Cellular and transcriptional responses in Microcystis aeruginosa exposed to two antibiotic contaminants

Responses to phytoplankton community succession and expression of key functional genes in plateau lakes under 17β-estradiol interference

Steroid estrogens (SEs) have garnered global attention because of their potential hazards to human health and aquatic organisms at low concentrations (ng/L). The ecosystems of plateau freshwater lakes are fragile, the water lag time is long, and pollutants easily accumulate, making them more vulnerable to the impact of SEs. However, the knowledge of the impact of SEs on the growth and decomposition of phytoplankton communities in plateau lakes and the eutrophication process is limited. This study investigated the effects and mechanisms of SEs exposure on dominant algal communities and the expression of typical algal functional genes in Erhai Lake using indoor simulations and molecular biological methods. The results showed that phytoplankton were sensitive to 17β-estradiol (E2β) pollution, with a concentration of 50, and 100 ng/L E2β exposure promoting the growth of cyanophyta and chlorophyta in the short term; this poses an ecological risk of inducing algal blooms. E2β of 1000 ng/L exposure led to cross-effects of estrogenic effects and toxicity, with most phytoplankton being inhibited. However, small filamentous cyanobacteria and diatoms exhibited greater tolerance; Melosira sp. even exhibited "low inhibition, high promotion" behavior. Exposure to E2β reduced the Shannon-Wiener diversity index (H'), Pielou index (J), and the number of dominant algal species (S) in phytoplankton communities, leading to instability in community succession. E2β of 50 ng/L enhanced the expression levels of relevant functional genes, such as ftsH, psaB, atpB, and prx, related to Microcystis aeruginosa. E2β of 50 ng/L and 5 mg/L can promote the transcription of Microcystis toxins (MC) related genes (mcyA), leading to more MC production by algal cells.

Effects of clarithromycin exposure on the growth of Microcystis aeruginosa and the production of algal dissolved organic matter

Antibiotics are commonly found in the aquatic environment, which can affect microbial community compositions and activities, and even have potential adverse impacts on human and ecosystem health. The current understanding of the effects of antibiotics on microalgae growth and algal dissolved organic matter (DOM) remains indistinct. To understand the toxic effects of antibiotics on the microalgae, Microcystis aeruginosa was exposed to clarithromycin (CLA) in this study. Cell density determination, chlorophyll content determination, and organic spectrum analysis were conducted to show the effect of CLA exposure on the growth, photosynthetic activity, and organic metabolic processes of Microcystis aeruginosa. The findings revealed that the physiological status of algae could be significantly influenced by CLA exposure in aquatic environments. Specifically, exposure to 1 μg/L CLA stimulated the growth and photosynthetic activity of algal cells. Conversely, CLA above 10 μg/L led to the inhibition of algal cell growth and photosynthesis. Notably, the inhibitory effects intensified with the increasing concentration of CLA. The molecular weight of DOM produced by Microcystis aeruginosa increased when exposed to CLA. Under the exposure of 60 μg/L CLA, a large number of algal cells ruptured and died, and the intracellular organic matter was released into the algal liquid. This resulted in an increase in high molecular weight substances and soluble microbial-like products in the DOM. Exposure to 1 and 10 μg/L CLA stimulated Microcystis aeruginosa to produce more humic acid-like substances, which may be a defense mechanism against CLA. The results were useful for assessing the effects of antibiotic pollution on the stability of the microalgae population and endogenous DOM characteristics in aquatic ecosystems.

The effects of temperature and sulfamethoxazole on the growth and photosynthetic characteristics of Phaeodactylum tricornutum

The misuse of antibiotics has brought potential ecological risks to marine ecosystems, especially under a changing climate. Laboratory experiments were conducted to understand the impact of rising temperatures and antibiotic sulfamethoxazole (SMX) abuse on marine diatom Phaeodactylum tricornutum. Temperatures of 21 and 24 °C were optimal for the growth and photosynthetic characteristics of P. tricornutum. When exposed to higher temperatures (≥27 °C), the growth and photosynthesis were inhibited. High concentrations of SMX (≥100 mg/L) caused rapid and acute toxicological effects on the phytoplankton. In contrast, low concentrations of SMX (1 mg/L) exhibited hormesis. When P. tricornutum was exposed to SMX at high temperatures, the stress on the phytoplankton was even more pronounced. This suggests that the combination of rising temperatures and antibiotic pollution may have a more significant negative impact on marine phytoplankton than either stressor alone. Neglecting the interaction between these stressors may lead to underestimating their combined effects on marine ecosystems.

