Effects of perfluorooctanoic acid on Microcystis aeruginosa: Stress and self-adaptation mechanisms

Antioxidant system alterations and oxidative stress caused by polyfluoroalkyl substances (PFAS) in exposed biota: a review

Contamination of aquatic and terrestrial organisms by Perfluoroalkyl substances (PFAS), emerging contaminants, is widespread, as these compounds are present in water, soil, air, and food, owing to their environmental persistence. PFAS exposure induces biochemical process alterations associated with the disruption of the antioxidant defense system in several species. This review aims to discuss how PFAS-induced antioxidant system alterations lead to changes in biochemical processes in different organisms exposed to these pollutants. This disruption, then leads to an imbalance in antioxidant defense systems, contributing to the formation of reactive oxidative species (ROS), which, in turn, can be exacerbate oxidative stress, induce cellular damage, enhance lipid peroxidation, destabilize lysosomal membranes, and cause genotoxic effects, ultimately compromising DNA integrity. In acute tests, PFAS have led to mortality, growth inhibition, diminished behavioral and locomotor abilities, and reproductive impairment. PFAS-induced effects differ with varying species or types of substances, and further bioaccumulation through food chains exacerbates environmental contamination, carrying considerable risks. These findings demonstrate the complex and enduring impact of PFAS on environmental health, emphasizing the importance of this review in corroborating studies on sub-lethal toxicity in exposed organisms and how these effects reflect on the environment.

Mechanisms of PFBA toxicity in Chlorella vulgaris: Photosynthesis, oxidative stress, and antioxidant impairment

Perfluorobutanoic acid (PFBA), an emerging alternative to perfluorooctanoic acid (PFOA), has become increasingly prevalent in aquatic ecosystems, yet its ecotoxicological impacts remain poorly understood. This study investigated the aquatic toxicity of PFBA using the freshwater algae Chlorella vulgaris (C. vulgaris) as a model organism, employing a 96h pre-exposure assay to determine the median effective concentration followed by acute toxicity experiments analyzing multiple endpoints including growth, photosynthetic parameters, oxidative stress markers, and antioxidant enzyme activities. Computer simulation techniques were utilized to illustrate the underlying molecular mechanisms of PFBA toxicity. The results showed that the 96h-EC50 value of PFBA was 154.88 mg/L, which is comparable to conventional per- and polyfluoroalkyl substances (PFAS). Acute toxicity experiments revealed a biphasic dose-response relationship to the algal growth with the hormetic effects at the lower concentrations (30.97-92.93 mg/L) but inhibition at the higher levels (123.91-185.86 mg/L) of PFBA. High dosages of PFBA significantly decreased the maximum photosynthetic yield (Fv/Fm) and relative electron transfer rate (rETR), while inducing oxidative stress and inhibiting superoxide dismutase (SOD) and catalase (CAT) activities. Future AlphaFold2 modeling and molecular docking simulations demonstrated the potential binding of PFBA to photosystem II D1 C-terminal processing protease (PSII D1 protein), SOD, and CAT. These findings reveal a complex toxicity mechanism of PFBA on C. vulgaris involving photosynthetic disruption, oxidative stress, and antioxidant system impairment, contributing to the understanding of short-chain PFAS alternative ecotoxicity in aquatic ecosystems.

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.

Stimulation of Microcystis aeruginosa by subtoxic concentrations of contaminants: A meta-analysis

