Transcriptome analysis of the effect of bisphenol A exposure on the growth, photosynthetic activity and risk of microcystin-LR release by Microcystis aeruginosa

Growth and reproductive toxicity of bisphenol A in Oikopleura dioica at environmentally relevant concentrations

Bisphenol A (BPA), a known endocrine disruptor, is ubiquitous in various aquatic environments. Appendicularians are among the most abundant mesozooplankton populations and occupy a crucial niche in marine ecosystems. However, no toxicological data are available concerning the effects of BPA on this functional group. In this study, an evaluation of the toxicity of environmentally relevant levels of BPA (2.5-150 μg/L) on the appendicularian Oikopleura dioica, including its morphology and transcriptome, was conducted. Our results demonstrated the high sensitivity of O. dioica to BPA, with a LC50 of 142 μg/L. Exposure to 125 μg/L BPA significantly inhibited the somatic growth, gonadal development and reproduction of individuals, whereas exposure to an environmentally safe concentration (2.5 μg/L) affected female fecundity and fitness as well as male gene expression. The results of the transcriptomic analysis suggest that males were more sensitive to BPA stress at the molecular level. BPA exposure not only led to abnormal secretion of digestive enzymes and phospholipase A2, affecting the function of the digestive system and arachidonic acid but also significantly down-regulated the expression of mRNAs related to enzymes involved in carbohydrate and energy metabolism in males. These findings suggest that the current safe environmental concentrations may not be safe.

Impact of butylparaben on growth dynamics and microcystin-LR production in Microcystis aeruginosa

The presence of butylparaben (BP), a prevalent pharmaceutical and personal care product, in surface waters has raised concerns regarding its impact on aquatic ecosystems. Despite its frequent detection, the toxicity of BP to the cyanobacterium Microcystis aeruginosa remains poorly understood. This study investigates the influence of BP on the growth and physiological responses of M. aeruginosa. Results indicate that low concentrations of BP (below 2.5 mg/L) have negligible effects on M. aeruginosa growth, whereas higher concentrations (5 mg/L and 10 mg/L) lead to significant growth inhibition. This inhibition is attributed to the severe disruption of photosynthesis, evidenced by decreased Fv/Fm values and chlorophyll a content. BP exposure also triggers the production of reactive oxygen species (ROS), resulting in elevated activity of antioxidant enzymes. Excessive ROS generation stimulates the production of microcystin-LR (MC-LR). Furthermore, lipid peroxidation and cell membrane damage indicate that high BP concentrations cause cell membrane rupture, facilitating the release of MC-LR into the environment. Transcriptome analysis reveals that BP disrupts energy metabolic processes, particularly affecting genes associated with photosynthesis, carbon fixation, electron transport, glycolysis, and the tricarboxylic acid cycle. These findings underscore the profound physiological impact of BP on M. aeruginosa and highlight its role in stimulating the production and release of MC-LR, thereby amplifying environmental risks in aquatic systems.

Simultaneous inactivation of Microcystis aeruginosa and degradation of microcystin-LR in water by activation of periodate with sunlight

Harmful algal blooms pose tremendous threats to ecological safety and human health. In this study, simulated solar light (SSL) irradiation was used to activate periodate (PI) for the inactivation of Microcystis aeruginosa and degradation of microcystin-LR (MC-LR). We found that PI-SSL system could effectively inactivate 5 × 106 cells·mL-1 algal cells below the limit of detection within 180 min. ·OH and iodine (IO3· and IO4·) radicals generated in PI-SSL system could rupture cell membranes, releasing intracellular substances including MC-LR into the reaction system. However, the released MC-LR could be degraded into non-toxic small molecules via hydroxylation and ring cleavage processes in PI-SSL system, reducing their environmental risks. High algae inactivation performance of PI-SSL system in solution with a wide pH range (3-9), with the coexisting anions (Cl-, NO3- and SO42-) and the copresence of natural organic matters (humic acid and fulvic acid), real water (lake water and river water), as well as in continuous-flow reactor (14 h) were also achieved. In addition, under natural sunlight irradiation, effective algae inactivation could also be achieved in an enlarged reactor (1 L). Overall, our study showed that PI-SSL system could avoid the inference by the background substances and could be employed as a feasible technique to treat algal bloom water.

Effect of surfactant's charge properties on behavior, physiology, and biochemistry and the release of microcystins of Microcystis aeruginosa

Surfactant pollution is escalatitheng in eutrophic waters, but the effect of surfactant charge properties on the physiological and biochemical properties of toxin-producing microalgae remains inadequately explored. To address this gap, this study explores the effects and mechanisms of three common surfactants-cetyltrimethylammonium bromide (CTAB, cationic), sodium dodecyl sulfate (SDS, anionic), and Triton X-100 (nonionic)-found in surface waters, on the agglomeration behavior, physiological indicators, and Microcystin-LR (MC-LR) release of Microcystis aeruginosa (M. aeruginosa) by using UV-visible spectroscope, Malvern Zetasizer, fluorescence spectrometer, etc. Results suggest that charge properties significantly affect cyanobacterial aggregation and cellular metabolism. The CTAB-treated group demonstrates a ∼5.74 and ∼9.74 times higher aggregation effect compared to Triton X-100 and SDS (300 mg/L for 180 min) due to strong electrostatic attraction. Triton X-100 outperforms CTAB and SDS in polysaccharide extraction, attributed to its higher water solubility and lower critical micelle concentration. CTAB stimulates cyanobacteria to secrete proteins, xanthohumic acid, and humic acids to maintain normal physiological cells. Additionally, the results of SEM and ion content showed that CTAB damages the cell membrane, resulting in a ∼90% increase in the release of intracellular MC-LR without cell disintegration. Ionic analyses confirm that all three surfactants alter cell membrane permeability and disrupt ionic metabolic pathways in microalgae. This study highlights the relationship between the surface charge properties of typical surfactants and the dispersion/agglomeration behavior of cyanobacteria. It provides insights into the impact mechanism of exogenous surfactants on toxic algae production in eutrophic water bodies, offering theoretical references for managing surfactant pollution and treating algae blooms.