Investigation of dissolved organic matter's influence on the toxicity of cadmium to the cyanobacterium Microcystis aeruginosa by biochemical and molecular assays

Rapid economic development has increased the accumulation of dissolved organic matter (DOM) and heavy metals in aquatic environments. In addition, Microcystis aeruginosa can cause the outbreak of cyanobacteria bloom and can produce microcystin, which poses a threat to human water safety. Therefore, this study analyzed the biochemical and molecular assays of DOM (0, 1, 3, 5, 8, 10 mg C L-1) extracted from four different sources on the toxicity of cadmium (Cd) to M. aeruginosa. The results showed that the addition of different concentrations of DOM from sediment, biochar, and humic acid alleviated the toxicity of Cd to M. aeruginosa. But the addition of rice hulls DOM at high concentrations (8 and 10 mg L-1) significantly reduced the normal growth and metabolic activities of M. aeruginosa. DOM from four different sources promoted the expression level of microcystin-related gene mcyA and the production of microcystin-leucine-arginine (MC-LR), and mcyA was positively correlated with MC-LR. DOM from biochar, sediment, and humic acid were able to bind Cd through complexation. The results will help to understand the toxic effects of heavy metals on toxic-producing cyanobacteria in the presence of DOM, and provide certain reference for the evaluation of water environmental health.

Long-term tracking robust removal of Microcystis-dominated bloom and microcystin-pollution risk by luteolin continuous-release microsphere at different nitrogen levels-Mechanisms from proteomics and gene expression

Luteolin continuous-release microsphere (CRM) has promising algicidal effect against Microcystis, but how nitrogen (N) level impacted CRM effects on Microcystis growth and microcystins (MCs) pollution was never tracked along long term. This study revealed that luteolin CRM exerted long-term and robust inhibitory effects on Microcystis growth and MC-pollution by sharply decreasing extracellular and total MCs content at each N level, with growth inhibition ratio of 88.18-96.03%, 92.91-97.17% and 91.36-95.55% at 0.5, 5 and 50 mg/L N, respectively, during day 8-30. Further analyses revealed that CRM-stress inhibited transferase, GTPase and ATPase activities, ATP binding, metal ion binding, fatty acid biosynthesis, transmembrane transport and disrupted redox homeostasis to pose equally robust algicidal effect at each N level. At lower N level, CRM-stress tended to induce cellular metabolic mode towards stronger energy supply/acquisition but weaker energy production/consumption, while triggered a shift towards stronger energy production/storage but weaker energy acquisition/consumption as N level elevated, thus disturbing metabolic balance and strongly inhibiting Microcystis growth at each N level. Long-term robust algicidal effect of CRM against other common cyanobacteria besides Microcystis was evident in natural water. This study shed novel insights into inhibitory effects and mechanisms of luteolin CRM on Microcystis growth and MC-pollution in different N-level waters.

Effects of micro- and nano-plastics on accumulation and toxicity of pyrene in water spinach (Ipomoea aquatica Forsk)

Micro- and nano-plastics (MNPs) in terrestrial ecosystems are attracting increasing attentions. However, the studies of MNPs on the accumulation and migration of organic contaminants in edible plants are relatively scarce. Here, we investigated the impacts and mechanisms of MNPs of different concentrations and sizes on the uptake and toxicity of pyrene in water spinach. The results showed that MNPs had a promotion effect on the uptake of pyrene in various parts of water spinach, leading to the continuous accumulation of pyrene. The promotion effect of high concentration microplastics (MPs, 10 μm) is stronger than that of nanoplastics (NPs, 100 nm). The co-exposure of MNPs and pyrene increased the contents of malondialdehyde (MDA) in water spinach and aggravated the damage of lipid peroxidation. The co-exposure of MNPs and pyrene induced the increase of photosynthetic pigment contents and enhanced chloroplast activity. In addition, the co-exposure stimulated the overexpression of psbA and rbcL genes related to photosynthetic pigments, resulting in genotoxicity of water spinach. This study emphasized that the co-exposure of MNPs and pyrene caused harmful effects and high concentration of MPs caused greater toxicity to water spinach than NPs.

