Effects of glufosinate on antioxidant enzymes, subcellular structure, and gene expression in the unicellular green alga Chlorella vulgaris

Glufosinate-ammonium increased nitrogen and phosphorus content in water and shaped microbial community in epiphytic biofilm of Hydrilla verticillata

Glufosinate-ammonium (GLAM) can be released into adjacent water bodies with rainfall runoff and return water from farmland irrigation. However, impacts of GLAM on aquatic organisms remain unclear. In this study, changes in water quality, plant physiological parameters and epiphytic microbial community were investigated in wetlands with Hydrilla verticillata exposed to GLAM for 24 days. We found GLAM addition damaged cell and reduced chlorophyll a content in Hydrilla verticillata leaves, and increased ammonium and phosphorus in water (p < 0.001). The α-diversity increased in bacterial community but decreased in eukaryotic community with GLAM exposure. Neutral community models explained 62.3 % and 55.0 % of the variance in bacterial and eukaryotic communities, respectively. Many GLAM micro-biomarkers were obtained, including some clades from Proteobacteria, Bacteroidete, Actinobacteriota, Phragmoplastophyta, Annelida and Arthropoda. Redundancy analysis revealed that GLAM concentration was positively correlated to Flavobacterium, Gomphonema and Closterium but negatively to Methyloglobulus and Methylocystis. Network analysis revealed that 15 mg/L GLAM disturbed the interactions among phytoplankton, protozoa, metazoan and bacteria and reduced the stability of the microbial communities compared to 8 mg/L GLAM. GLAM shaped the nitrogen and phosphorus cycle related bacterial genes. This study highlights that herbicides are non-neglectable factors affecting the efficiency of aquatic ecological restoration in agricultural areas to control agricultural non-point source pollution.

What can reactive oxygen species (ROS) tell us about the action mechanism of herbicides and other phytotoxins?

Reactive oxygen species (ROS) are formed in plant cells continuously. When ROS production exceeds the antioxidant capacity of the cells, oxidative stress develops which causes damage of cell components and may even lead to the induction of programmed cell death (PCD). The levels of ROS production increase upon abiotic stress, but also during pathogen attack in response to elicitors, and upon application of toxic compounds such as synthetic herbicides or natural phytotoxins. The commercial value of many synthetic herbicides is based on weed death as result of oxidative stress, and for a number of them, the site and the mechanism of ROS production have been characterized. This review summarizes the current knowledge on ROS production in plants subjected to different groups of synthetic herbicides and natural phytotoxins. We suggest that the use of ROS-specific fluorescent probes and of ROS-specific marker genes can provide important information on the mechanism of action of these toxins. Furthermore, we propose that, apart from oxidative damage, elicitation of ROS-induced PCD is emerging as one of the important processes underlying the action of herbicides and phytotoxins.

Cellular and Genomic Instability Induced by the Herbicide Glufosinate-Ammonium: An In Vitro and In Vivo Approach

Glufosinate-ammonium (GLA), an organophosphate herbicide, is released at high concentrations in the environment, leading to concerns over its potential genotoxic effects. However, few articles are available in the literature reporting the possible cellular and nuclear effects of this compound. We assessed, by in vitro and in vivo micronucleus assays, the genotoxicity of GLA on cultured human lymphocytes and Lymnaea stagnalis hemocytes at six concentrations: 0.010 (the established acceptable daily intake value), 0.020, 0.050, 0.100, 0.200, and 0.500 µg/mL. In human lymphocytes, our results reveal a significant and concentration-dependent increase in micronuclei frequency at concentrations from 0.100 to 0.500 μg/mL, while in L. stagnalis hemocytes, significant differences were found at 0.200 and 0.500 μg/mL. A significant reduction in the proliferation index was observed at all tested concentrations, with the only exception of 0.010 μg/mL, indicating that the exposure to GLA could lead to increased cytotoxic effects. In L. stagnalis, a significant reduction in laid eggs and body growth was also observed at all concentrations. In conclusion, we provided evidence of the genomic and cellular damage induced by GLA on both cultured human lymphocytes and a model organism's hemocytes; in addition, we also demonstrated its effects on cell proliferation and reproductive health in L. stagnalis.

Physiological and molecular mechanisms of the inhibitory effects of artemisinin on Microcystis aeruginosa and Chlorella pyrenoidosa

Artemisinin, a novel plant allelochemical, has attracted attention for its potential selective inhibitory effects on algae, yet to be fully explored. This study compares the sensitivity and action targets of Microcystis aeruginosa (M. aeruginosa) and Chlorella pyrenoidosa (C. pyrenoidosa) to artemisinin algaecide (AMA), highlighting their differences. Results indicate that at high concentrations, AMA displaces the natural PQ at the QB binding site within M. aeruginosa photosynthetic system, impairing the D1 protein repair function. Furthermore, AMA disrupts electron transfer from reduced ferredoxin (Fd) to NADP+ by interfering with the iron-sulfur clusters in the ferredoxin-NADP+ reductases (FNR) domain of Fd. Moreover, significant reactive oxygen species (ROS) accumulation triggers oxidative stress and interrupts the tricarboxylic acid cycle, hindering energy acquisition. Notably, AMA suppresses arginine synthesis in M. aeruginosa, leading to reduced microcystins (MCs) release. Conversely, C. pyrenoidosa counters ROS accumulation via photosynthesis protection, antioxidant defenses, and by regulating intracellular osmotic pressure, accelerating damaged protein degradation, and effectively repairing DNA for cellular detoxification. Additionally, AMA stimulates the expression of DNA replication-related genes, facilitating cell proliferation. Our finding offer a unique approach for selectively eradicating cyanobacteria while preserving beneficial algae, and shed new light on employing eco-friendly algicides with high specificity.

Harnessing the potential of microalgae-based systems for mitigating pesticide pollution and its impact on their metabolism

Due to increased pesticide usage in agriculture, a significant concentration of pesticides is reported in the environment that can directly impact humans, aquatic flora, and fauna. Utilizing microalgae-based systems for pesticide removal is becoming more popular because of their environmentally friendly nature, ability to degrade pesticide molecules into simpler, nontoxic molecules, and cost-effectiveness of the technology. Thus, this review focused on the efficiency, mechanisms, and factors governing pesticide removal using microalgae-based systems and their effect on microalgal metabolism. A wide range of pesticides, like atrazine, cypermethrin, malathion, trichlorfon, thiacloprid, etc., can be effectively removed by different microalgal strains. Some species of Chlorella, Chlamydomonas, Scenedesmus, Nostoc, etc., are documented for >90% removal of different pesticides, mainly through the biodegradation mechanism. The antioxidant enzymes such as ascorbate peroxidase, superoxide dismutase, and catalase, as well as the complex structure of microalgae cell walls, are mainly involved in eliminating pesticides and are also crucial for the defense mechanism of microalgae against reactive oxygen species. However, higher pesticide concentrations may alter the biochemical composition and gene expression associated with microalgal growth and metabolism, which may vary depending on the type of strain, the pesticide type, and the concentration. The final section of this review discussed the challenges and prospects of how microalgae can become a successful tool to remediate pesticides.