Physiological and transcriptomic analyses provide preliminary insights into the autotoxicity of Lilium brownii

Lilium brownii F. E. Brown ex Miellez var. viridulum Baker (Longya lily) is a variety of Lilium brownii F.E. Br. ex Miellez. We used HS-SPME and GC-MS to screened the tissues of L. brownii roots, stems, bulbs, and leaves and obtained 2,4-DTBP as an autotoxic substance for subsequent analysis. 2,4-DTBP was highly autotoxic in some treatment groups. Based on changes in physiological indicators, we carried out transcriptomic analysis to investigate the mechanisms of autotoxicity of substances on L. brownii and obtained 188,505 Unigenes. GO and KEGG enrichment analyses showed that L. brownii responded differently to different concentrations and treatment times of 2,4-DTBP. We observed significant changes in genes associated with ROS, phytohormones, and MAPK signaling cascades. 2,4-DTBP affects chloroplasts, the integrity of the respiratory electron transport chain, and ribosomes, causing L. brownii autotoxicity. Our findings provide a practical genomic resource for future research on L. brownii autotoxicity and evidence for the mechanism of action of autotoxic substances.

Biological activity and molecular mechanism of inactivation of Microcystis aeruginosa by ultrasound irradiation

Harmful algal blooms (HABs) significantly impact on water quality and ecological balance. Ultrasound irradiation has proven to be an effective method for algal control. Nevertheless, the molecular mechanisms underlying the inactivation of M. aeruginosa by ultrasound are still unknown. In this study, the physiological activity and molecular mechanism of algal cells exposed to different frequencies of ultrasound were studied. The results indicated a pronounced inhibition of algal cell growth by high-frequency, high-dose ultrasound. Moreover, with increasing ultrasound dosage, there was a higher percentage of algal cell membrane ruptures. SEM and TEM observed obvious disruptions in membrane structure and internal matrix. Hydroxyl radicals generated by high-frequency ultrasound inflicted substantial cell membrane damage, while increased antioxidant enzyme activities fortified cells against oxidative stress. Following 2 min of ultrasound irradiation at 740 kHz, significant differential gene expression occurred in various aspects, including energy metabolism, carbohydrate metabolism, and environmental information processing pathways. Moreover, ultrasound irradiation influenced DNA repair and cellular apoptosis, suggesting that the algal cells underwent biological stress to counteract the damage caused by ultrasound. These findings reveal that ultrasound irradiation inactivates algae by destroying their cell structures and metabolic pathways, thereby achieving the purpose of algal suppression.

The Conversion and Degradation of Sulphaguanidine under UV and Electron Beam Irradiation Using Fluorescence

The work presents a spectral-luminescent study of the sulfaguanidine transformation in water under a pulsed e-beam and UV irradiation of an UVb-04 bactericidal mercury lamp (from 180 to 275 nm), KrCl (222 nm), XeBr (282 nm) and XeCl (308 nm) excilamps. Fluorescent decay curves have been used in our analysis of the sulfaguanidine decomposition. The conversion of antibiotic under e-beam irradiation for up to 1 min was more than 80%, compared with UV radiation: UVb-04-26%, XeBr - 20%. KrCl and XeCl - about 10%. At the end of 64 min of irradiation with UVb-04 and XeBr lamps, the conversion was 99%. During irradiation with these lamps, sulfaguanidine almost completely decomposed and passed into the final fluorescent photoproducts. After e-beam irradiated at the end of 13 min the decrease in sulfaguanidine was 93%. At the same time, the formation of sulfaguanidine transformation products was minimal compared to UV irradiation. The effect of UV irradiation and a powerful e-beam on the decomposition mechanisms of sulfaguanidine are significantly different, which is manifested in various changes in the absorption and fluorescence spectra.

Effective photocatalytic inactivation of Microcystis aeruginosa by Ag3VO4/BiVO4 heterojunction under visible light

In recent years, photocatalytic technology has been increasingly used for the treatment of algal blooms in water bodies due to its high efficiency and environmental advantages. However, conventional semiconductor materials suffer from high electron-hole recombination rate, low carrier mobility and weak surface adsorption ability, which made their photocatalytic performance limited. Therefore, the photocatalytic performance of the composites can be improved by coupling another semiconductor material to form a heterojunction to accelerate electron transfer. In this study, a novel composite Ag3VO4/BiVO4 (ABV) photocatalyst was successfully prepared by in-situ deposition method for the photocatalytic inactivation of Microcystis aeruginosa (M. aeruginosa) under visible light. The photocatalyst showed excellent photocatalytic activity, and the degradation rate of M. aeruginosa chlorophyll a was up to 99.8% within 4 h under visible light. During the photocatalytic degradation, the morphology of algae cells, the permeability of cell membrane, the organic matter inside and outside the cells, the antioxidant system and the soluble protein were seriously damaged. Moreover, three cycle experiments showed that the prepared ABV photocatalyst had high reusability. Finally, a possible mechanism of M. aeruginosa inactivation was proposed. In general, the synthesized ABV photocatalyst can effectively inactivate cyanobacteria under visible light and provided a new method for M. aeruginosa removal in water.

Effects of polystyrene nanoplastics on growth and hemolysin production of microalgae Karlodinium veneficum

There are few studies on the effects of nanoplastics on growth and hemolysin production of harmful algal bloom species at present. In this study, Karlodinium veneficum was exposed to different concentrations (0, 5, 25, 50, 75 mg/L) of polystyrene nanoplastics (PS-NPs, 100 nm) for 96 h. The effects of PS-NPs on growth of K. veneficum were investigated by measuring algal cell abundance, growth inhibition rate (IR), total protein (TP), malondialdehyde (MDA), glutathione reductase (GSH), superoxide dismutase (SOD), ATPase activity (Na+/K+ ATPase and Ca2+/Mg2+ ATPase). Scanning electron microscope and transmission electron microscope (SEM and TEM) images of microalgae with or without nanoplastics were also observed. The effects of PS-NPs on hemolysin production of K. veneficum were studied by measuring the changes of hemolytic toxin production of K. veneficum exposed to PS-NPs on 1, 3, 5 and 7 days. High concentrations (50 and 75 mg/L) of PS-NPs seriously affected the growth of K. veneficum and different degrees of damage to cell morphology and ultrastructure were found. Excessive free radicals and other oxidants were produced in the cells, which disrupted the intracellular redox balance state and caused oxidative damage to the cells, and the basic activities such as photosynthesis and energy metabolism were weakened. The athletic ability of K. veneficum was decreased, but the ability to produce hemolysin was enhanced. It was suggested that the presence of nanoplastics in seawater may strengthen the threat of harmful algal bloom species to aquatic ecosystems and human health.