There is growing evidence for hormetic stimulation of Microcystis aeruginosa, a harmful algal bloom (HAB)-forming cyanobacterium, by subtoxic contaminant concentrations. Hence, the first meta-analysis of approximately 4000 dose responses was conducted to evaluate the underlying biological mechanisms, identify variation determinants, and reveal potential implications for algaecides effectiveness. Approximately 30 chemical contaminants caused significant stimulation (95% CI: 72-153%), which persisted in mixtures, regardless the level of mixture complexity. Stimulation by subtoxic antibiotic contamination occurred in the presence or absence of algaecides, highlighting the potential of chemical contamination to lower algaecide efficiency to control the cyanobacterium. The significant stimulation spanned a wide range of contaminant concentrations, from ≤0.0001 to 200 mg L-1, and the response amplitude varied with concentration and exposure duration, increasing from 16% in less than one day to 27% on average within 2-4 weeks. Various mechanisms regulating the defense system (39-46%) and photosynthetic physiology (10-12%) and determining productivity and yields (19-22%) were enhanced, ultimately resulting in increased population growth (cell density; 21%), growth rate (15%), and survival (39%). Importantly, intracellular and extracellular microcystins (MC-LR, MC-LW, MC-RR, MC-YR) and their release are enriched by 26-29% in tandem with mcyB over-expression (24%) and N (26%) and Ca (17%) enhancement. However, the stimulation degree depended on the specific MC. The findings not only close a significant gap in the scientific understanding of the underlying mechanisms of contaminant-induced stimulation but also provide critical information to improve HAB management and remediation strategies.

Molecular disruptions in microalgae caused by Acidithiobacillus ferrooxidans: Photosynthesis, oxidative stress, and energy metabolism in acid mine drainage

Microalgae are recognized for their potential in the bioremediation of acid mine drainage (AMD), despite the challenges posed by AMD's low pH, high heavy metal content, and oligotrophic conditions. However, the impact of AMD chemoautotrophic microorganisms on microalgal growth and remediation efforts within AMD has been largely overlooked. This study aims to elucidate the effects the chemoautotrophic microorganism, Acidithiobacillus ferrooxidans, on the growth activity and metabolism of acid-tolerant microalgae, and to explore the molecular mechanisms of microalgal response. Our findings reveal that the presence of A. ferrooxidans inhibits the growth and alkaline production of Parachlorella sp. MP1, resulting in a 90.86 % reduction in biomass. Physiological, biochemical, and transcriptomic studies, indicate that oxidative stress, photosynthesis, and energy metabolism are the metabolic processes most affected by A. ferrooxidans. Specifically, A. ferrooxidans introduces an increased production of reactive oxygen species (ROS) in Parachlorella sp. MP1, leading to an upregulation of genes and enzymes associated with peroxisome activity and intensifying oxidative stress within the cells. Downregulation of photosynthesis-related genes disrupts the electron transport chain, inhibiting photosynthesis. Furthermore, alterations in the gene expression of pyruvate and acetyl-CoA metabolic pathways result in energetic pathway disruption. These insights contribute to a better understanding of how A. ferrooxidans influence the growth metabolism of acid-tolerant microalgae in AMD environments and inform the optimization of microalgal application strategies in AMD bioremediation engineering.

How heatwaves impact microalgae in the presence of environmentally relevant PFAS concentration: Metabolic shifts and challenges posed

Per- and polyfluoroalkyl substances (PFAS) are widely distributed in the aquatic environment. While increasing studies have investigated the effects of specific PFAS exposure on microalgae, the impact of environmentally relevant PFAS concentrations, particularly during extreme weather events like heatwaves, remains unclear. For Microcystis aeruginosa, a cyanobacteria causing harmful algal blooms, PFAS exposure promoted growth and photosynthesis by accelerating the TCA cycle, intensifying carbon/nitrogen and nucleotide metabolism, and enhancing antioxidant expression. Moreover, although heatwave exposure alone adversely affected algal growth, co-exposure to PFAS and heatwaves paradoxically enhanced algal growth. This co-exposure also enhanced the expression of photosynthetic pigments and metabolites involved in alanine, aspartate and glutamate metabolism, as well as arginine and proline metabolism (compared to PFAS exposure alone). Nevertheless, co-exposure intensified oxidative stress, leading to differential expression of antioxidants, which may consequently affect the synthesis of membrane lipids. In addition, PFAS adsorption and uptake are primarily influenced by the varying strengths of PFAS molecules in binding with proteins and notably boosted by heatwaves. This study highlights the role of diverse PFAS in microalgae blooms and the influence of heatwave events on pollutant responses, providing scientific foundations for aquatic ecosystem protection against climate and pollution challenges.