Molecular Identification and Phytochemical Analysis and Bioactivity Assessment of Catharanthus roseus Leaf Extract: Exploring Antioxidant Potential and Antimicrobial Activities

Plants have long been at the main focus of the medical industry's attention due to their extensive list of biological and therapeutic properties and ethnobotanical applications. Catharanthus roseus, sometimes referred to as Nithyakalyani in Tamil, is an Apocynaceae family member used in traditional Indian medicine. It also examines the plant's potential antimicrobial and antioxidant activities as well as its preliminary phytochemical makeup. Leaf material from C. roseus was analyzed and found to include a variety of phytochemicals including alkaloids, terpenoids, flavonoids, tannins, phenols, saponins, glycosides, quinones, and steroids. Four of the seven secondary metabolic products discovered in C. roseus leaves showed bioactive principles: 3-methylmannoside, squalene, pentatriacontane, and 2,4,4-trimethyl-3-hydroxymethyl-5a-(3-methyl-but-2-enyl)-cyclohexene. Catharanthus roseus is rich in the anticancer compounds vinblastine and vincristine. Whole DNA was isolated from fresh leaves, then amplified, sequenced, and aligned to find prospective DNA barcode candidates. One DNA marker revealed the restricted genetic relationship among C. roseus based on genetic distance and phylogenetic analysis. The antioxidant activity of the plant extract was evaluated using the DPPH, ABTS, phosphomolybdenum, FRAP, and superoxide radical scavenging activity assays, while the antibacterial potential was evaluated using the agar well diffusion assay. The ethanol extract of C. roseus was found to have the highest reducing power. In addition, a 4- to 21-mm-wide zone of inhibition was seen when the C. roseus extract was tested against bacterial and fungal stains. In conclusion, C. roseus has the most promise as an antibacterial and antioxidant agent.

Length-dependent toxic effects of microplastic fibers on Chlorella pyrenoidosa

Microplastics (MPs), a pervasive pollutant in aquatic environments, are increasingly recognized for their detrimental effects on aquatic organisms. However, the present understanding of their impact on phytoplankton, particularly freshwater microalgae, remains limited. Furthermore, previous studies have predominantly focused on MP particles, largely overlooking the most prevalent form of MPs in aquatic settings-fibers. In this study, we scrutinized the toxicological implications of microplastic fibers (MFs) spanning four distinct lengths (50 μm, 100 μm, 150 μm, and 200 μm) on the protein-nucleated algae Chlorella pyrenoidosa over a six-day period. The study unequivocally demonstrated that MFs markedly impeded C. pyrenoidosa growth, diminished photosynthetic pigment content, and induced oxidative stress, with all observed effects exhibiting a length-dependent correlation. Electron microscopy further revealed notable damage to algal cell membranes. Cell membrane shrinkage, cytoplasm outflow, and abnormalities in cell division were observed in the 150 μm and 200 μm groups. Furthermore, C. pyrenoidosa clustered around the 200 μm MF were notably denser compared to other groups. The present study demonstrated that MFs had length-dependent toxic effects on C. pyrenoidosa. These findings offer novel insights into the deleterious impact of MFs on aquatic organisms, underscoring the pivotal role of length in influencing their toxicity.

Cooperative antioxidative defense of the blue-green alga Arthrospira (Spirulina) platensis under oxidative stress imposed by exogenous application of hydrogen peroxide

Hydrogen peroxide (H2O2) is an environmentally-safe algaecide used to control harmful algal blooms and as a disinfectant in various domestic and industrial applications. It is produced naturally in sunny-water or as a by-product during growth, and metabolism of photosynthetic organisms. To assess the impact of H2O2 on Arthrospira platensis, several biochemical components, and antioxidant enzymes were analysed. The growth and biomass of A. platensis were decreased under the effect of H2O2. Whereas, the concentration up to 40 μM H2O2 non-significantly induced (at P < 0.05) the Chl a, C-phycocyanin (C-PC), total phycobiliprotein (PBP), and the radical scavenging activity of A. platensis. The half-maximal effective concentrations (EC50) for H2O2 were 57, 65, and 74 μM H2O2 with regards to the biomass yield, Chl a, and C-PC content, respectively. While, the total soluble protein, and soluble carbohydrates contents were significantly induced. However, the higher concentrations (60 and 80 μM) were lethal to these components, in parallel to the initiation of the lipid peroxidation process. Surprisingly, the carotenoids content was non-significantly increased by H2O2. Despite the relative consistency of catalase (CAT), the activities of superoxide dismutase (SOD) and peroxidase (POD) enzymes were boosted by all of the tested concentrations of H2O2. The relative transcript abundance of selected regulatory genes was also investigated. Except for the highest dose (80 μM), the tested concentrations had almost inhibitory effect on the relative transcripts of heat shock protein (HSP90), glutamate synthase (GOGAT), delta-9 desaturase (desC), iron-superoxide dismutase (FeSOD) and the Rubisco (the large subunit, rbcL) genes. The results demonstrated the importance of the non-enzymatic and enzymatic antioxidants for the cumulative tolerance of A. platensis.

Keystone microalgae species determine the removal efficiency of sulfamethoxazole: a case study of Chlorella pyrenoidosa and microalgae consortia

In recent years, antibiotics pollution has caused serious harm to the aquatic environment, and microalgae mediated degradation of antibiotics has attracted increasing attention. However, the potential toxicity of antibiotics to keystone microalgae species or their microalgae consortia, and the impact of microalgal diversity on antibiotic removal need to be further studied. In this study, we investigated the removal efficiency and tolerance of five freshwater microalgae (Chlorella pyrenoidosa, Scenedesmus quadricauda, Dictyosphaerium sp., Haematoccocus pluvialis, and Botryococcus braunii) and their microalgae consortia to sulfamethoxazole (SMX). We found that the removal efficiency of SMX by C. pyrenoidosa reached 49%, while the other four microalgae ranged between 9% and 16%. In addition, C. pyrenoidosa, S. quadricauda, and Dictyosphaerium sp. had better tolerance to SMX than H. pluvialis, and their growth and photosynthesis were less affected. At 10 and 50 mg/L SMX, the removal capacity of SMX by mixed microalgae consortia was lower than that of C. pyrenoidos except for the consortium with C. pyrenoidos and S. quadricauda. The consortia generally showed higher sensitivity towards SMX than the individual species, and the biochemical characteristics (photosynthetic pigment, chlorophyll fluorescence parameters, superoxide anion (O₂ ^-), superoxide dismutase activity (SOD), malondialdehyde (MDA) and extracellular enzymes) were significantly influenced by SMX stress. Therefore, the removal of antibiotics by microalgae consortia did not increase with the number of microalgae species. Our study provides a new perspective for the selection of microalgal consortia to degrade antibiotics.