Antibiotics degradation by advanced oxidation process (AOPs): Recent advances in ecotoxicity and antibiotic-resistance genes induction of degradation products

Antibiotic contamination could cause serious risks of ecotoxicity and resistance gene induction. Advanced oxidation processes (AOPs) such as Fenton, photocatalysis, activated persulfate, electrochemistry and other AOPs technologies have been proven effective in the degradation of high-risk, refractory organic pollutants such as antibiotics. However, due to the limited mineralization ability, a large number of degradation intermediates will be produced in the oxidation process. The residual or undiscovered ecological risks of degradation products are potential safety hazards and problems necessitating comprehensive studies. In-depth investigations especially on the full assessments of ecotoxicity and resistance genes induction capability of antibiotic degradation products are important issues in reducing the environmental problems of antibiotics. Therefore, this review presents an overview of the current knowledge on the efficiency of different AOPs systems in reducing antibiotics toxicity and antibiotic resistance.

Global review of macrolide antibiotics in the aquatic environment: Sources, occurrence, fate, ecotoxicity, and risk assessment

The extensive use of macrolide antibiotics (MCLs) has led to their frequent detection in aquatic environments, affecting water quality and ecological health. In this study, the sources, global distribution, environmental fate, ecotoxicity and global risk assessment of MCLs were analyzed based on recently published literature. The results revealed that there are eight main sources of MCLs in the water environment. These pollution sources resulted in MCL detection at average or median concentrations of up to 3847 ng/L, and the most polluted water bodies were the receiving waters of wastewater treatment plants (WWTPs) and densely inhabited areas. Considering the environmental fate, adsorption, indirect photodegradation, and bioremoval may be the main attenuation mechanisms in natural water environments. N-demethylation, O-demethylation, sugar and side chain loss from MCL molecules were the main pathways of MCLs photodegradation. Demethylation, phosphorylation, N-oxidation, lactone ring hydrolysis, and sugar loss were the main biodegradation pathways. The median effective concentration values of MCLs for microalgae, crustaceans, fish, and invertebrates were 0.21, 39.30, 106.42, and 28.00 mg/L, respectively. MCLs induced the generation of reactive oxygen species, that caused oxidative stress to biomolecules, and affected gene expression related to photosynthesis, energy metabolism, DNA replication, and repair. Moreover, over 50% of the reported water bodies represented a medium to high risk to microalgae. Further studies on the development of tertiary treatment technologies for antibiotic removal in WWTPs, the combined ecotoxicity of antibiotic mixtures at environmental concentration levels, and the development of accurate ecological risk assessment models should be encouraged.

Effects of Enrofloxacin on the Epiphytic Algal Communities Growing on the Leaf Surface of Vallisneria natans

Enrofloxacin (ENR) is a member of quinolones, which are extensively used in livestock farming and aquaculture to fight various bacterial diseases, but its residues are partially transferred to surface water and affect the local aquatic ecosystem. There are many studies on the effect of ENR on the growth of a single aquatic species, but few on the level of the aquatic community. Epiphytic algae, which are organisms attached to the surface of submerged plants, play an important role in the absorption of nitrogen and phosphorus in the ecological purification pond which are mainly constructed by submerged plants, and are commonly used in aquaculture effluent treatment. Enrofloxacin (ENR) is frequently detected in aquaculture ponds and possibly discharged into the purification pond, thus imposing stress on the pond ecosystem. Here, we performed a microcosm experiment to evaluate the short-term effects of pulsed ENR in different concentrations on the epiphytic algal communities growing on Vallisneria natans. Our results showed an overall pattern of “low-dose-promotion and high-dose-inhibition”, which means under low and median ENR concentrations, the epiphytic algal biomass was promoted, while under high ENR concentrations, the biomass was inhibited. This pattern was mainly attributed to the high tolerance of filamentous green algae and yellow-green algae to ENR. Very low concentrations of ENR also favored the growth of diatoms and cyanobacteria. These results demonstrate a significant alteration of epiphytic algal communities by ENR and also spark further research on the potential use of filamentous green algae for the removal of ENR in contaminated waters because of its high tolerance.