Enhancing lead tolerance in spirulina using glycine betaine under high CO2 and salinity for sustainable carbon capture

Microalgae-based carbon capture and utilization (CCU) offers a promising negative emission technology that absorbs CO2 and generates valuable biomass. However, heavy metal pollutants in industrial flue gases can compromise carbon sequestration efficiency and bioproduct quality. Spirulina was investigated as a model organism for CO2 sequestration, using a modified Zarrouk's medium to integrate salt stress and an osmoprotectant to boost biomass yield under 15 % CO2. This approach enhances both biomass yield （380.83 mg L-1 d-1）and resistance to lead toxicity. Analytical assessments revealed that glycine betaine (GB) supplementation drastically reduced lead accumulation, decreasing the extracellular and intracellular contents by 39.7 % and 60.7 %, respectively. A notable decrease in extracellular dissolved organic matter was also observed. Furthermore, transcriptomic analyses confirmed that GB treatment strengthened osmotic stress responses and suppressed metal ion transport. These findings enhanced the feasibility of microalgae-based CCU technologies, marking significant progress in sustainable algal biotechnology.

Concentration-dependent cellular responses of coontail (Ceratophyllum demersum) during the substitutions to perfluorooctanoic acid by its two alternatives

The substitutions of alternatives to legacy per- and polyfluoroalkyl substances (PFASs) may lead to unknown and variational joint toxicity on ecosystems. To comprehensively understand the effects of substitutions on aquatic ecosystems, the single and joint effects of perfluorooctanoic acid (PFOA) and its alternatives (perfluorobutanoic acid, PFBA; 2,3,3,3-tetrafluoro-2-(1,1,2,2,3,3,3,heptafluoropropoxy)propanoic acid, GenX) with various concentrations and compositions on a primary producer, coontail (Ceratophyllum demersum), were investigated at cellular level. Results showed that the substitutions of PFBA/GenX could alleviate the inhibition of PFOA on plant length, hydrogen peroxide accumulation, and chlorophyll b, due to the shifts of reactive oxygen species and their less toxicity to antioxidants. Significant up-regulations of superoxide dismutase, glutathione, and carotenoid implied their primary roles in defensing against PFASs (p < 0.05). Catalase/peroxidase was significantly up-regulated in PFBA/GenX substitutions (p < 0.05) to help alleviate stress. PFBA substitutions reduced 23.9 % of PFOA in organelle and GenX reduced the subcellular concentrations of PFOA by 1.8-17.4 %. Redundancy analysis suggested that PFOA, PFBA, and GenX in cell wall and organelle, as well as GenX in soluble fractions, were responsible for the cellular responses. These findings were helpful to understand the integrated effects on aquatic ecosystems during the substitutions to legacy PFASs by alternatives.

Self-aggregation effect of the ternary system "Alga EPS-DOM-HMs" and the characterization of the self-adaptation metabolic response of microalgae

Heavy metals (HMs) present in the natural aquatic environment can form a ternary aggregate of "EPS-DOM-HMs" with the prevalent microalgae extracellular polymers substances (EPS) and macromolecular dissolved organic matters (DOMs), which show special molecular structure and biological interaction. This study reveals the formation of "EPS-TA-HMs" and the mechanism of their physiological and metabolic effects on Raphidocelis subcapitata. Results indicate that TA-Cr(III) can bind to EPS to form ternary aggregates with substances coexisting large and small hydrodynamic diameters and that the interactions are dominated by hydrophobic interactions of the protein binding to the pyrrole ring of the polyphenol and hydrogen bonding interactions formed by OC-(N R O). The protein structure of EPS has the largest proportion of proline, glycine, aspartic acid, and tryptophan. These interactions promoted the secretion of EPS components and reduced the growth inhibition of Raphidocelis subcapitata by 45.9 % compared with Cr(III) exposure. TEM analysis combined with EDS analysis indicated that Cr(III) was taken intracellularly and TA-Cr(III) was not. In addition, metabolomics analyses revealed that microalgae initiate adaptive mechanisms via the activation of a two-component system (i.e., maintenance of high metabolic activity). This study underscored the morphology of HMs in real aquatic environments and the mechanisms of metabolic effects on aquatic organisms.