Changes in the morphology and cell ultrastructure of a microalgal community exposed to a commercial glyphosate formulation and a toxigenic cyanobacterium

Human activities significantly influence the health of aquatic ecosystems because many noxious chemical wastes are discharged into freshwater bodies. Intensive agriculture contributes to the deterioration by providing indirectly fertilizers, pesticides, and other agrochemicals that affect the aquatic biota. Glyphosate is one of the most used herbicides worldwide, and microalgae are particularly sensitive to its formulation, inducing displacement of some green microalgae from the phytoplankton that leads to alterations in the floristic composition, which fosters the abundance of cyanobacteria, some of which can be toxigenic. The combination of chemical stressors such as glyphosate and biological ones, like cyanotoxins and other secondary metabolites of cyanobacteria, could induce a combined effect potentially more noxious to microalgae, affecting not only their growth but also their physiology and morphology. In this study, we evaluated the combined effect of glyphosate (Faena^®) and a toxigenic cyanobacterium on the morphology and ultrastructure of microalgae in an experimental phytoplankton community. For this purpose, Microcystis aeruginosa (a cosmopolitan cyanobacterium that forms harmful blooms) and the microalgae Ankistrodesmus falcatus, Chlorella vulgaris, Pseudokirchneriella subcapitata, and Scenedesmus incrassatulus were cultivated, individually and jointly, exposing them to sub-inhibitory concentrations of glyphosate (IC₁₀, IC_20, and IC₄₀). Effects were evaluated through scanning electron (SEM) and transmission electron (TEM) microscopy. Exposure to Faena^® produced alterations in the external morphology and ultrastructure of microalgae both individually and in combined cultures. SEM evidenced the loss of the typical shape and integrity of the cell wall and an increase in the biovolume. TEM revealed reduction and disorganization of the chloroplast, variation in starch and polyphosphate granules, formation of vesicles and vacuoles, cytoplasm degradation, and cell wall continuity loss. The presence of M. aeruginosa was, for microalgae, an additional stress factor adding to the chemical stress produced by Faena^®, increasing the damage in their morphology and ultrastructure. These results alert to the effects that can be caused by glyphosate and the presence of toxigenic bacteria on the algal phytoplankton in contaminated and anthropic and eutrophic freshwater ecosystems.

Enhanced phytotoxicity of 4-chloro-3-Methyphenol and lindane under sodium and potassium salt stresses

Investigating the uptake of organic pollutants by plants under salt stress is critical for evaluating crop contamination, understanding the mechanism of plant uptake, and implementing phytoremediation. The uptake of a highly phytotoxic contaminant, 4-Chloro-3-Methyphenol (CMP, 45 mg L^-1), from solutions by wheat seedling with or without Na⁺ and K⁺ was studied to illustrate the synergistic effect of salt on phytotoxicity of CMP, using uptake kinetics, transpiration, Ca²⁺ leakage and fatty acid saturation as indicators. The influence of Na⁺ and K⁺ on the uptake of lindane, a relatively low toxic contaminant, from soil was also explored. Under CMP-Na⁺ and CMP-K⁺ exposure, the concentrations of CMP in both root and shoot were lower than those under CMP exposure, as a result of the inhibition of transpiration caused by Na⁺ and K⁺ stresses. Low concentration of CMP did not reveal serious toxicity on cell membrane. No apparent difference of MDA generation in root cells was observed, due to the lethal concentration of CMP. The relatively small variation of Ca²⁺ leakage and fatty acid saturation degree in the root cell under exposure of CMP, CMP-Na⁺ and CMP-K⁺, compared to intracellular CMP content, suggested the enhanced phytotoxicity of CMP induced by salt. Higher MDA concentration in shoot cell under CMP-Na⁺ and CMP-K⁺ exposure compared with that under CMP exposure again showed the synergetic toxicity of CMP. High Na⁺ and K⁺ concentration significantly facilitated the uptake of lindane by wheat seedlings in soils, indicating that it could boost the permeability of cell membrane, thereby increasing the toxicity of linande to wheat seedlings. The short-term effect of low salt concentration on the uptake of lindane was not obvious, but long-term exposure also led to increased uptake. In conclusion, the presence of salt could amplify the phtotoxicity of organic contaminant via several mechanisms.

Response of submerged macrophytes and biofilms to coexisting azithromycin and tetracycline: Antibiotic resistance genes removal, toxicity assessment and microbial properties

Antibiotics, such as azithromycin (AZ), tetracycline (TC), and their related antibiotic resistance genes (ARGs), create serious ecological risks to aquatic organisms. This study examined the response mechanisms of submerged macrophytes and periphytic biofilms to a mixture of AZ and TC pollution and determined the antibiotic removal efficiencies and fate of ARGs. The results showed that the plant-biofilm system had a significant capacity for removing both single and combined antibiotics with removal efficiencies of 93.06% ∼99.80% for AZ and 73.35% ∼97.74% for TC. Higher ARG (tetA, tetC, tetW, ermF, ermX, and ermB) abundances were observed in the biofilm, and subsequent exposure to the antibiotic mixture increased the abundances of these genes. Both single and combined antibiotics triggered antioxidant stress, but antagonistic effects were induced only with mixed AZ and TC exposure. Furthermore, the antibiotics changed the structural characteristics of extracellular polysaccharides and induced alterations in the structure of the biofilm microbial community. Increased N-acylated-l-homoserine lactone confirmed alternations in microbial quorum-sensing. The results extend the understanding of the fate of antibiotics and ARGs when aquatic plants and biofilms are exposed to antibiotic mixtures, as well as the organism's response mechanisms.

Response of cytotoxin production ability to gene expression and cell molecular structure of Microcystis aeruginosa FACHB-905

To investigate the inhibitory mechanism of artemisinin sustained-release microspheres (ASMs) on Microcystis aeruginosa (M. aeruginosa) from the molecular level, prx, psbA, fabZ, and mcyD were studied, and the cell death mode were also explored. The results showed that expression of prx was slightly up-regulated, while the expression of psbA, fabZ, and mcyD was significantly reduced. It can infer that oxidant damage and photic damage are the main mechanisms for the algicidal effect of ASMs on M. aeruginosa. It can be seen from the changes in cell morphology and structure that microspheres stress triggers apoptosis-like cell death, and the cell membrane is intact effectively preventing the leakage of microcystin-LR (MC-LR). Moreover, the down-regulation of mcyD gene also played major role in less extracellular MC-LR than intracellular MC-LR. It was concluded that the ASMs will not cause secondary ecological hazards while killing algae cells and have good application prospects.

Acute Toxicity of a Novel anti-fouling Material Additive DCOIT to Marine Chlorella sp

DCOIT (4,5-dichloro-2-n-octyl-4-isothiazolin-3-one) is the main ingredient in SeaNine-211, a new antifouling agent that replaces organotin compounds to prevent the growth of fouling organisms on board. Biocides from antifoulants can cause problems for marine ecosystems by destroying non-target algal species. This study evaluated the potential adverse effects DCOIT using the Marine Chlorella sp. The concentration of DCOIT were set according to the semi-inhibitory concentrations for acute exposure experiments, and relevant oxidative stress indicators were measured to assess the acute toxic effects. The results showed that the inhibition concentrations (IC50) of DCOIT against Marine Chlorella sp was 2.522 mg/L. The genes related to photosynthesis and antioxidant capacity showed the effect of promoting low concentration and inhibiting high concentration. In addition, based on the ultrastructural observation and the expression analysis of photosynthesis related genes, it was found that DCOIT had a significant effect on plant photosynthesis.