Physiological, biochemical and transcriptional responses of cyanobacteria to environmentally relevant concentrations of a typical antibiotic-roxithromycin

The frequent occurrence of antibiotics in source waters may affect the formation of harmful algal blooms (HABs) dominated by the cyanobacterium Microcystis aeruginosa. However, it remains poorly understood whether dissolved algal organic matters (AOM) can be altered by the introduction of antibiotics in source waters. To resolve these discrepancies, this study investigated the physiological, biochemical, and transcriptional responses of a toxigenic strain of M. aeruginosa to the commonly-detected antibiotic roxithromycin (ROX) at environmentally relevant concentrations ranging from 30 to 8000 ng L^-1. The growth and microcystin (MC) production of M. aeruginosa was significantly stimulated by 300 and 1000 ng L^-1 ROX, whereas inhibited by 5000 and 8000 ng L^-1 ROX. This may be owing to the regulation of genes related to photosynthesis and MCs. Although the membrane of cyanobacterial cells remained intact, the release of MCs was increased significantly with the growing ROX dosages, which may cause additional challenges in drinking water treatment. The amounts of AOM were enhanced by 300 and 1000 ng L^-1 ROX, while decreased by 5000 and 8000 ng L^-1 ROX. It may be attributed to the changes of cyanobacterial cell growth and the gene expression related to carbon fixation, carbohydrate metabolism and nitrogen metabolism. To further understand the regulation of related genes in M. aeruginosa exposed to ROX, trend analysis of differentially expressed genes was performed. The results indicated that the regulation of metabolism-related genes (e.g., lipopolysaccharide biosynthesis) may be also responsible for the changes of cyanobacterial cell densities. Generally, low levels of ROX (300 and 1000 ng L^-1) could stimulated the cyanobacterial growth, MC synthesis and AOM production, which may promote the formation of HABs and reduce the source water quality. Although higher levels of ROX (5000 and 8000 ng L^-1) inhibited the formation of HABs, the threat of increasing extracellular MCs should be considered.

Synergistic toxicity to the toxigenic Microcystis and enhanced microcystin release exposed to polycyclic aromatic hydrocarbon mixtures

With the continued influx and accumulation of polycyclic aromatic hydrocarbons (PAHs) in eutrophic waters, the effects of PAHs on cyanobacteria bloom need to be clarified. PAHs usually existed as mixtures in aquatic environments, but the combined toxicity of PAH mixtures to toxigenic cyanobacteria remained unknown. This study investigated the effects of phenanthrene (Phe) and benzo [a]pyrene (BaP), alone or in combination, on the growth and physiology of Microcystis aeruginosa. The results showed that a hormesis effect on growth at low doses of the single Phe (≤1 mg/L) or PAH mixtures (≤0.279 mg/L) was observed, whereas the single BaP induced significant growth inhibitions at all concentrations (≥0.2 mg/L). The median effective concentrations (96 h) for Phe, BaP and their mixtures were 4.29, 1.29 and 1.07 mg/L, respectively. Mixture toxicity models showed that Phe and BaP elicited a synergistic interaction on M. aeruginosa. The synergy may be ascribed to the excessive oxidative stress induced by PAH mixtures, which further led to membrane structure damages, photosynthesis inhibitions and decreased metabolic activity. Moreover, the microcystins (MCs) release significantly increased by 25.3% and 31.9% upon exposure to 0.558 and 1.116 mg/L of PAH mixtures. In all, this study suggested that the enhanced release of MCs by PAH mixtures might exacerbate potential risks to the aquatic environment.