Response and adaptation of Chlorella pyrenoidosa to 6PPD: Physiological and genetic mechanisms

The extensive contamination of the tire antidegradant N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) in aquatic environments have raised concerns about its potential threats to aquatic organisms. Here, the responses of green algae Chlorella pyrenoidosa (C. pyrenoidosa) to 6PPD exposure were investigated for the first time. The growth of C. pyrenoidosa experienced three sequential phases, including inhibition, recovery and stimulation. Physiological and transcriptome analysis suggested that the growth inhibition was associated with the suppressed nitrogen assimilation and amino acid biosynthesis pathways, among which nitrate transporter (NRT) 2.1 was a key target of 6PPD. Molecular docking revealed the steadily binding of 6PPD to the substrate entry region of NRT 2.1 via hydrogen bonds and π - cation interaction, blocking the acquisition of extracellular inorganic nitrogen. Along with the removal of 6PPD through abiotic processes and biodegradation, an adaptive metabolic shift in cells not only facilitated growth recovery but also triggered a compensatory stimulation phase. With regard to microalgal adaptation, upregulated DNA replication and repair pathways served to maintain the integrity of the genetic information, enhanced photosynthesis cascades and central carbon metabolism improved carbon flux and energy conversion to microalgal biomass, recovered amino acid biosynthesis produced essential proteins for multiple metabolisms. The results provide new insights into microalgal molecular responses to 6PPD exposure, facilitating a better understanding of ecological consequences of 6PPD in the environment.

Perborate Activated Peroxymonosulfate Process for Improving the Coagulation Efficiency of Microcystis aeruginosa by Polymeric Aluminum Chloride

In this study, the sodium perborate (SP)-activated peroxymonosulfate (PMS) process was used to enhance the coagulation efficiency of cyanobacteria with polymeric aluminum chloride (PAC), aiming to efficiently mitigate the impact of algal blooms on the safety of drinking water production. The optimal concentrations of SP, PMS, and PAC were determined by evaluating the removal rate of OD680 and zeta potential of the algae. Experimental results demonstrated that the proposed ternary PMS/SP/PAC process achieved a remarkable OD680 removal efficiency of 95.2%, significantly surpassing those obtained from individual treatments with PMS (19.5%), SP (5.2%), and PAC (42.1%), as well as combined treatments with PMS/PAC (55.7%) and PMS/SP (28%). The synergistic effect of PMS/SP/PAC led to the enhanced aggregation of cyanobacteria cells due to a substantial reduction in their zeta potential. Flow cytometry was performed to investigate cell integrity before and after treatment with PMS/SP/PAC. Disinfection by-products (DBPs) (sodium hypochlorite disinfection) of the algae-laden water subsequent to PMS/SP/PAC treatment declined by 57.1%. Moreover, microcystin-LR was completely degraded by PMS/SP/PAC. Electron paramagnetic resonance (EPR) analysis evidenced the continuous production of SO4•-, •OH, 1O2, and O2•-, contributing to both cell destruction and organic matter degradation. This study highlighted the significant potential offered by the PMS/SP/PAC process for treating algae-laden water.

Physiological and transcriptome level responses of Microcystis aeruginosa and M. viridis to environmental concentrations of triclosan

The toxicity of triclosan (TCS) to various aquatic organisms has been demonstrated at environmental concentrations. However, the effects and mechanisms of TCS on toxic cyanobacteria remains largely unexplored. This study investigated the physiological and molecular variations in two representative toxic Microcystis species (M. aeruginosa and M. viridis) under exposure to TCS for 12 d. Our findings demonstrated that the median effective concentration (EC50) of TCS for both Microcystis species were close to the levels detected in the environment (M. aeruginosa: 9.62 μg L-1; M. viridis: 27.56 μg L-1). An increased level of reactive oxygen species (ROS) was observed in Microcystis, resulting in oxidative damage when exposed to TCS at concentrations ranging from 10 μg L-1 to 50 μg L-1. The photosynthetic activity of Microcystis had a certain degree of recovery capability at low concentrations of TCS. Compared to M. aeruginosa, the higher recovery capability of the photosynthetic system in M. viridis would be mainly attributed to the increased ability for PSII repair and phycobilisome synthesis. Additionally, the synthesis of microcystins in the two species and the release rate in M. viridis significantly increased under 10-50 μg L-1 TCS. At the molecular level, exposure to TCS at EC50 for 12 d induced the dysregulation of genes associated with photosynthesis and antioxidant system. The upregulation of genes associated with microcystin synthesis and nitrogen metabolism further increased the potential risk of microcystin release. Our results revealed the aquatic toxicity and secondary ecological risks of TCS at environmental concentrations, and provided theoretical data with practical reference value for TCS monitoring.