The toxic effects of polystyrene microplastics on freshwater algae Chlorella pyrenoidosa depends on the different size of polystyrene microplastics

Microplastics (MPs) are persistent environmental contaminants. The toxic effects of MPs on aquatic organisms have raised increasing concerns, but their toxic effects on aquatic phytoplankton has not been thoroughly investigated. In the present study, the toxic effects of two sizes MPs (1 μm and 5 μm) on Chlorella pyrenoidosa at 2, 10, 50 mg/L were explored for 1, 5, 10 days. The growth ratio, photosynthetic pigments content, extracellular polymeric substances content, soluble protein content, MDA content and relative expression of genes related to photosynthesis and energy metabolism were measured. These results indicated that 1 μm MP could significantly inhibit the growth of C. pyrenoidosa. Compared with the control group, 1 μm MP significantly reduced the photosynthetic pigment content, induced oxidative stress and disrupted the cell membrane integrity of C. pyrenoidosa. At the molecular level, 1 μm MP altered the transcript levels of genes related to photosynthesis and energy metabolism. Scanning electron microscopy and fluorescent images showed that MPs aggregation with C. pyrenoidosa may be the main reason for the toxic effects of MPs. These results will provide new insight into the toxicity of different MPs on aquatic phytoplankton, and evaluate the risks caused by MPs in aquatic environments.

Direct toxicity of the herbicide florasulam against Chlorella vulgaris: An integrated physiological and metabolomic analysis

Herbicides are the agents of choice for use in weed control; however, they can enter the aquatic environment, with potentially serious consequences for non-target organisms. Despite the possible deleterious effects, little information is available regarding the ecotoxicity of the herbicide florasulam toward aquatic organisms. Accordingly, in this study, we investigated the toxic effect of florasulam on the freshwater microalga Chlorella vulgaris and sought to identify the underlying mechanisms. For this, we employed a growth inhibition toxicity test, and then assessed the changes in physiological and metabolomic parameters, including photosynthetic pigment content, antioxidant system, intracellular structure and complexity, and metabolite levels. The results showed that treatment with florasulam for 96 h at the concentration of 2 mg/L, 2.84 mg/L, and 6 mg/L in medium significantly inhibited algal growth and photosynthetic pigment content. Moreover, the levels of reactive oxygen species were also increased, resulting in oxidative damage and the upregulation of the activities of several antioxidant enzymes. Transmission electron microscopic and flow cytometric analysis further demonstrated that exposure to florasulam (6 mg/L) for 96 h disrupted the cell structure of C. vulgaris, characterized by the loss of cell membrane integrity and alterations in cell morphology. Changes in amino acid metabolism, carbohydrate metabolism, and the antioxidant system were also observed and contributed to the suppressive effect of florasulam on the growth of this microalga. Our findings regarding the potential risks of florasulam in aquatic ecosystems provide a reference for the safe application of this herbicide in the environment.

Toxic effects of fludioxonil on the growth, photosynthetic activity, oxidative stress, cell morphology, apoptosis, and metabolism of Chlorella vulgaris

Fludioxonil is widely used in the control of crop diseases because of its broad spectrum and high activity, but its presence is now common in waterways proximate to treated areas. This study examined the toxic effects and mechanisms of fludioxonil on the microalgal taxa Chlorella vulgaris. The results showed that fludioxonil limited the growth of C. vulgaris and the median inhibitory concentration at 96 h was 1.87 mg/L. Concentrations of 0.75 and 3 mg/L fludioxonil reduced the content of photosynthetic pigments in algal cells to different degrees. Fludioxonil induced oxidative damage by altering C. vulgaris antioxidant enzyme activities and increasing reactive oxygen species levels. Fludioxonil at 0.75 mg/L significantly increased the activity of antioxidant enzymes. The highest level of activity was 1.60 times that of the control group. Both fludioxonil treatment groups significantly increased ROS levels, with the highest increase being 1.90 times that of the control group. Transmission electron microscope showed that treatment with 3 mg/L fludioxonil for 96 h disrupted cell integrity and changed cell morphology, and flow cytometer analysis showed that fludioxonil induced apoptosis. Changes in endogenous substances indicated that fludioxonil negatively affects C. vulgaris via altered energy metabolism, biosynthesis of amino acids, and unsaturated fatty acids. This study elucidates the effects of fludioxonil on microalgae and the biological mechanisms of its toxicity, providing insights into the importance of the proper management of this fungicide.

Application of Microalgal Physiological Response as Biomarker for Evaluating the Toxicity of the Textile Dye Alizarin Red S

Textile dyes are becoming a growing threat to the environment. This report presents the findings of the study on the toxicity of the textile dye Alizarin Red S on two freshwater microalgae. The acute toxicity assay revealed that 96-h EC₅₀ values of Chlorella vulgaris and Spirulina platensis were 29.81 mg/L and 18.94 mg/L respectively. The pigments chlorophyll-a, b and carotenoids in C. vulgaris on 96-h exposure to the dye were 2.91, 3.29 and 3.01 times lower in analogy to control whereas Spirulina platensis showed 2.89and 2.56 fold decrease in chlorophyll-a and carotenoid content than control. After the test period of 96-h with dye, the protein content of C. vulgaris and S. platensis were 2.33 and 1.77 times lower compared to the control. The growth inhibition rate, pigment as well as the protein content declined in compliance with the rise in dye concentration, which anticipate paradigm about the toxic effects of the textile dye.

Cadmium Caused Different Toxicity to Photosystem I and Photosystem II of Freshwater Unicellular Algae Chlorella pyrenoidosa (Chlorophyta)

Heavy metals such as Cd pose environmental problems and threats to a variety of organisms. The effects of cadmium (Cd) on the growth and activities of photosystem I (PSI) and photosystem II (PSII) of Chlorella pyrenoidosa were studied. The growth rate of cells treated with 25 and 100 µM of Cd for longer than 48 h were significantly lower than the control, accompanying with the inhibition of photosynthesis. The result of quantum yields and electron transport rates (ETRs) in PSI and PSII showed that Cd had a more serious inhibition on PSII than on PSI. Cd decreased the efficiency of PSII to use the energy under high light with increasing Cd concentration. In contrast, the quantum yield of PSI did not show a significant difference among different Cd treatments. The activation of cyclic electron flow (CEF) and the inhibition of linear electron flow (LEF) due to Cd treatment were observed. The photochemical quantum yield of PSI and the tolerance of ETR of PSI to Cd treatments were due to the activation of CEF around PSI. The activation of CEF also played an important role in induction of non-photochemical quenching (NPQ). The binding features of Cd ions and photosystem particles showed that Cd was easier to combine with PSII than PSI, which may explain the different toxicity of Cd on PSII and PSI.

Toxicological effects of active and inert ingredients of imazethapyr formulation Verosil® against Scenedesmus vacuolatus (Chlorophyta)

Imazethapyr, a selective systemic herbicide, is widely used in agriculture and it is frequently detected in water bodies close to application areas. Like other agrochemicals, imazethapyr is commercialized in formulations containing a mixture of additives that increase the effectiveness of the active ingredient. These complex mixtures may cause adverse effects on non-target primary producers, such as microalgae, when they reach freshwater bodies. The aim of this study was to assess the effects, separately, of the formulation Verosil^®, the formulation additives, and technical-grade imazethapyr, in the acidic form or as ammonium salt, on the microalga Scenedesmus vacuolatus (Chlorophyta). Verosil^®, formulation additives, and acid imazethapyr significantly inhibited the growth of S. vacuolatus (Verosil^® > formulation additives > acid imazethapyr) and caused morphological alterations from 2 mg L^-1, 4 mg L^-1, and 60 mg L^-1 onwards, respectively. Verosil^® and formulation additives caused the most adverse effect including membrane disorganization, cytoplasm contraction, cell wall thickening, thylakoidal membrane disaggregation, and starch granule accumulation. In addition, Verosil^® and formulation additives increased the chl a/chl b ratio, indicating possible alterations in photosystems as a stress response. The carotene/chl a ratio was also increased in microalgae exposed to both Verosil^® and formulation additives, suggesting an antioxidant response to these toxic compounds. All these results support the hypothesis that the formulation additives contribute significantly to the toxicity and alterations caused by the commercial formulation Verosil^® on S. vacuolatus.