Effect of protopine exposure on the physiology and gene expression in the bloom-forming cyanobacterium Microcystis aeruginosa

Environment-friendly sound measures with high algal growth inhibition efficiency are required to control and eliminate CyanoHABs. This study examined the effects of protopine on growth, gene expression, and antioxidant system of the M. aeruginosa TY001 and explored possible damage mechanism. The results revealed that higher concentrations of protopine seriously inhibited the growth of M. aeruginosa. Quantitative real-time PCR analysis showed downregulated expression of stress response genes (prx and fabZ), and DNA repair gene (recA) on days 3 and 5. The activities of antioxidant enzymes were also decreased markedly, including superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD). Additionally, protopine stress can significantly increase the malondialdehyde (MDA) level in cells. In conclusion, oxidative damage and DNA damage are the main mechanisms of protopine inhibition on M. aeruginosa TY001. Our studies provide evidence that alkaloid compounds such as protopine may have a potential use value as components of aquatic management strategies.

Micrometer scale polystyrene plastics of varying concentrations and particle sizes inhibit growth and upregulate microcystin-related gene expression in Microcystis aeruginosa

Microplastics (MPs) are a concerning environmental pollutant due to their adverse effects on aquatic organisms. However, the dose- and size-dependent effects of MPs on toxigenic cyanobacteria have not been extensively studied. Herein, we explored the effects of polystyrene MPs (PS-MPs) of varying particle sizes and concentrations on the growth and physiology of Microcystis aeruginosa. The results showed that exposure to 1 µm PS-MPs at a concentration of 2-10 mg L^-1 significantly inhibited the growth of M. aeruginosa in a concentration-dependent manner. After 12 days of exposure, high concentrations of 1 µm PS-MPs (≥ 2 mg L^-1) increased levels of reactive oxygen species. Following exposure to 5 mg L^-1 PS-MPs of different particle sizes, algal growth was inhibited and oxidative stress was induced by 0.5 and 1 µm PS-MPs. At the molecular level, transcription of the atpB gene was generally downregulated in all PS-MPs treatments, while ftsH and fabZ were upregulated. Exposure to PS-MPs also altered the transcription levels of microcystin-related genes (mcyA and mcyH), causing more microcystin to be produced by M. aeruginosa. The results will be useful for understanding the toxicity of MPs toward toxigenic cyanobacteria, and evaluating the ecological risks of MPs in aquatic environments.

Physiological, biochemical and transcription effects of roxithromycin before and after phototransformation in Chlorella pyrenoidosa

Photodegradation is an important transformation pathway for macrolide antibiotics (MCLs) in aquatic environments, but the ecotoxicity of MCLs after phototransformation has not been reported in detail. This study investigated the effects of roxithromycin (ROX) before and after phototransformation on the growth and physio-biochemical characteristics of Chlorella pyrenoidosa, and its toxicity were explored using transcriptomics analysis. The results showed that 2 mg/L ROX before phototransformation (T0 group) inhibited algae growth with inhibition rates of 53.06%, 54.17%, 47.26%, 31.27%, and 28.38% at 3, 7, 10, 14, and 21 d, respectively, and chlorophyll synthesis was also inhibited. The upregulation of antioxidative enzyme activity levels and the malondialdehyde content indicated that ROX caused oxidative damage to C. pyrenoidosa during 21 d of exposure. After phototransformation for 48 h (T48 group), ROX exhibited no significant impact on the growth and physio-biochemical characteristics of the microalgae. Compared with the control group (without ROX and its phototransformation products), 2010 and 2988 differentially expressed genes were identified in the T0 and T48 treatment groups, respectively. ROX significantly downregulated genes related to porphyrin and chlorophyll metabolism, which resulted in the inhibition of chlorophyll synthesis and algae growth. ROX also significantly downregulated genes of DNA replication, suggesting the increased DNA proliferation risks in algae. After phototransformation, ROX upregulated most of the genes associated with the porphyrin and chlorophyll metabolism pathway, which may be the reason that the chlorophyll content in T48 treatment group showed no significant difference from the control group. Almost all light-harvesting chlorophyll a/b (LHCa/b) gene family members were upregulated in both T0 and T48 treatment groups, which may compensate part of the stress of ROX and its phototransformation products.

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.