Unraveling the toxicity response and metabolic compensation mechanism of tannic acid-Cr(III) complex on alga Raphidocelis subcapitata

Due to their assembly properties and variable molecular weights, the potential biological toxicity effects of macromolecular organic ligand heavy metal complexes are more difficult to predict and their mechanisms are more complex. This study unraveled the toxicity response and metabolic compensation mechanism of tannic acid-Cr(III) (TA-Cr(III)) complex on alga Raphidocelis subcapitata using multi-omics approaches. Results showed TA-Cr(III) complex caused oxidative damage and photosystem disruption, destroying the cell morphology and inhibiting algal growth by >80 % at high exposure levels. TA-Cr(III) complex stress down-regulated proteins linked to proliferation, photosynthesis and antioxidation while upregulating carbon fixation, TCA cycle and amino acid metabolism. The increase of fumarate, citrate, isocitrate and semialdehyde succinate was validated by metabolomics analysis, which improved the TCA cycle, amino acid metabolism and carbon fixation. Activation of the above cellular processes somewhat compensated for the inhibition of algal photosynthesis by TA-Cr(III) complex exposure. In conclusion, physiological toxicity coupled with downstream metabolic compensation in response to Cr(III) complex of macromolecular was characterized in Raphidocelis subcapitata, unveiling the adaptive mechanism of algae under the stress of heavy metal complexes with macromolecular organic ligands.

Effects of sulfamonomethoxine and trimethoprim co-exposures at different environmentally relevant concentrations on microalgal growth and nutrient assimilation

In aquaculture around the world, sulfamonomethoxine (SMM), a long-acting antibiotic that harms microalgae, is widely employed in combination with trimethoprim (TMP), a synergist. However, their combined toxicity to microalgae under long-term exposures at environmentally relevant concentrations remains poorly understood. Therefore, we studied the effects of SMM single-exposures and co-exposures (SMM:TMP=5:1) at concentrations of 5 μg/L and 500 μg/L on Chlorella pyrenoidosa within one aquacultural drainage cycle (15 days). Photosynthetic activity and N assimilating enzyme activities were employed to evaluate microalgal nutrient assimilation. Oxidative stress and flow cytometry analysis for microalgal proliferation and death jointly revealed mechanisms of inhibition and subsequent self-adaptation. Results showed that exposures at 5 μg/L significantly inhibited microalgal nutrient assimilation and induced oxidative stress on day 7, with a recovery to levels comparable to the control by day 15. This self-adaptation and over 95 % removal of antibiotics jointly contributed to promoting microalgal growth and proliferation while reducing membrane-damaged cells. Under 500 μg/L SMM single-exposure, microalgae self-adapted to interferences on nutrient assimilation, maintaining unaffected growth and proliferation. However, over 60 % of SMM remained, leading to sustained oxidative stress and apoptosis. Remarkably, under 500 μg/L SMM-TMP co-exposure, the synergistic toxicity of SMM and TMP significantly impaired microalgal nutrient assimilation, reducing the degradation efficiency of SMM to about 20 %. Consequently, microalgal growth and proliferation were markedly inhibited, with rates of 9.15 % and 17.7 %, respectively, and a 1.36-fold increase in the proportion of cells with damaged membranes was observed. Sustained and severe oxidative stress was identified as the primary cause of these adverse effects. These findings shed light on the potential impacts of antibiotic mixtures at environmental concentrations on microalgae, facilitating responsible evaluation of the ecological risks of antibiotics in aquaculture ponds.