Evaluation of the acute toxic response induced by triazophos to the non-target green algae Chlorella pyrenoidosa

Residues of triazophos in aquatic ecosystems due to extensive use for controlling pests in agriculture has became worldwide concern, while the toxic response of triazophos on the non-target green algae in aquatic environment is not well studied. Therefore, the acute (96 h) toxic effects of 1 and 10 mg/L triazophos on green algae Chlorella pyrenoidosa were evaluated in present study. The results showed that the growth was notably inhibited when treated with triazophos and the 96 h-EC₅₀ (median inhibition concentration) were 12.79 mg/L. The content of photosynthetic pigments (including chl a, chl b, total-chl and carotinoids) clearly decreased under two treatments after 48 h and 96 h with exception for the values at 48 h exposure in 1 mg/L treatment. In addition, the transcript abundance of photosynthesis-related genes (psbA, psbC and rbcL) showed obvious decrease in above two treatments after exposure 96 h to triazophos. In response to 10 mg/L triazophos treatment, the morphology of thylakoid chloroplast of algal cells were obviously damaged. It was also found that starch granules increased with down-regulation of atpB gene expression in 10 mg/L treatment, which suggests that triazophos may inhibit the energy metabolism of C. pyrenoidosa. Moreover, the algal growth inhibition was along with the increase of intracellular reactive oxygen species (ROS), activity of antioxidant enzymes and malondialdehyde content indicating oxidative damage and lipid peroxidation in the algal cells. Our findings reveal that triazophos has potential toxicity and environmental risks to one of the primary producers green algae.

A Common Feature of Pesticides: Oxidative Stress-The Role of Oxidative Stress in Pesticide-Induced Toxicity

Pesticides are important chemicals or biological agents that deter or kill pests. The use of pesticides has continued to increase as it is still considered the most effective method to reduce pests and increase crop growth. However, pesticides have other consequences, including potential toxicity to humans and wildlife. Pesticides have been associated with increased risk of cardiovascular disease, cancer, and birth defects. Labels on pesticides also suggest limiting exposure to these hazardous chemicals. Based on experimental evidence, various types of pesticides all seem to have a common effect, the induction of oxidative stress in different cell types and animal models. Pesticide-induced oxidative stress is caused by both reactive oxygen species (ROS) and reactive nitrogen species (RNS), which are associated with several diseases including cancer, inflammation, and cardiovascular and neurodegenerative diseases. ROS and RNS can activate at least five independent signaling pathways including mitochondrial-induced apoptosis. Limited in vitro studies also suggest that exogenous antioxidants can reduce or prevent the deleterious effects of pesticides.

Sesuvium portulacastrum-Mediated Removal of Nitrogen and Phosphorus Affected by Sulfadiazine in Aquaculture Wastewater

Plant-based removal of nitrogen (N) and phosphorus (P) from water bodies is an important method for remediation of aquaculture wastewater. In order to acquire knowledge as to how antibiotic residues in wastewater might affect the microbial community and plant uptake of N and P, this study investigated N and P removal by a coastal plant Sesuvium portulacastrum L. grown in aquaculture wastewater treated with 0, 1, 5, or 50 mg/L sulfonamide antibiotics (sulfadiazine, SD) for 28 days and compared the microbial community structure between the water and rhizosphere. Results showed that SD significantly decreased N removal rates from 87.5% to 22.1% and total P removal rates from 99.6% to 85.5%. Plant fresh weights, root numbers, and moisture contents as well as activities of some enzymes in leaves were also reduced. SD changed the microbial community structure in water, but the microbial community structure in the rhizosphere was less affected by SD. The microbial diversity in water was higher than that in the rhizosphere, indicating microbial community differences. Our results showed that the commonly used antibiotic, SD, in aquaculture can inhibit plant growth, change the structure of microbial community, and reduce the capacity of S. portulacastrum plants to remove N and P from wastewater, and also raised alarm about detrimental effects of antibiotic residues in phytoremediation of wastewater.

Microalgae Chlorella vulgaris and Scenedesmus dimorphus co-cultivation with landfill leachate for pollutant removal and lipid production

In this study, landfill leachate was pre-treated with NaClO, and then diluted to 5%, 10% and 15% for microalgae growth of Chlorella vulgaris and Scenedesmus dimorphus in the mono- and co-culture modes to investigate the nutrient removal and growth characteristics of microalgae. The results revealed that landfill leachate with the 10% dilution rate was conducive for microalgae growth and exhibited robust biomass growth and the highest nutrient removal efficiency. The co-culture biomass in 10% landfill leachate achieved 0.266 g/L within 10 days and demonstrated the improved nutrient utilisation efficiency of microalgae. In addition, the chemical oxygen demand, ammonia nitrogen, total nitrate and total phosphorus removal efficiencies accordingly reached 81.0%, 80.1%, 72.1% and 86.0% in 10% landfill leachate. Meanwhile, both the enzyme activity and fluorescence parameters proved that the cell activity of co-culture was higher than that of mono-culture.

Biochemical and Physiological Responses of Harmful Karenia mikimotoi to Algicidal Bacterium Paracoccus homiensis O-4

Harmful algal blooms caused by Karenia mikimotoi frequently occur worldwide and severely threaten the marine environment. In this study, the biochemical and physiological responses of K. mikimotoi to the algicidal bacterium Paracoccus homiensis O-4 were investigated, and the effects on the levels of reactive oxygen species (ROS), malondialdehyde content, multiple antioxidant systems and metabolites, photosynthetic pigments, and photosynthetic index were examined. The cell-free supernatant in strain O-4 significantly inhibited K. mikimotoi cell growth. The bacterium caused the K. mikimotoi cells to activate their antioxidant defenses to mitigate ROS, and this effect was accompanied by the upregulation of intracellular antioxidant enzymes and non-enzyme systems. However, the overproduction of ROS induced lipid peroxidation and oxidative damage within K. mikimotoi cells, ultimately leading to algal death. In addition, the photosynthetic efficiency of the algal cells was significantly inhibited by O-4 and was accompanied by a reduction in photosynthetic pigments. This study indicates that O-4 inhibits K. mikimotoi through excessive oxidative stress and impaired photosynthesis. This research into the biochemical and physiological responses of K. mikimotoi to algicidal bacteria provides insights into the prophylaxis and control of harmful algal blooms via interactions between harmful algae and algicidal bacteria.