ROS meditated paralytic shellfish toxins production changes of Alexandrium tamarense caused by microplastic particles

A variety of studies have investigated the toxic effects of microplastics (MPs) on microalgae, but few of them considered their influence on dinoflagellate toxins production, which could cause significant ecological safety concerns in coastal areas. This research investigated the impacts of 5 μg L-1 and 5 mg L-1 polystyrene (PS) MPs on the changes of paralytic shellfish toxins (PSTs) production and their relationship with cellular oxidative stress of Alexandrium tamarense, a common harmful algal blooms causative dinoflagellate. The results showed elevation of reactive oxygen species (ROS) levels, activation of antioxidant system and overproduction of PSTs were positively correlated under PS MPs exposure (especially under 5 mg L-1 PS MPs), and the PSTs changes were eliminated by the ROS inhibitor. Further transcriptomic analysis revealed that ROS could enhance biosynthesis of glutamate, providing raw materials for PSTs precursor arginine, accompanied with enhanced acetyl-CoA and ATP production, finally leading to the overproduction of PSTs. Moreover, the oxidative intracellular environments might block the reduction process from STX to C1&C2, leading to the increase of STX and decrease of C1&C2 proportions. This work brings the first evidence that ROS could mediate PSTs production and compositions of Alexandrium under MPs exposure, with important scientific and ecological significance.

Down-regulation of iron/zinc ion transport and toxin synthesis in Microcystis aeruginosa exposed to 5,4'-dihydroxyflavone

Flavonoids, common natural polyphenolic compounds from plants, have been proposed as highly effective and safe algicides. However, the molecular mechanism of flavonoids inhibiting Microcystis aeruginosa remains unclear. This study aims in exploring the global transcriptional changes and molecular docking in cyanobacterial cells in response to flavonoids. Transcriptomic analysis revealed that 5,4'-dihydroxyflavone (DHF) primarily affected the genes transcription of iron and zinc ion transport, resulting in the blockage of transport for iron (II), iron (III) and zinc (II), which eventually led to a decrease in intracellular iron and zinc content. 5,4'-DHF can also interfere with iron and zinc transport by binding to metal ion transport-related proteins, leading to eliminated biological activities in M. aeruginosa. Meanwhile, 5,4'-DHF inhibit microcystin synthesis and reduce the content of intercellular toxin by inhibiting the transcription of mcyC and binding with McyC protein, implying that 5,4'-DHF have potential to reduce the risk of microcystins in the environment. Moreover, iron starvation and down-regulation of photosynthesis-related genes transcription led to the inhibition of electron transport in photosynthetic system. These results provide more information for the inhibitory mechanism of flavonoids, and the inhibition of flavonoids on metal ion transmembrane transport provides a new perspective for the development of allelochemical algicides.

Can BPA Analogs Affect Cellular and Biochemical Responses in the Microalga Phaeodactylum tricornutum Bohlin?

Bisphenol A analogs (BPA analogs) are emerging contaminants with a rising production caused by the replacement of BPA with these compounds. The increased production of BPA analogs is leading to their increased release into various ecosystems, including marine ones. The aim of this study was to evaluate the biological effects of BPA analogs on a primary producer, the diatom Phaeodactylum tricornutum Bohlin. Three different BPA analogs (BPAF, BPF, and BPS) and their mixture were tested at the environmental relevant concentration of 300 ng/L. Growth, cell size and several biomarkers of oxidative stress and oxidative damage were measured. Our results indicated that the tested compounds caused a reduced growth rate and induced oxidative stress, altering many antioxidant enzymes in P. tricornutum. However, no oxidative damages were observed.

Toxicity effects of disinfection byproduct chloroacetic acid to Microcystis aeruginosa: Cytotoxicity and mechanisms

Chlorine-based disinfectants are widely used for disinfection in wastewater treatment. The mechanism of the effects of chlorinated disinfection by-products on cyanobacteria was unclear. Herein, the physiological effects of chloroacetic acid (CAA) on Microcystis aeruginosa (M. aeruginosa), including acute toxicity, oxidative stress, apoptosis, production of microcystin-LR (MC-LR), and the microcystin transportation-related gene mcyH transcript abundance have been investigated. CAA exposure resulted in a significant change in the cell ultrastructure, including thylakoid damage, disappearance of nucleoid, production of gas vacuoles, increase in starch granule, accumulation of lipid droplets, and disruption of cytoplasm membranes. Meanwhile, the apoptosis rate of M. aeruginosa increased with CAA concentration. The production of MC-LR was affected by CAA, and the transcript abundance of mcyH decreased. Our results suggested that CAA poses acute toxicity to M. aeruginosa, and it could cause oxidative damage, stimulate MC-LR production, and damage cell ultrastructure. This study may provide information about the minimum concentration of CAA in the water environment, which is safe for aquatic organisms, especially during the global coronavirus disease 2019 pandemic period.

Effect of butachlor on Microcystis aeruginosa: Cellular and molecular mechanisms of toxicity

The rapid development of agriculture increases the release of butachlor into aquatic environments. As a dominant species causing cyanobacterial blooms, Microcystis aeruginosa (M. aeruginosa) can produce microcystin and poses threats to aquatic ecosystems and human health. However, the impact of butachlor on M. aeruginosa remains unclarified. Therefore, the physiochemical responses of M. aeruginosa to butachlor were investigated, and the relevant underlying molecular mechanism was highlighted. There were no significant changes (P > 0.05) in the growth and physiology of M. aeruginosa at the low concentrations of butachlor (0-0.1 mg/L), which evidenced a high level of butachlor tolerance in Microcystis aeruginosa. For the high concentrations of butachlor (4-30 mg/L), the inhibition of photosynthetic activity, disruption of cell ultrastructure, and oxidative stress were dominant toxic effects on M. aeruginosa. Additionally, the impaired cellular integrity and lipid peroxidation may be attributed to the substantial elevations of extracellular microcystin-LR concentration. Downregulation of genes associated with photosynthesis, energy metabolism, and oxidative stress was inferred to be responsible for the growth suppression of M. aeruginosa in 30 mg/L butachlor treatment. The upregulation of gene sets involved in nitrogen metabolism may illustrate the specific effort to sustain the steady concentration of intracellular microcystin-LR. These findings dissect the response mechanism of M. aeruginosa to butachlor toxicity and provide valuable reference for the evaluation of potential risk caused by butachlor in aquatic environments.