Polystyrene microplastics enhanced the effect of PFOA on Chlorella sorokiniana: Perspective from the cellular and molecular levels

Microplastics (MPs) commonly coexist with other contaminants and alter their toxicity. Perfluorooctanoic acid (PFOA), an emerging pollutant, may interact with MPs but remain largely unknown about the joint toxicity of PFOA and MPs. Hence, this research explored the single and joint effects of PFOA and polystyrene microplastics (PS-MPs) on microalgae (Chlorella sorokiniana) at the cellular and molecular levels. Results demonstrated that PS-MPs increased PFOA bioavailability by altering cell membrane permeability, thus aggravating biotoxicity (synergistic effect). Meanwhile, the defense mechanisms (antioxidant system modulation and extracellular polymeric substances secretion) of Chlorella sorokiniana were activated to alleviate toxicity. Additionally, transcriptomic analysis illustrated that co-exposure had more differential expression genes (DEGs; 4379 DEGs) than single-exposure (PFOA: 2533 DEGs; PS-MPs: 492 DEGs), which were mainly distributed in the GO terms associated with the membrane composition and antioxidant system. The molecular regulatory network further revealed that PS-MPs and PFOA primarily regulated the response mechanisms of Chlorella sorokiniana by altering the ribosome biogenesis, photosynthesis, citrate cycle, oxidative stress, and antioxidant system (antioxidant enzyme, glutathione-ascorbate cycle). These findings elucidated that PS-MPs enhanced the effect of PFOA, providing new insights into the influences of MPs and PFOA on algae and the risk assessment of multiple contaminants. ENVIRONMENTAL IMPLICATION: MPs and PFAS, emerging contaminants, are difficult to degrade and pose a non-negligible threat to organisms. Co-pollution of MPs and PFAS is ubiquitous in the aquatic environment, while risks of co-existence to organisms remain unknown. The present study revealed the toxicity and defense mechanisms of microalgae exposure to PS-MPs and PFOA from cellular and molecular levels. According to biochemical and transcriptomic analyses, PS-MPs increased PFOA bioavailability and enhanced the effect of PFOA on Chlorella sorokiniana, showing a synergistic effect. This research provides a basis for assessing the eco-environmental risks of MPs and PFAS.

Repeated Exposure Enhanced Toxicity of Clarithromycin on Microcystis aeruginosa Versus Single Exposure through Photosynthesis, Oxidative Stress, and Energy Metabolism Shift

Antibiotics are being increasingly detected in aquatic environments, and their potential ecological risk is of great concern. However, most antibiotic toxicity studies involve single-exposure experiments. Herein, we studied the effects and mechanisms of repeated versus single clarithromycin (CLA) exposure on Microcystis aeruginosa. The 96 h effective concentration of CLA was 13.37 μg/L upon single exposure but it reduced to 6.90 μg/L upon repeated exposure. Single-exposure CLA inhibited algal photosynthesis by disrupting energy absorption, dissipation and trapping, reaction center activation, and electron transport, thereby inducing oxidative stress and ultrastructural damage. In addition, CLA upregulated glycolysis, pyruvate metabolism, and the tricarboxylic acid cycle. Repeated exposure caused stronger inhibition of algal growth via altering photosynthetic pigments, reaction center subunits biosynthesis, and electron transport, thereby inducing more substantial oxidative damage. Furthermore, repeated exposure reduced carbohydrate utilization by blocking the pentose phosphate pathway, consequently altering the characteristics of extracellular polymeric substances and eventually impairing the defense mechanisms of M. aeruginosa. Risk quotients calculated from repeated exposure were higher than 1, indicating significant ecological risks. This study elucidated the strong influence of repeated antibiotic exposure on algae, providing new insight into antibiotic risk assessment.