Blocking effect of fullerene nanoparticles (nC60) on the plant cell structure and its phytotoxicity

Blockage of nanoparticles on plant pore structures might produce phytotoxicity and affect plant uptake indirectly. This study examined the blocking and phytotoxic effects of fullerene nanoparticles (nC₆₀) on plants at the cellular level. The malondialdehyde content in plant was normal during nC₆₀ exposure, implying that nC₆₀ caused no acute phytotoxicity, while the normalized relative transpiration significantly decreased, showing that the pore structure of roots was seriously blocked by nC₆₀. High power optical microscopy and transmission electron microscope showed that root endothelial cells were squeezed, and inner wall structures were damaged by the extrusion of nanoparticles. Low nC₆₀ concentrations inhibited root uptake of lindane, whereas high nC₆₀ concentrations promoted root uptake of lindane, indicating that serious pore blocking by nC₆₀ damaged root cell structure and hence ready transport of lindane from roots to shoots. Significant alterations of fatty acid (FA) saturation degree of root cell membrane indicated that nC₆₀ led to phytotoxicity in the root cell membrane after long-term exposure and nC₆₀ produced phytotoxicity in the process of blocking root pore structures and interfering with cell membrane fluidity. Moreover, the plant cell structures under phytotoxicity were more likely to be damaged mechanically by the extrusion of nanoparticles. These findings may be helpful to better understand the transport pathways of nanoparticles in plants, the phytotoxicity of nanoparticles and the potential risks of nanomaterials used in agriculture.

Cartap hydrochloride induced stress response in Anabaena variabilis ARM 441

Cartap hydrochloride is a moderately hazardous nereistoxin analogue insecticide that is predominantly applied in paddy fields of India, at a recommended dose of 10 μg ml^-1 to kill chewing and sucking insect pests of rice crop. Toxicity of cartap hydrochloride was studied on non-target free-living nitrogen fixing cyanobacterium Anabaena variabilis ARM 441 commonly used as algal biofertilizer in rice cultivation. Anabaena sp. could tolerate commercial grade insecticide up to 30 μg ml^-1. However, at the recommended dose of 10 μg ml^-1, it caused reduction in algal growth, total nitrogen and heterocyst frequency by 47.28, 24.29 and 17.72% respectively, as well as photosynthetic pigments under pure culture conditions. Scanning electron micrographs revealed cell rupture and breakage in filaments due to cartap exposure with the formation of akinetes. Cartap hydrochloride induced stress, since level of superoxide dismutase, peroxidase and catalase were increased by 108.57, 187.5 and 117% respectively. Generation of superoxide radicals and hydrogen peroxide were also increased by 152.48 and 34% respectively. Lipid peroxidation was increased by 31.03%, whereas there was decline in ascorbate content by 48.45%, however the glutathione content was increased by 128.57%. Increase in osmolytes such as proline from 8.6 to 32.8% and sucrose from 61.22 to 90.13% indicates their possible role in overcoming cartap induced oxidative stress and can be helpful in assessing its detrimental effect on Anabaena variabilis ARM 441, since cyanobacterial biofertilizers are purposely used in paddy fields as nitrogen contributors.

Lethal and Teratogenic Impacts of Imazapyr, Diquat Dibromide, and Glufosinate Ammonium Herbicide Formulations Using Frog Embryo Teratogenesis Assay-Xenopus (FETAX)

Globally, amphibians are experiencing widespread abnormalities and population declines. One potential contributor to these challenges is the use of pesticides, particularly aquatic herbicides applied to aquatic habitats inhabited by amphibians. Critical issues of concern are the potential toxicity and teratogenicity of these herbicides towards amphibians. Using the FETAX protocol, three globally used formulations, including diquat dibromide (Midstream), glufosinate ammonium (Basta), and imazapyr (Arsenal), were assessed for embryotoxicity, teratogenicity, and growth inhibition. Developing Xenopus laevis embryos were exposed for 96 h at concentrations of 0.5-3.0 mg/L, 1.6-3.0 mg/L, and 20-45 mg/L for Midstream, Basta, and Arsenal respectively. The 96-h LC₅₀ estimates were 0.83 mg/L acid equivalent (a.e.), 36 mg/L a.e., and 2.2 mg/L a.e., whereas the EC₅₀ estimates were 0.24 mg/L a.e., 28.13 mg/L a.e., and 2.01 mg/L a.e. for the Midstream, Arsenal, and Basta formulations, respectively. These two estimates produced Teratogenic Index of 3.5, 1.3, and 1.1 for Midstream, Arsenal, and Basta, respectively, indicating a high risk of malformation induction by Midstream and moderate risk for Arsenal. Regarding growth inhibition, lowest observable effect concentrations of 0.5 mg/L, 25 mg/L, and 2.0 mg/L were computed for Midstream, Arsenal, and Basta, respectively, producing the minimum concentration inhibiting growth (MCIG) ratios of 0.62, 0.69, and 0.89 for the three formulations. These MICG values are higher than the standard 0.30 growth inhibitors benchmark, suggesting that the formulations are not growth inhibitors at the evaluated concentrations. This study provides evidence of the embryotoxic and teratogenic status of Midstream and the embryotoxicity of Basta. There is a need to further characterise the physiological and ecological impacts of these formulations to ensure responsible use and the safety of amphibians and other wildlife.

Photosynthetic and physiological responses to acetochlor in paired near-isogenic lines of waxy maize (Zea mays L.)

Acetochlor is always used in maize (Zea mays L.) fields as a common pre-emergence herbicide. In this field study, we investigated the effects of acetochlor on the photosynthetic characteristics, chlorophyll fluorescence parameters, and antioxidant enzyme activities in acetochlor-resistant (BWC95) and acetochlor-sensitive (BWC12) near-isogenic lines. We sprayed acetochlor after sowing, using water treatment as the control. After spraying acetochlor, the net photosynthetic rate, stomatal conductance, transpiration rate, and the function of chloroplasts were significantly lower in BWC12 than BWC95, whereas the intercellular CO2 concentrations and stomatal limitation values were higher. In addition to nonphotochemical quenching, chlorophyll fluorescence measurements obtained using leaves showed that the maximum photochemical efficiency of photosystem II (PSII), actual photochemical efficiency of PSII, photochemical quenching of chlorophyll fluorescence, and electron transport rate were higher in BWC95 than BWC12 after acetochlor treatment. H2O2 and O2˙- levels were higher in BWC12 than BWC95, which resulted in severe membrane lipid peroxidation due to sustained oxidative stress. Thus, the malondialdehyde content increased significantly with the exposure time in BWC12, and the antioxidant enzyme activities were lower in BWC12 than BWC95. The results show that acetochlor resistance is directly related to a high photosynthetic rate and a protective antioxidant enzyme system.

Acute toxicity of textile dye Methylene blue on growth and metabolism of selected freshwater microalgae

Microalgae are ecologically important species in aquatic ecosystems due to their role as primary producers. The inhibition of growth of microalgae due to dye pollution results in an upheaval in the trophic transfer of nutrients and energy in aquatic ecosystems. Therefore, this investigation aimed to evaluate the toxicity of a textile dye Methylene blue (MB) on two microalgae viz. Chlorella vulgaris and Spirulina platensis. An exposure of the unialgal populations of both the microalgae towards graded concentrations of the dye showed a concentration-dependent decrease in specific growth rate, pigment and protein content. In the toxicity study of 24 -96-h, following the OECD guidelines 201, the EC₅₀ values of C. vulgaris and S. platensis ranged from 61.81 to 5.43 mg/L and 5.83 to 1.08 mg/L respectively revealing that S. platensis exhibited a higher level of susceptibility towards the dye as compared to C. vulgaris and the latter is more tolerant to the dye toxicity even at higher concentrations. The findings indicate that the response to dye is a species-specific phenomenon. Given the differences in the cell structure and enzymatic pathways in Spirulina platensis (a prokaryote) and Chlorella vulgaris (an eukaryote), the tolerance levels can differ. After 96-h exposure of C. vulgaris to MB (100 mg/L), the chlorophyll-a, b and carotenoid content were reduced 2.5, 5.96 and 3.57 times in comparison to control whereas in S. platensis exposure to MB (10 mg/L), the chlorophyll-a and carotenoid content were reduced 3.59 and 5.08 times in comparison to control. After 96-h exposure of C. vulgaris and S. platensis to the dye (20 mg/L), the protein content was found to be 4.34 and 2.75 times lower than the control. The protein content has decreased in accordance with the increase in dye concentration.