Antioxidant responses in cyanobacterium Microcystis aeruginosa caused by two commonly used UV filters, benzophenone-1 and benzophenone-3, at environmentally relevant concentrations

Benzophenone-type ultraviolet filters (BPs) have recently been recognized as emerging organic contaminants. In the present study, the cyanobacterium Microcystis aeruginosa was exposed to environmentally relevant levels (0.01-1000 μg L^-1) of benzophenone-1 (BP-1) and benzophenone-3 (BP-3) for seven days. A battery of tested endpoints associated with photosynthetic pigments and oxidative stress was employed for a better understanding of the mode of action. The tested cyanobacterium could uptake the two BPs (27.4-54.9%) from culture media. The two BPs were able to inhibit the production of chlorophyll a (chl-a) and promote the accumulation of carotenoids, leading to unaffected chl-a autofluorescence. Slightly increased malondialdehyde (MDA) contents suggested that BP-1 and BP-3 caused moderate oxidative stress. BP-1 stimulated the activities of superoxide dismutase (SOD), glutathione reductase (GR) and glutathione S-transferase (GST) in M. aeruginosa while BP-3 increased the activities of SOD, GST, and glutathione (GSH), showing a concentration- and time-dependent relationship. The activities of other biomarkers, such as catalase (CAT) and glutathione peroxidase (GPx) fluctuated depending on exposure time and concentration. The overall results suggested that the two BPs can trigger moderate oxidative stress in M. aeruginosa and the tested cyanobacterium was capable of alleviating stress by different mechanisms.

Long-term exposure to antibiotic mixtures favors microcystin synthesis and release in Microcystis aeruginosa with different morphologies

The ecological risks of antibiotics in aquatic environments have raised great concerns worldwide, but the chronic effect of antibiotic contaminants on cyanotoxin production and release remains unclear. This study investigated the long-term combined effects of spiramycin (SP) and ampicillin (AMP) on microcystin (MC) production and release in both unicellular and colonial Microcystis aeruginosa (MA) through semi-continuous exposure test. At exposure concentration of 300 ng L^-1, MA growth rates were stimulated till the end of exponential phase accompanied with the up-regulation of photosynthesis-related gene. The exponential growth phases of unicellular and colonial MA were prolonged for 2 and 4 days, respectively. The stimulation rate of growth rate and MC content in unicellular MA were significantly higher than that in colonial MA. The highest concentrations of intracellular MC (IMC) and extracellular MC (EMC) were observed in the binary mixture at equivalent SP/AMP ratio (1:1). The promotion of IMC concentration was in consistent with the stimulated expression of MC-synthesis-related gene and nitrogen-transport-related gene. The malondialdehyde content and activities of superoxide dismutase and catalase in unicellular MA were significantly higher than those in colonial MA. The EMC concentration and the antioxidant responses of both unicellular and colonial MA significantly increased with exposure time. Long-term exposure to mixture of SA and AMP at environmentally relevant concentrations would aggravate the disturbance to aquatic ecosystem balance through the stimulation of MA proliferation as well as the promotion of MC production and release.

Influence of mixed antibiotics on Microcystis aeruginosa during the application of glyphosate and hydrogen peroxide algaecides

Antibiotics regulate various physiological functions in cyanobacteria and may interfere with the control of cyanobacterial blooms during the application of algaecides. In this study, Microcystis aeruginosa was exposed to H2 O2 and glyphosate for 7 d in the presence of coexisting mixed antibiotics (amoxicillin, spiramycin, tetracycline, ciprofloxacin, and sulfamethoxazole) at an environmentally relevant concentration of 100 ng · L-1 . The mixed antibiotics significantly (P < 0.05) alleviated the growth inhibition effect of 15-45 μM H2 O2 and 40-60 mg · L-1 glyphosate. According to the increased contents of chlorophyll a and protein, decreased content of malondialdehyde, and decreased activities of superoxide dismutase and glutathione S-transferase, antibiotics may reduce the toxicity of the two algaecides through the stimulation of photosynthesis and the reduction in oxidative stress. The presence of coexisting antibiotics stimulated the production and release of microcystins in the M. aeruginosa exposed to low concentrations of algaecides and posed an increased threat to aquatic environments. To eliminate the secondary pollution caused by microcystins, high algaecide doses that are ≥45 μM for H2 O2 and ≥60 mg · L-1 for glyphosate are recommended. This study provides insights into the ecological hazards of antibiotic contaminants and the best management practices for cyanobacterial removal under combined antibiotic pollution conditions.

