologically, MPs altered the species abundance in microalgal communities, suggesting they could weaken the ecological functions of these communities as producers and affect ecosystem diversity and stability. This study marks a significant advancement from traditional single-species toxicity experiments to community-level assessments, providing essential insights for ecological risk assessment of microplastics and guiding future mechanistic studies utilizing multi-omics analysis.

Investigating flocculation mechanisms and ecological safety of cationic guar gum for rapid harvesting of microalgal cells.

Addressing the drawbacks of traditional flocculants on microalgae biomass harvesting is crucial for large-scale industrial applications of microalgae production. In this study, cationic bioflocculant was successfully prepared by introducing cationic groups into the side chain of guar gum, achieving in-situ algae flocculation efficiency of 83.5 % with the dosage of 18.0 mg/L under pH = 10.0. Through a harmonious integration of predictive modelling and practical experimentation, a superior cell flocculation capacity of 23.5 g/g was achieved. In addition, the environmental safety and biocompatibility of cationic guar gum was assessed, using the typical suspension quantitative bacteriostatic method and the fluorescent double-staining technique. The results showed that the inhibition efficiency of Staphylococcus aureus in the system containing 60.0 mg/L cationic guar gum was only 12.0 % and there was no inhibition against Escherichia coli colonies. These findings provide a safe and green flocculant for efficient microalgae harvesting and spent medium treatment.

Multi-faceted effects of NaCl on salt-tolerant microalgae Golenkinia sp. SDEC-16.

The salt-tolerant microalgae are extremely few and salt-tolerance mechanism is unclear, requiring urgent exploration of salt-tolerance mechanism of known microalgae. This study was first to reveal the salt-tolerance mechanism of Golenkinia sp. SDEC-16 by investigating the growth and metabolism under different salinities and high salinity long-term cultivation. SDEC-16 can survive under high salinity and resume normal growth after NaCl removal. Under long-term stress, SDEC-16 had higher lipid content and productivity than BG11. However, the suppressed Fv/Fm (58.4%) and Fv/F0 (84.0%) along with the increased reactive oxygen species (×6.6), and superoxide dismutase (×1.7) during the treatment revealed NaCl-induced photosynthetic inhibition and oxidative stress. RNA sequencing results showed inhibition of the photosynthetic system, and the enhancement of pathways such as nitrogen metabolism, energy metabolism, and lipid synthesis contributed to the good function of chloroplast, energy supply, and metabolic activity of SDEC-16. This study provides theoretical support for large-scale microalgal cultivation in seawater.