Pollutant toxicology with respect to microalgae and cyanobacteria

Microalgae and cyanobacteria are fundamental components of aquatic ecosystems. Pollution in aquatic environment is a worldwide problem. Toxicological research on microalgae and cyanobacteria can help to establish a solid foundation for aquatic ecotoxicological assessments. Algae and cyanobacteria occupy a large proportion of the biomass in aquatic environments; thus, their toxicological responses have been investigated extensively. However, the depth of toxic mechanisms and breadth of toxicological investigations need to be improved. While existing pollutants are being discharged into the environment daily, new ones are also being produced continuously. As a result, the phenomenon of water pollution has become unprecedentedly complex. In this review, we summarize the latest findings on five kinds of aquatic pollutants, namely, metals, nanomaterials, pesticides, pharmaceutical and personal care products (PPCPs), and persistent organic pollutants (POPs). Further, we present information on emerging pollutants such as graphene, microplastics, and ionic liquids. Efforts in studying the toxicological effects of pollutants on microalgae and cyanobacteria must be increased in order to better predict the potential risks posed by these materials to aquatic ecosystems as well as human health.

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

Bisphenol A (BPA), one of the most abundant endocrine-disrupting compounds, is frequently detected in diverse aquatic environments, which imposes a substantial burden on the aquatic ecosystem. However, the correlation between BPA levels and the outbreak of a cyanobacterial bloom remains largely unknown. In this study, the cellular and transcriptomic responses to BPA exposure were investigated. Exposure to a high concentration of BPA (50 μM) significantly inhibited the growth of cyanobacterial cells, with the highest inhibition ratio of 51.3%, photosynthesis, and the release of extracellular microcystin-LR (MC-LR) (p < 0.05). However, exposure to low concentrations of BPA (0.1 and 1 μM) also affected these indicators, but the differences were closely related to the growth phase of the cyanobacterial cells. In addition, an imbalance between the antioxidant system and oxidative stress was observed in cyanobacteria under BPA stress. Folate biosynthesis, ABC transporters and ubiquinone and other terpenoid-quinone biosynthesis were the central metabolic pathways triggered by BPA stress. The up-regulated genes, including queC, VTE3 and PsbO were the controller of cellular growth and photosynthesis. The down-regulated genes, including VET4, MlaE and DnaA were potential biomarkers of oxidative damage. The up- and down-regulated genes, including CA, Ppc and CyoE were the main regulators of energy generation. The findings will provide important insights into the role of endocrine disruptors in the frequent outbreak of cyanobacterial blooms.

Effect of microplastics PAN polymer and/or Cu2+ pollution on the growth of Chlorella pyrenoidosa

Polyacrylonitrile polymer (PAN), a common representative textile material and a microplastic, has significant influence on phytoplankton algae, especially with co-exposure with other pollutants, e.g. Cu²⁺. In the present study, we carried out experiments to reveal the population size variation trends of Chlorella pyrenoidosa over time (during a whole growth cycle of 6 days) under PAN and/or Cu²⁺. The levels of pigments (chlorophyll a, b, total chlorophyll and carotenoids), chlorophyll a fluorescence parameters, and other physiological and biochemical indices, containing total protein measurements of H₂O₂, catalase (CAT), and malondialdehyde (MDA) under different treatment groups were measured to explain the physio-ecological mechanism of the effect of PAN and/or Cu²⁺ on the growth of C. pyrenoidosa. The results showed that PAN, Cu²⁺ and the combination of PAN and Cu²⁺ inhibited the growth of C. pyrenoidosa. Chlorophyll a and b decreased significantly with increasing levels of pollutants (PAN and/or Cu²⁺); however, the carotenoid levels increased with increasing levels of pollutants (PAN and/or Cu²⁺) for the first three cultivation days. The oxygen-evolving complexes (OECs) of C. pyrenoidosa had been damaged under Cu²⁺ pollution. The results also showed that CAT activity, MDA content and H₂O₂ activity of C. pyrenoidosa increased with increasing levels of pollutants (PAN and/or Cu²⁺); however, total protein content decreased with increasing levels of pollutants (PAN and/or Cu²⁺) at the first cultivation day. These results indicate that pollutants (PAN and/or Cu²⁺) are harmful to the growth of the C. pyrenoidosa population and negatively affect the levels and function of the pigments in C. pyrenoidosa by decreasing chlorophyll a and b levels, increasing carotenoid levels, and increasing antioxidant enzyme activity.

Combined effects of 17β-estradiol and copper on growth, biochemical characteristics and pollutant removals of freshwater microalgae Scenedesmus dimorphus

Contamination by estrogens and heavy metals can cause great environment concern and necessitate efficient approaches for their removals. In this study, the combined effects of 17β-estradiol (E2) and Cu(II) on microalgae growth and biochemical characteristics were investigated. Results showed that 1 mg/L Cu(II) promoted the growth of Scenedesmus dimorphus, while 2 mg/L Cu(II) exhibited growth inhibition, compared with the same concentration of E2. Biochemical characteristics including enzyme activities as well as the contents of chlorophyll, protein and carbohydrate were significantly affected by the coexistence of E2 and Cu(II) after 12 d of cultivation. S. dimorphus exhibited high E2 and Cu(II) removal efficiencies (89.9% of E2 and 76.6% Cu(II) under the coexistence of 0.5 mg/L E2 and 1 mg/L Cu(II), respectively). Lower concentration of Cu(II) might serve as a bridge during E2 removal by S. dimorphus while competitive adsorption of Cu(II) and E2 occurred under the condition of excessive Cu(II). Results could confirm that S. dimorphus was a potential bioresource for the effective removal of E2 and Cu(II).

Ecotoxicological effects of sulfonamides and fluoroquinolones and their removal by a green alga (Chlorella vulgaris) and a cyanobacterium (Chrysosporum ovalisporum)

In recent years, antibiotic pollution has become worse, especially in China. In this study, the ecotoxicological effects of four frequently used antibiotics with different lipophilic degrees (log Kow) (sulfadiazine (SD), sulfamethazine (SM2), enrofloxacin (ENR), and norfloxacin (NOR)) at four concentrations of 1, 5, 20, and 50 mg L^-1 were examined using batch cultures of green alga Chlorella vulgaris and cyanobacterium Chrysosporum ovalisporum for 16 days based on changes in chlorophyll fluorescence parameters (chl a, Fv/Fm, and ΦPSII) and responses of the antioxidant system. Besides, the antibiotics removal efficiencies of the two microalgae were investigated. Sulfonamides (SD and SM2) had no significant inhibitory effect on the growth of C. ovalisporum, but had an inhibitory effect on C. vulgaris, whereas fluoroquinolones (ENR and NOR) significantly inhibited C. ovalisporum. The activities of superoxide dismutase, catalase, and glutathione reductase suggested that C. vulgaris was more tolerant to these antibiotics than C. ovalisporum. The increased malondialdehyde level in both algae indicated their tolerance against antibiotics. When compared with C. ovalisporum, C. vulgaris presented better capacity to remove antibiotics. In summary, the four antibiotics exerted time- or concentration-dependent ecotoxicological effects on the microalgae examined, whereas the microalgae could remove the antibiotics based on the log Kow of the antibiotics. The findings of this study contribute to effective understanding of the ecotoxicological effects of antibiotics and their removal by microalgae.