Triclosan toxicity in a model cyanobacterium (Anabaena flos-aquae): Growth, photosynthesis and transcriptomic response

Exposure to triclosan (TCS) has been reported to reduce photosynthetic pigments, suppress photosynthesis, and inhibit growth in both prokaryotic and eukaryotic algae including Anabaena flos-aquae (a model cyanobacterium). In particular, cyanobacteria are more sensitive to TCS toxicity compared to eukaryotic algae possibly due to the structural similarity to bacteria (target organisms); however, whether TCS exerts its toxicity to cyanobacteria by targeting signaling pathways of fatty acid biosynthesis as in bacteria remains virtually unknown, particularly at environmental exposure levels. With the complete genome sequence of A. flos-aquae presented in this study, the transcriptomic alterations and potential toxic mechanisms in A. flos-aquae under TCS stress were revealed. The growth, pigments and photosynthetic activity of A. flos-aquae were markedly suppressed following a 7-day TCS exposure at 0.5 µg/L but not 0.1 µg/L (both concentrations applied are environmentally relevant). The transcriptomic sequencing analysis showed that signaling pathways, such as biofilm formation - Pseudomonas aeruginosa, two-component system, starch and sucrose metabolism, and photosynthesis were closely related to the TCS-induced growth inhibition in the 0.5 µg/L TCS treatment. Photosynthesis systems and potentially two-component system were identified to be sensitive targets of TCS toxicity in A. flos-aquae. The present study provides novel insights on TCS toxicity at the transcriptomic level in A. flos-aquae.

Aging process does not necessarily enhance the toxicity of polystyrene microplastics to Microcystis aeruginosa

Microplastic (MP) pollution in aquatic systems has attracted increasing attention in recent years. MPs will inevitably encounter aging process in the environment. However, research on the effects of aged MPs on freshwater ecosystems remains limited. This study compared the properties of pristine and aged polystyrene (PS) MPs of different sizes (20 nm, 200 nm, 2000 nm) and determined the effects of aging on the toxicity of PS MPs to typical freshwater cyanobacteria, Microcystis aeruginosa. Aging process induced significant changes to the properties of the MPs, especially their microstructures and surface functional groups. Aging process also influenced zeta potential, which could further affect stability and toxicity of PS MPs. After 96 h exposure, increase of algal growth and photosynthetic activity was observed in the treatment of pristine 200 nm, aged 20 nm and aged 200 nm PS MPs. In addition, pristine 20 nm, pristine 200 nm, pristine 2000 nm, aged 20 nm and aged 200 nm PS MPs were adsorbed on algal cell surface, which could influence the cell permeability. Pristine PS MPs promoted microcystin synthesis and release, which could do harm to drinking water safety and freshwater ecosystems. However, there was no significant increase in aged PS MPs treatments. Furthermore, the increased ¹³C content of algal cells in all pristine PS MPs treatments indicated that M. aeruginosa assimilated more CO₂ and generate more energy to resist the stress of pristine PS MPs when compared with aged PS MPs. These results indicate that aging process did not necessarily enhance the toxicity and biological risk of PS MPs to freshwater ecosystems. Findings of this study fill the knowledge gap in understanding the effects and risks of aged MPs on freshwater ecosystems.

Magnetic-field-induced simultaneous charge separation and oxygen transfer in photocatalytic oxygen activation for algae inactivation

Photocatalytic oxygen activation is an excellent strategy for algae control in water. However, the fast recombination of photogenerated charge and slow rate of oxygen transfer limit the reactive oxygen species generation efficiency for algae inactivation. Herein, to solve above issues, magnetic field was introduced to the BiO_2-x/Bi₃NbO₇ system to effectively covert oxygen into reactive radicals. The electrochemical experiment and DFT calculation results indicated the charge separation could be accelerated by the Lorentz force generated by the magnetic field, resulting in increase of electron concentration. Meanwhile, the value of volumetric gas-liquid mass transfer coefficient was increased by 59.79 % with magnetic field, thus more oxygen could be reduced to superoxide radical. Photocatalytic algae inactivation rate by BiO_2-x/Bi₃NbO₇ with magnetic field could be increased by 2.07 times than that without magnet filed. This work further extends the strategy of using magnetic field to simultaneously facilitate the charge separation and oxygen transfer rate.

Enantioselective effects of chiral fragrance carvone (L- and D-carvone) on the physiology, oxidative damage, synthesis, and release of microcystin-LR in Microcystis aeruginosa

Carvone is a widely used chiral fragrance with two isomers (L-carvone and D-carvone). D-carvone smells like a caraway, whereas L-carvone smells like mint. Carvone imposes a potential burden on the aquatic ecosystem. However, the enantioselective toxic effect of carvone enantiomers on cyanobacteria remains unknown. This study aims to investigate the effects of L- and D-carvone on the physiological processes and related gene transcription (phoU, rbcL, and mcyH) in M. aeruginosa. Results showed that in the presence of L- and D-carvone, the oxidative damage and inhibitory effects on growth occurred in a concentration-dependent manner. The contents of chlorophyll a and protein and the rbcL transcription level were inhibited in M. aeruginosa. In addition, intracellular adenosine triphosphate (ATP) was heavily depleted because of various biological processes, including growth, oxidation reactions, and gene regulation. Meanwhile, L- and D-carvone stimulated the production and release of MC-LR and upregulated the expression level of the MC-LR-related gene mcyH. Intracellular MC-LR likely leaked to the water body under L-carvone exposure, posing a potential threat to the water environment. This study indicated that L- and D-carvone can regulate the physiological and metabolic activity of M. aeruginosa and show enantioselective toxic effects. The findings will also provide important insights into the influence of chiral fragrance on cyanobacterial blooms. Furthermore, this study will guide the safe application of chiral fragrance as personal care products.