Toxicological effects of cadmium and lead on two freshwater diatoms

In recent years, there have been significant advances in the knowledge and understanding of the pollution attributed to effects of aquatic toxic metals on fresh water benthic diatoms. In this study, the cell growth, chlorophyll a content and superoxide dismutase activity in Halamphora veneta (Kützing) Levkov and Surirella crumena Brébisson exposed to cadmium and lead, were investigated. Furthermore, in order to explore the potential function of H. veneta on environmental monitoring and environmental remediation, expression of two genes (psbA, psaB) and morphological analysis of H. veneta were carried out. The cells growth of H. veneta and S. crumena were generally inhibited with cadmium and lead exposure during 96 h, while cells density of H. veneta was significantly increased under the low concentration at 24 h cadmium exposure. Our results indicated that H. veneta had a certain tolerance to toxic metals at initial treated time. In addition, the significantly changes of chlorophyll a content and SOD activities in H. veneta and S. crumena indicated that both photosynthetic system and the antioxidant system in benthic diatom might play important roles on the toxic metals tolerant mechanism. Meanwhile, it can be confirmed that the diatom photosynthetic systems play roles on toxic metals resistance inferred from the gene expression of psbA and psaB in H. veneta. Finally, the results of scanning electron microscopy showed that there was a slightly deformation on cells following the cadmium exposure in H. veneta, while obvious deformation with cell greatly widened after lead exposure. The present work will be helpful to understand the effect mechanisms of toxic metal by comparing two kinds of diatom on cell inhibition, biological response and morphological changes, which will provide more information for possible use of benthic diatoms in bioremediation.

Effects of benzophenone-3 on the green alga Chlamydomonas reinhardtii and the cyanobacterium Microcystis aeruginosa

Effects of benzophenone-3 (BP-3) on the green alga, Chlamydomonas reinhardtii, and the cyanobacterium, Microcystis aeruginosa, were investigated. The tested organisms were exposed to environmental levels of BP-3 for 10 days, at nominal concentrations from 0.01 to 5000μgL^-1. Specific growth rate and photosynthetic pigments were employed to evaluate the toxic responses. The two tested algae had distinct toxic responses towards BP-3 stress, with the green alga C. reinhardtii being more sensitive than the cyanobacterium M. aeriginosa, based on EC₂₀ and EC₅₀ values. Uptake of BP-3 from the medium occurred in both species, with M. aeruginosa showing greater overall uptake (27.2-77.4%) compared to C. reinhardtii (1.1-58.4%). The effects of BP-3 on C. reinhardtii were variable at concentrations lower than 100μgL^-1. At higher concentrations, the specific growth rate of C. reinhardtii decreased following a reduction in chlorophyll a (chl-a) content. Further experiments showed that BP-3 regulated the growth of C. reinhardtii by affecting the production of chl-a, chlorophyll b and carotenoids. In M. aeruginosa, specific growth rate was only moderately affected by BP-3. Additionally, the production of chl-a was significantly inhibited over the different exposure concentrations, while the production of carotenoids was stimulated. These results indicate a potential detrimental effect on prokaryotes and eukaryotes and that the mechanism of action varies with species.

Effect of high-doses pyrogallol on oxidative damage, transcriptional responses and microcystins synthesis in Microcystis aeruginosa TY001 (Cyanobacteria)

Severe eutrophication and harmful cyanobacterial blooms of freshwater ecosystems is a persistent environmental topic in recent decades. Pyrogallol (polyphenol) was confirmed to exhibit one of the most intensive inhibitory effects on the Microcystis aeruginosa. In this study, the expression of genes, release of microcystins (MCs) and antioxidant system of pyrogallol on Microcystis aeruginosa TY001 were investigated. The results revealed that the expression of stress response genes (prx, ftsH, grpE and fabZ) and DNA repair genes (recA and gyrB) were up-regulated. Meanwhile, the antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) activity, were increased, and the stress caused lipid peroxidation to occur and malondialdehyde (MDA) levels to change. Unexpectedly, the relative transcript abundance of microcystin synthesis genes (mcyB, mcyD and ntcA) and the contents of microcystins (MCs) significantly increased compared with the control in the culture medium. In conclusion, oxidative damage and DNA damage are the primary mechanisms for the allelopathic effect of pyrogallol on M. aeruginosa TY001.