Time-course adaption strategy of Tetraselmis-based consortia in response to 17α-ethinylestradiol

Estuarine ecosystem constitutes a microenvironment where the abundant green microalga Tetraselmis sp. co-exists with 17α-ethinylestradiol (EE2) pollution. However, the adaption mechanisms of this microalga-based consortia under EE2 shock are rarely recognized. Using extracellular polymeric substance (EPS) characterization, flow cytometry and transcriptomic, this study reveals the time-course response of Tetraselmis-based consortia under EE2 stress. Compared to the insignificant effect of 0.5 mg/L, a high dose of 2.5 mg/L EE2 induces persistent production of reactive oxygen species (ROS) and transiently physiological damages (membrane, chloroplast, organelle morphogenesis, and DNA replication), resulting in cell cycle alteration and division inhibition. These damages could be recovered through active DNA repair and persistently detoxifying processes of enhanced metabolism and ROS quenching. The enhanced EPS production is observed and in line with the significant up-regulation of most key enzymes involved in precursor synthesis and polysaccharides assembling. However, the up-regulation of glycoside hydrolases and most glycosyltransferases, down-regulation of flippases and changed expression of ABC family members indicate the changed EPS composition and synthesis strategy. The resulting increased colloidal polysaccharide is further consumed by associated bacteria whereas protein remains in the co-cultures. These results provide deeper insights into the adverse effects of chemical compounds to microalgae-bacteria and their coadaptation ability.

Effects of combined exposure of PVC and PFOA on the physiology and biochemistry of Microcystis aeruginosa

Microplastics (MPs) and per- and polyfluoroalkyl substances (PFASs) have drawn significant attention as emerging threats to aquatic ecosystems. There are currently just a few investigations on the combined toxicity of PFAS and MP on freshwater microalgae. In this research, the combined toxicity of polyvinyl chloride (PVC) and perfluorooctanoic acid (PFOA) to Microcystis aeruginosa was investigated. The results indicated that the combination of these pollutants inhibited the growth of M. aeruginosa and promoted the synthesis and release of Microcystin-LR (MC-LR). Individual and combined exposure caused different responses to cellular oxidative stress. Under the Individual exposure of PFOA, when the concentration was greater than 20.0 mg/L, the catalase (CAT) activity increased significantly, and when it was greater than 100.0 mg/L, the malondialdehyde (MDA) content increased significantly, but there is no significant change under combined exposure. PVC and PFOA exposure also caused physical damage to the algal cells and reduced the content of extracellular polymer substances (EPS) based on analysis of cell morphology. Metabolic analysis revealed that carbohydrate metabolism and amino acid metabolism of the algae were affected. The current study offers a fresh theoretical framework for MPs and PFASs environmental risk evaluations.

Photosynthetic response mechanism to polybrominated diphenyl ether exposure in Chlorella pyrenoidosa

Polybrominated diphenyl ether (PBDE) contamination is common in aquatic environments and can severely damage aquatic organisms. However, there is a lack of information on the response and self-adaptation mechanisms of these organisms. Chlorella pyrenoidosa was treated with 2,2',4,4'-tetrabromodiphenyl ether (BDE47), causing significant growth inhibition, pigment reduction, oxidative stress, and chloroplast atrophy. Photosynthetic damage contributed to inhibition, as indicated by Fv/Fm, Chl a fluorescence induction, photosynthetic oxygen evolution activity, and photosystem subunit stoichiometry. Here, Chl a fluorescence induction and quinone electron acceptor (QA-) reoxidation kinetics showed that the PSII donor and acceptor sides were insensitive to BDE47. Quantitative analyses of D1 and PsaD proteins illustrated that PSII and PSI complexes were the main primary targets of photosynthesis inhibition by BDE47. Significant modulation of PSII complex might have been caused by the potential binding of BDE47 on D1 protein, and molecular docking was performed to investigate this. Increased activation of antioxidant defense systems and photosystem repair as a function of exposure time indicated a positive resistance to BDE47. After a 5-day exposure, 23 % of BDE47 was metabolized. Our findings suggest that C. pyrenoidosa has potential as a bioremediator for wastewater-borne PBDEs and can improve our understanding of ecological risks to microalgae.