Bisphenol-A incite dose-dependent dissimilitude in the growth pattern, physiology, oxidative status, and metabolite profile of Azolla filiculoides

Bisphenol-A (BPA) is a ubiquitous environmental pollutant affecting the growth and development of aquatic macrophytes. The present study was designed to evaluate the toxic effect of BPA on Azolla filiculoides. The plants were exposed to different concentrations of BPA and the effect was evaluated in terms of plant growth, physiological and oxidative status, responses of the antioxidative system, and changes in key metabolites. The results have shown that BPA (≥ 20 mg L^-1) incites a significant reduction in frond number, frond surface area, and growth rate of the plants along with severe frond damage, membrane peroxidation, and electrolyte leakage. Moreover, at higher concentrations, a significant reduction in the content of chlorophylls and carotenoids was observed, which was further amplified with the duration of treatments. Furthermore, excessive generation of O₂^•- and H₂O₂ invoked the antioxidative machinery under BPA exposure. However, sufficient activity of the antioxidative enzymes was observed in plants treated with ≤ 10 mg L^-1 of BPA. The untargeted metabolome profile revealed modulation of 29 metabolites including amino acids, sugar alcohols, organic acids, and phenolics in response to BPA. An increased amount of asparagine, lysine, serine, tryptophan, tyrosine, and valine after 3 days of BPA exposure indicates their role in providing better stress tolerance. Therefore, the experimental findings suggest that A. filiculoides responds differently to BPA exposure. Higher BPA concentrations (≥ 20 mg L^-1) documented a greater impact in terms of plant physiology and metabolism whereas, the effect was minimal at lower concentrations (≤ 10 mg L^-1).

Impact of melatonin on the hydrogen peroxide treatment efficacy in Microcystis aeruginosa: Cell growth, oxidative stress response, and gene transcription

A study was conducted to determine how melatonin (MLT), a growth regulator, affects Microcystis aeruginosa cell behaviour and how MLT exposed cells respond to hydrogen peroxide (H₂O₂) treatment. MLT promotes the growth, chl-a content, Fv/Fm values, and microcystins (MCs) production of M. aeruginosa at low concentrations of 1-2.5 μmol/L but suppresses the growth at high concentrations (5-10 μmol/L). The cellular and genetic responses of MLT pre-treated cells to H₂O₂ treatment were examined further. Further research found that the cells pre-treated with MLT were susceptible to a range of growth-promoting, inhibiting and lethal effects when exposed to higher levels of H₂O₂. A dose-dependent pattern was observed under conditions of 0.05-0.2 mmol/L H₂O₂ with 0.5-2.5 μmol/L MLT concentrations to different degrees. High doses of H₂O₂ (0.2 and 0.3 mmol/L) typically lead to cell lysis and release of MCs in 5.0 and 10 μmol/L MLT pre-treated cells. A decrease in SOD/CAT activities and an increase in MDA levels validated the growth reduction. Furthermore, higher cell lysis and release of intracellular MCs were observed when H₂O₂ was increased for 5-10 μmol/L MLT pre-treated cells. This led to a higher accumulation of extracellular MCs. The results provide insight into how MLT influences H₂O₂ damage and assist in identifying situations where H₂O₂ treatment of cyanobacterial blooms is most appropriate.

Interplay of plastic pollution with algae and plants: hidden danger or a blessing?

In the era of plastic pollution, plants have been discarded as a system that is not affected by micro and nanoplastics, but contrary to beliefs that plants cannot absorb plastic particles, recent research proved otherwise. The presented review gives insight into known aspects of plants' interplay with plastics and how plants' ability to absorb plastic particles can be utilized to remove plastics from water and soil systems. Microplastics usually cannot be absorbed by plant root systems due to their size, but some reports indicate they might enter plant tissues through stomata. On the other hand, nanoparticles can enter plant root systems, and reports of their transport via xylem to upper plant parts have been recorded. Bioaccumulation of nanoplastics in upper plant parts is still not confirmed. The prospects of using biosystems for the remediation of soils contaminated with plastics are still unknown. However, algae could be used to degrade plastic particles in water systems through enzyme facilitated degradation processes. Considering the amount of plastic pollution, especially in the oceans, further research is necessary on the utilization of algae in plastic degradation. Special attention should be given to the research concerning utilization of algae with restricted algal growth, ensuring that a different problem is not induced, "sea blooming", during the degradation of plastics.

Joint toxicity mechanisms of binary emerging PFAS mixture on algae (Chlorella pyrenoidosa) at environmental concentration

Since traditional Per- and polyfluoroalkyl substances (PFAS) were banned in 2009 due to their bioaccumulation, persistence and biological toxicity, the emerging PFAS have been widely used as their substitutes and entered the aquatic environment in the form of mixtures. However, the joint toxicity mechanisms of these emerging PFAS mixtures to aquatic organisms remain largely unknown. Then, based on the testing of growth inhibition, cytotoxicity, photosynthesis and oxidative stress, and the toxicity mechanism of PFAS mixture (Perfluorobutane sulfonate and Perfluorobutane sulfonamide) to algae was explored using the Gene set enrichment analysis (GSEA). The results revealed that all three emerging PFAS treatments had a certain growth inhibitory effect on Chlorella pyrenoidosa (C. pyrenoidosa), but the toxicity of PFAS mixture was stronger than that of individual PFAS and showed a significant synergistic effect at environmental concentration. The joint toxicity mechanisms of binary PFAS mixture to C. pyrenoidosa were related to the damage of photosynthetic system, obstruction of ROS metabolism, and inhibition of DNA replication. Our findings are conductive to adding knowledge in understanding the joint toxicity mechanisms and provide a basis for assessing the environmental risk of emerging PFAS.

Genotoxic potential of bisphenol A: A review

Bisphenol A (BPA), as a major component of some plastic products, is abundant environmental pollutant. Due to its ability to bind to several types of estrogen receptors, it can trigger multiple cellular responses, which can contribute to various manifestations at the organism level. The most studied effect of BPA is endocrine disruption, but recently its prooxidative potential has been confirmed. BPA ability to induce oxidative stress through increased ROS production, altered activity of antioxidant enzymes, or accumulation of oxidation products of biomacromolecules is observed in a wide range of organisms - estrogen receptor-positive and -negative. Subsequently, increased intracellular oxidation can lead to DNA damage induction, represented by oxidative damage, single- and double-strand DNA breaks. Importantly, BPA shows several mechanisms of action and can trigger adverse effects on all organisms inhabiting a wide variety of ecosystem types. Therefore, the main aim of this review is to summarize the genotoxic effects of BPA on organisms across all taxa.