New insight into the concentration-dependent removal of multiple antibiotics by Chlorella sorokiniana

Microalgae have attracted increasing attention as an environmentally friendly treatment for antibiotics. However, the effect of antibiotic concentration on the removal ability of microalgae with the underlying mechanisms remains unclear. Thus, this work investigates the removal of tetracycline (TET), sulfathiazole (STZ), and ciprofloxacin (CIP) at different concentrations using Chlorella sorokiniana. The results indicate that microalgae have a concentration-dependent effect on antibiotic removal; however, the removal trends for the three antibiotics differed significantly. Specifically, TET showed nearly 100% removal efficiency at any concentration. The high concentration of STZ inhibited microalgal photosynthesis and induced the production of ROS, leading to antioxidant damage and inhibiting removal efficiency. Conversely, CIP enhanced the ability of microalgae to remove CIP by inducing a dual peroxidase and cytochrome p450 enzyme response. Furthermore, the economic analysis demonstrated that microalgae treatment antibiotics were calculated to be 4.93€/m³, which becomes cheaper than the other microalgae water treatment process.

Response mechanisms of Chlorella sorokiniana to microplastics and PFOA stress: Photosynthesis, oxidative stress, extracellular polymeric substances and antioxidant system

Co-pollution of microplastics and per- and polyfluoroalkyl substances (PFAS) is prevailing in the aquatic environment. However, the risks of coexisting microplastics and PFAS on organisms remain unknown. This study investigated the response mechanisms of Chlorella sorokiniana (C. sorokiniana) under polystyrene microplastics (PS-MPs) and perfluorooctanoic acid (PFOA) stress, including toxicity and defense mechanisms. C. sorokiniana was exposed to PS-MPs (10 mg/L) and PFOA (0.05, 0.5, and 5 mg/L) and their mixtures for 96 h, respectively. We found that the dominant toxicity mechanism of PFOA and PS-MPs to C. sorokiniana was dissimilar. PS-MPs mainly inhibited photosynthesis through shading effect, while PFOA mainly induced oxidative stress by reactive oxygen species. The co-exposure of PFOA and PS-MPs aggravated biotoxicity (maximum inhibition rate: 27.27 ± 2.44%), such as photosynthesis inhibition, physical damage, and oxidative stress, compared with individuals. To alleviate toxicity, C. sorokiniana activated defense mechanisms. Extracellular polymeric substances were the first barrier to protect cells, the effect on its secretion was ordered PS-MPs+5PFOA > PS-MPs > 5PFOA, and IBRv2 values were 2.37, 1.35, 1.11, respectively. Antioxidant system was thought of second defense pathway, the influence order of treatment groups was PS-MPs+5PFOA > 5PFOA > PS-MPs, and its IBRv2 values were 2.89, 1.69, 0.25, respectively. Our findings provide valuable information on the complex impacts of PFOA and PS-MPs, which facilitate the ecological risk assessment of multiple pollutants.

Toxicity Effects of Perfluorooctanoic Acid (PFOA) and Perfluorooctane Sulfonate (PFOS) on Two Green Microalgae Species

Amongst per- and polyfluoroalkyl substances (PFAS) compounds, perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) have a high persistence in physicochemical and biological degradation; therefore, the accumulation of PFOS and PFOA can negatively affect aquatic organisms and human health. In this study, two microalgae species (Chlorella vulgaris and Scenedesmus obliquus) were exposed to different concentrations of a PFOS and PFOA mixture (0 to 10 mg L^-1). With increases in the contact time (days) and the PFAS concentration (mg L^-1) from 1 to 7, and 0.5 to 10, respectively, the cell viability, total chlorophyll content, and protein content decreased, and the decrease in these parameters was significantly greater in Scenedesmus obliquus. As another step in the study, the response surface methodology (RSM) was used to optimize the toxicity effects of PFAS on microalgae in a logical way, as demonstrated by the high R² (>0.9). In another stage, a molecular docking study was performed to monitor the interaction of PFOS and PFOA with the microalgae, considering hydrolysis and the enzymes involved in oxidation-reduction reactions using individual enzymes. The analysis was conducted on carboxypeptidase in Chlorella vulgaris and on c-terminal processing protease and oxidized cytochrome c6 in Scenedesmus obliquus. For the enzyme activity, the affinity and dimensions of ligands-binding sites and ligand-binding energy were estimated in each case.