Preparation of freeze-dried bioluminescent bacteria and their application in the detection of acute toxicity of bisphenol A and heavy metals

Current chemical analysis approaches for contaminants have failed to reveal their biotoxicity. Moreover, conventional bioassays are time consuming and exhibit poor repeatability. In this study, we performed the acute toxicity detection of various contaminants (chromium (Cr), cadmium (Cd), lead (Pb), arsenic (As), mercury (Hg), tin (Sn), nickel (Ni), and bisphenol A (BPA)) with four bioluminescent bacteria (Vibrio qinghaiensis Q67, V. fischeri, Photobacterium phosphoreum T3, and P. phosphoreum 502) using a rapid, flexible, and low-cost bioassay. We found that the temperature affected the bacterial luminescence, and freeze-dried cells exhibited sensitive toxic responses to contaminants. Indeed, the optimized protectants containing 12% (w/v) trehalose, 4% sucrose, and 2% sorbitol displayed better luminescence and toxic sensitivity. Furthermore, freeze-dried powders of these strains were prepared and subjected to acute toxicity detection. The results showed that all contaminants exhibited acute toxicity toward Q67, but the other strains did not show obvious response to nickel and tin. The relative half-maximal effective concentration (EC50) values of BPA, Cr, Cd, Pb, As, Hg, Ni, and Sn to Q67 were 0.674, 1.313, 11.137, 5.921, 4.674, 0.911, 5.941, and 54.077 mg/L, respectively. In addition, the EC50 values of contaminants toward different strains were suggested to be statistically significant. Freeze-dried Q67 exhibited toxic responses to more contaminants than the other bioluminescent strains; therefore, Q67 was selected to be more suitable than the other strains for single and mixture toxicity detection tests. Compared with other strains, Q67 was more appropriate for the rapid screening of the mixture toxicity of contaminants in samples as a nonspecific screening sensor before the use of standard analysis approaches.

Acute and Chronic Toxicity of Binary Mixtures of Bisphenol A and Heavy Metals

Bisphenol A (BPA) and heavy metals are widespread contaminants in the environment. However, the combined toxicities of these contaminants are still unknown. In this study, the bioluminescent bacteria Vibrio qinghaiensis Q67 was used to detect the single and combined toxicities of BPA and heavy metals, then the joint effects of these contaminants were evaluated. The results show that chronic toxicities of chromium (Cr), cadmium (Cd), lead (Pb), arsenic (As), mercury (Hg), nickel (Ni), and BPA were time−dependent; in fact, the acute toxicities of these contaminants were stronger than the chronic toxicities. Furthermore, the combined toxicities of BPA and heavy metals displayed BPA + Hg > BPA + Cr > BPA + As > BPA + Ni > BPA + Pb > BPA + Cd in the acute test and BPA + Hg > BPA + Cd > BPA + As > BPA + Cd in the chronic test, which suggested that the combined toxicity of BPA and Hg was stronger than that of other mixtures in acute as well as chronic tests. Additionally, both CA and IA models underestimated the toxicities of mixtures at low concentrations but overestimated them at high concentrations, which indicates that CA and IA models were not suitable to predict the toxicities of mixtures of BPA and heavy metals. Moreover, the joint effects of BPA and heavy metals mainly showed antagonism and additive in the context of acute exposure but synergism and additive in the context of chronic exposure. Indeed, the difference in the joint effects on acute and chronic exposure can be explained by the possibility that mixtures inhibited cell growth and luminescence in chronic cultivation. The chronic toxicity of the mixture should be considered if the mixture results in the inhibition of the growth of cells.

Linear Six-Carbon Sugar Alcohols Induce Lysis of Microcystis aeruginosa NIES-298 Cells

Cyanobacterial blooms are a global concern due to their adverse effects on water quality and human health. Therefore, we examined the effects of various compounds on Microcystis aeruginosa growth. We found that Microcystis aeruginosa NIES-298 cells were lysed rapidly by linear six-carbon sugar alcohols including mannitol, galactitol, iditol, fucitol, and sorbitol, but not by other sugar alcohols. Microscopic observations revealed that mannitol treatment induced crumpled inner membrane, an increase in periplasmic space, uneven cell surface with outer membrane vesicles, disruption of membrane structures, release of intracellular matter including chlorophylls, and eventual cell lysis in strain NIES-298, which differed from the previously proposed cell death modes. Mannitol metabolism, antioxidant-mediated protection of mannitol-induced cell lysis by, and caspase-3 induction in strain NIES-298 were not observed, suggesting that mannitol may not cause organic matter accumulation, oxidative stress, and programmed cell death in M. aeruginosa. No significant transcriptional expression was induced in strain NIES-298 by mannitol treatment, indicating that cell lysis is not induced through transcriptional responses. Mannitol-induced cell lysis may be specific to strain NIES-298 and target a specific component of strain NIES-298. This study will provide a basis for controlling M. aeruginosa growth specifically by non-toxic substances.

Transcriptomic and Physiological Responses of Chlorella pyrenoidosa during Exposure to 17α-Ethinylestradiol

17α-ethinylestradiol (17α-EE₂) is frequently detected in water bodies due to its use being widespread in the treatment of prostate and breast cancer and in the control of alopecia, posing a threat to humans and aquatic organisms. However, studies on its toxicity to Chlorella pyrenoidosa have been limited to date. This study investigated the effects of 17α-EE₂ on the growth, photosynthetic activity, and antioxidant system of C. pyrenoidosa and revealed related molecular changes using transcriptomic analysis. The cell density of algae was inhibited in the presence of 17α-EE₂, and cell morphology was also altered. Photosynthetics were damaged, while reactive oxygen species (ROS), superoxide dismutase (SOD), and malondialdehyde (MDA) content increased. Further transcriptomic analysis revealed that the pathways of photosynthesis and DNA replication were affected at three concentrations of 17α-EE₂, but several specific pathways exhibited various behaviors at different concentrations. Significant changes in differentially expressed genes and their enrichment pathways showed that the low-concentration group was predominantly impaired in photosynthesis, while the higher-concentration groups were biased towards oxidative and DNA damage. This study provides a better understanding of the cellular and molecular variations of microalgae under 17α-EE₂ exposure, contributing to the environmental risk assessment of such hazardous pollutants on aquatic organisms.

Toxicity mechanism of Nylon microplastics on Microcystis aeruginosa through three pathways: Photosynthesis, oxidative stress and energy metabolism

Nylon has been widely used all over the world, and most of it eventually enters the aquatic environment in the form of microplastics (MPs). However, the impact of Nylon MPs on aquatic ecosystem remains largely unknown. Thus, the long-term biological effects and toxicity mechanism of Nylon MPs on Microcystis aeruginosa (M. aeruginosa) were explored in this study. Results demonstrated that Nylon MPs had a dose-dependent growth inhibition of M. aeruginosa at the initial stage, and the maximum inhibition rate reached to 47.62% at the concentration of 100 mg/L. Meanwhile, Nylon MPs could obstruct photosynthesis electron transfer, reduce phycobiliproteins synthesis, destroy algal cell membrane, enhance the release of extracellular polymeric substances, and induce oxidative stress. Furthermore, transcriptomic analysis indicated that Nylon MPs dysregulated the expression of genes involved in tricarboxylic acid cycle, photosynthesis, photosynthesis-antenna proteins, oxidative phosphorylation, carbon fixation in photosynthetic organisms, and porphyrin and chlorophyll metabolism. According to the results of transcriptomic and biochemical analysis, the growth inhibition of M. aeruginosa is inferred to be regulated by three pathways: photosynthesis, oxidative stress, and energy metabolism. Our findings provide new insights into the toxicity mechanism of Nylon MPs on freshwater microalgae and valuable data for risk assessment of MPs.

Environmental estrogens in surface water and their interaction with microalgae: A review

Environmental estrogens (EEs) have received extensive attention because they interfere with biological endocrine and reproduction systems by mimicking, antagonizing, or otherwise affecting the actions of endogenous hormones. Additionally, harmful algal blooms have become a global problem in surface water. Microalgae, as an essential primary producer, is especially important for aquatic life and the entire ecosystem. The presence of EEs in surface water may be a potential promoting factor for algal blooms, and microalgae may have effects on the degradation of EEs. This review focuses on the distribution and pollution characteristics of EEs in global surface waters, effects of single and mixed EEs on microalgae regarding growth and toxin production, mechanisms of EEs on microalgae at the cellular and molecular level. The impacts of microalgae on EEs were also discussed. This review provides a risk assessment of EEs and identifies essential clues that will aid in formulating and revising the relevant standards of surface water regarding EEs, which is significant for ecosystems and human health.

Insights into the underlying mechanisms for integrated inactivation of A. spiroides and depression of disinfection byproducts by plasma oxidation

Cyanobacteria blooms threaten water supply and are potential sources for disinfection byproducts (DBPs) formation. In this study, the underlying mechanisms for effective removal of A. spiroides and the following depression on the formation of DBPs were disclosed. Highly efficient inactivation (more than 99.99%) of A. spiroides was realized by the plasma treatment within 12 min, and 93.4% of Anatoxin-a was also removed within 12 min, with no signals of resurrection after 7 days' re-cultivation. Transcriptomic analysis demonstrated that the expressions of the genes related to cell walls and peripherals, thylakoid membranes, photosynthetic membranes, and detoxification of toxins were distinctly altered. The generated reactive oxidative species (ROS), including ·OH, O₂^·-, and ¹O₂, attacked A. spiroides and resulted in membrane damage and algae organic matter (AOM) release. EEM-PARAFAC analysis illustrated that the AOM compositions were subsequently decomposed by the ROS. As a result, the formation potentials of the C-DBPs and N-DBPs were significantly inhibited, due to the effectively removal of AOM and Anatoxin-a. This study disclosed the underneath mechanisms for the effective inactivation of A. spiroides and inhibition of the following formation of the DBPs, and supplied a prospective technique for integrated pollutant control of cyanobacterial containing drinking water.

Hormones induce the metabolic growth and cytotoxin production of Microcystis aeruginosa under terpinolene stress

Several organic compounds released into the aquatic environment have a detrimental impact on humans and other organisms. There is a lack of knowledge about natural hormones and herbicides on non-target organisms, including cyanobacteria. In this study, the response of Microcystis aeruginosa to four phytohormones, indole-3-acetic acid (IAA; 10^-5), zeatin (ZT; 10^-5), abscisic acid (ABA; 10^-7), and brassinolide (BRL; 10^-9 mol/L), exposed to terpinolene (TPN; (0.44, 0.88, 1.17, or 1.62 mmol/L) at the cellular and genetic levels were investigated. The results showed that TPN could inhibit the growth and photosynthetic activities and stimulate microcystins (MCs) of M. aeruginosa at various levels through the co-occurrence of oxidative stress, antioxidant defense activities, and an imbalance of the antioxidative system. Hormones played critical roles in the growth promotion and photosynthetic activity by enhancing the antioxidant defense mechanisms and MCs production of M. aeruginosa under TPN stress in both hormone and TPN dose-dependent manner. The growth performance and photosynthetic activities of M. aeruginosa were significant with IAA (p < 0.01) and BSL (p < 0.05) compared to ZT and ABA, as TPN concentrations increased. Hormones stimulated the MCs production significantly BSL (p < 0.05) at various levels and protected the cells against TPN-induced oxidative stress and expression of mcyB and mcyD genes involve in MCs synthesis. Our results indicated that hormone contamination in eutrophic lakes might increase the risk of Microcystis aeruginosa bloom and microcystin production with the TPN association.

Efficient integration of plasmonic Ag/AgCl with perovskite-type LaFeO3: Enhanced visible-light photocatalytic activity for removal of harmful algae

A novel plasmonic Ag/AgCl@LaFeO₃ (ALFO) photocatalyst was successfully synthesized by a simple in-situ synthesis method with enhanced photocatalytic activity under visible light for harmful algal blooms (HABs) control. The structure, morphology, chemical states, optical and electrochemical properties of the photocatalyst were systematically investigated using a series of characterization methods. Compared with pure LaFeO₃ and Ag/AgCl, ALFO-20% owned a higher light absorption capacity and lower electron-hole recombined rate. Therefore, ALFO-20% had higher photocatalytic activity with a near 100% removal rate of chlorophyll a within 150 min, whose kinetic constant was 15.36 and 9.61 times faster than those of LaFeO₃ and Ag/AgCl. In addition, the changes of zeta potential, cell membrane permeability, cell morphology, organic matter, total soluble protein, photosynthetic system and antioxidant enzyme system in Microcystis aeruginosa (M. aeruginosa) were studied to explore the mechanism of M. aeruginosa photocatalytic inactivation. The results showed that ALFO-20% could change the permeability and morphology of the algae cell membrane, as well as destroy the photosynthesis system and antioxidant system of M. aeruginosa. What's more, ALFO could further degrade the organic matters flowed out after algae rupture and die, reducing the secondary pollution and avoiding the recurrence of HABs. Finally, the species of reactive oxygen species (ROS) (mainly •O₂^- and •OH) produced by ALFO were determined through quenching experiments, and a possible photocatalytic mechanism was proposed. Overall, ALFO can efficiently remove the harmful algae under the visible light, providing a promising method for controlling HABs.

Mechanisms for the impacts of graphene oxide on the developmental toxicity and endocrine disruption induced by bisphenol A on zebrafish larvae

The huge production and application of bisphenol A (BPA) and graphene oxide (GO) inevitably lead to their co-presence in aquatic ecosystems, which might cause joint toxic effects to aquatic organisms. Herein, zebrafish larvae at 3 d post fertilization (dpf) were exposed to BPA, GO, and their mixtures until 7 dpf. GO was ingested and localized in the gut. 5000 μg/L BPA alone induced distinct ultrastructure damage, which was alleviated by GO, indicating that GO reduced the developmental toxicity of BPA. The levels of endocrine-related genes and steroid hormones were all modulated to the greatest extent by 500 μg/L BPA, suggesting that BPA exhibited a remarkable endocrine disruption effect. However, the responses of some of these genes were recovered by GO, indicating that GO also alleviated the BPA-induced endocrine disruption. The mRNA levels of five genes in the extracellular matrix-receptor interaction pathway, two in the oxidative phosphorylation pathway, 18 in the metabolic pathways, and five in the peroxisome proliferator-activated receptor signaling pathway were distinctly altered by 5000 μg/L BPA, but most of them were recovered in the presence of GO. GO might relieve the BPA-induced developmental toxicity and endocrine disruption by recovering the genes related to the corresponding pathways.

Toxic effects and mechanisms of PFOA and its substitute GenX on the photosynthesis of Chlorella pyrenoidosa

Perfluorooctanoic acid (PFOA) and its substitute GenX are toxic chemicals that are widespread in the aquatic environment. However, there is little information about their toxicity mechanisms to aquatic organisms. In this study, Chlorella pyrenoidosa (C. pyrenoidosa) was treated with two concentrations (100 ng L^-1 and 100 μg L^-1) of PFOA or GenX for 12 days. The results showed that these two concentrations of PFOA and GenX began to inhibit the growth of algae after 6 days of treatment, and the Chlorophyll content and photosynthetic activity of C. pyrenoidosa were also negatively affected by these two chemicals. The transcriptomic results indicated that most of the genes related to the photosynthetic metabolism of C. pyrenoidosa were down-regulated (in 100 ng L^-1 treatment groups) on the 12th day. Besides, GenX and PFOA showed similar effects on algae photosynthesis including physical damage and metabolic disorders. According to this study, GenX might not be an ideal substitute for PFOA, and more attention should be paid on the management of emerging perfluoroalkyl substances.

Proteomic mechanisms for the combined stimulatory effects of glyphosate and antibiotic contaminants on Microcystis aeruginosa

A single exposure to glyphosate or antibiotic may facilitate cyanobacterial growth at currently reported concentrations due to hormesis. However, the influence of these contaminants on cyanobacteria under combined exposure conditions has not been reported. In this study, proteomic mechanisms for the combined effects of glyphosate and a quaternary antibiotic mixture of amoxicillin, sulfamethoxazole, tetracycline, and ciprofloxacin in a dominant bloom-forming cyanobacterium (Microcystis aeruginosa) were investigated and compared with those for single exposure to glyphosate. The growth rate of M. aeruginosa, photosynthetic activity indicated by Fv/Fm, and microcystin production ability showed a typical U-shaped hormetic dose-response to glyphosate exposure. Upregulated proteins related to photosynthesis and biosynthesis, as well as increased photosynthetic activity, were responsible for the stimulated growth induced by 0.1-5 μg/L glyphosate, while the upregulation of mcyB protein contributed to increased microcystin synthesis in glyphosate-treated cells. The presence of 0.04-0.2 μg/L mixed antibiotics significantly (p < 0.05) enhanced the stimulation effects of glyphosate. Combined exposure to glyphosate and mixed antibiotics promoted microcystin synthesis through the upregulation of six microcystin synthesis regulatory proteins (mcyC, mcyF, mcyG, mcyI, MAE_56520, and ntcA) and stimulated cyanobacterial growth through the upregulation of proteins involved in photosynthesis, cell division, carbon fixation, pentose phosphate, translation, and chlorophyll synthesis. Combined exposure to glyphosate and antibiotic contaminants promoted cyanobacterial growth at no-effect concentrations of single exposure (0.04 μg/L for mixed antibiotics; 0.05, 10 and 100 μg/L for glyphosate), suggesting an increased threat from combined contamination to aquatic ecosystems through promoting the formation of cyanobacterial bloom.

Growth inhibition, toxin production and oxidative stress caused by three microplastics in Microcystis aeruginosa

Microplastics (MPs) have aroused widespread concern due to their extensive distribution in aquatic environments and adverse effects on aquatic organisms. However, the underlying toxicity of different kinds of MPs on freshwater microalgae has not been examined in detail. In this study, we investigated the effects of polyvinyl chloride (PVC), polystyrene (PS) and polyethylene (PE) MPs on the growth of Microcystis aeruginosa, as well as on its toxin production and oxidative stress. We found that all three kinds of MPs had an obvious inhibition effect on the growth of M. aeruginosa. Considering the results of antioxidant-related indicators, the activity of superoxide dismutase (SOD) and catalase (CAT), and cell membrane integrity were greatly affected with exposure to PVC, PS and PE MPs. Moreover, the content of intracellular (intra-) and extracellular (extra-) microcystins (MCs) had a noticeable increase due to the presence of PVC, PS, and PE MPs. Finally, according to the comprehensive stress resistance indicators, the resistance of M. aeruginosa to three MPs followed the order: PE (3.701)> PS (3.607)> PVC (2.901). Our results provide insights into the effects of different kinds of MPs on freshwater algae and provide valuable data for risk assessment of different types of MPs.