Assessment of oxidative balance in hydrophilic cellular environment in Chlorella vulgaris exposed to glyphosate

The studied hypothesis is that glyphosate (GLY) can affect the oxidative balance in the hydrophilic intracellular medium in non-target Chlorella vulgaris cells. Analytical GLY (5 μM) and a commercial product (RUP) (5 μM) supplementation, did not affect the growth profile. Neither in latent (Lag) nor in exponential (Exp) phase of development, there were significant differences in the cellular abundance, evaluated as cell number, after the supplementation with GLY or RUP. The ascorbyl (A•) content was significantly increased in the presence of GLY or RUP, in Lag and Exp phase of growth. No changes were observed in stationary (St) phase after supplementation with either GLY or RUP. Ascorbate (AH-) content was decreased by 30% in Exp phase of development the presence of RUP. In St phase of the development both, the administration of either GLY or RUP decreased the antioxidant content by 34 and 37%, respectively. The supplementation with GLY and RUP lead to a significant 5- and 10-fold increase in Exp phase, respectively in the A•/AH-content ratio, assessed as a damage/protection ratio in the hydrophilic fraction of the cells, as compared to controls. Neither GLY nor RUP affected the ratio in cells in St phase of development. The data presented here showed experimental evidence that suggested that oxidative balance in the hydrophilic environment is affected by GLY, even at the low to medium concentrations currently used. The effect seems as reversible either because of the magnitude of the herbicide-dependent damage or the antioxidant activity activated.

Effects of mesotrione on oxidative stress, subcellular structure, and membrane integrity in Chlorella vulgaris

Mesotrione is a selective herbicide used to prevent weed attack of corn. It is extensively used, and hence, is being increasingly detected in aquatic ecosystems and may exert adverse effects on aquatic organisms. To evaluate the effects of mesotrione on photosynthesis-related gene expression, antioxidant enzyme activities, subcellular structure, and membrane integrity in algal cells, a comprehensive study was conducted using the green alga, Chlorella vulgaris. Exposure to 4-50 mg/L mesotrione resulted in a progressive inhibition of cell growth, with a 96-h median inhibition concentration (96 h- E_rC₅₀) value of 18.8 mg/L. Further, 18 and 37.5 mg/L mesotrione affected the algal photosynthetic capacity by decreasing the cell pigment content and reducing transcript abundance of photosynthesis-related genes. Mesotrione induced oxidative stress, as confirmed by increased cellular levels of reactive oxygen species (ROS) and malondialdehyde (MDA), and altered antioxidant enzyme activities. It also damaged the algal cellular structure, observed as plasmolysis, blurred organelle shape, and disruption of the chloroplast structure. Flow cytometry analysis revealed that mesotrione exposure led to uneven cell growth and interior irregularities in the algal cell. The apparent propidium iodide (PI) influx also confirmed that the herbicide induced damage of the cell membrane integrity. This study will facilitate the understanding of the physiological and morphological changes induced by mesotrione in C. vulgaris cells, and provide basic information for understanding the biological mechanisms of mesotrione-induced algal toxicity.

Toxicity of microwave-synthesized silver-reduced graphene oxide nanocomposites to the microalga Chlorella vulgaris: Comparison with the hydrothermal method synthesized counterparts

The increased applications of nanomaterials in industry and biomedicine have resulted in a rising concern about their possible toxic impacts on living organisms. It has been claimed that the phytosynthesized nanomaterials have lower toxicity in comparison to their chemically synthesized counterparts. Therefore, it is important to evaluate their toxic effects on the environment. In the present study, we investigated the toxic effects of microwave-synthesized silver-reduced graphene oxide nanocomposites (MS-Ag-rGO) on Chlorella vulgaris. Algal cells were treated by 1, 2, 4 and 6 mg L^-1 MS-Ag-rGO for 24 h. The obtained data with three replicates were examined using analysis of variance. Analysis of different growth parameters revealed that MS-Ag-rGO possessed significant dose-dependent toxic effect on C. vulgaris. Scanning electron microscope and fluorescence microscope images of the treated cells established morphological shrinkages and alteration in position of nucleoli. Moreover, reduction in the phenol and flavonoid contents, enhancement of H₂O₂ content, changes in the antioxidant enzymes activity and decreases in the growth parameters as well as photosynthetic pigments quantities confirmed the toxicity of MS-Ag-rGO to the C. vulgaris cells. Our findings revealed that MS-Ag-rGO possessed higher toxicity on C. vulgaris than Ag-rGO synthesized by hydrothermal technique.

How long-term exposure of environmentally relevant antibiotics may stimulate the growth of Prorocentrum lima: A probable positive factor for red tides

Antibiotics have been widely detected in the ocean and have various impacts on the environment, while knowledge of their chronic influence on phytoplankton, especially red tide algae, is still limited. Dinoflagellates and green algae are common phytoplankton in marine ecosystems. The former is the main red tide algae, and the latter is an important primary producer. We investigated the long-term responses of two representative algae, Prorocentrum lima and Chlorella sp., to two common antibiotics (sulfamethoxazole (SMX) and norfloxacin (NFX)) at environmentally relevant levels (10 and 100 ng/L) during simulated natural conditions. The cell density and activities of three antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD)) were analyzed. The results showed that the influence of each antibiotic on Chlorella sp. was not significant (p > 0.05) during the first 10 days, but the influence of the antibiotics later began to show significant inhibition (p < 0.05) compared with the control group, especially during mixed exposure. P. lima was not inhibited, but its cell density increased. SMX had a superior stimulation effect on P. lima. The three enzymes activities of P. lima increased, and the antioxidant mechanism was not seriously impacted. However, for Chlorella sp., the activity of SOD increased while the activities of CAT and POD decreased, suggesting that this algae's antioxidant system was unbalanced due to oxidative stress. Based on our results, the growth of P. lima was different from green algae Chlorella sp. as well as other inhibited marine algae (such as diatom, golden algae) studied in previous studies. Therefore, as a typical pollutant in the ocean, antibiotics may play a positive role in the bloom of dinoflagellate red tides.

The impact of acute benzo(a)pyrene on antioxidant enzyme and stress-related genes in tropical stony corals (Acropora spp.)

Coral reefs have extremely high ecological value in tropical and subtropical waters worldwide. However, they have been subjected to the most extensive and prolonged damage in recent decades. Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous hazardous pollutants and are highly resistant to degradation in marine environments. Among these compounds, benzo(a)pyrene (BaP) has exerted pressure on corals due to water discharges, oil spills and coastal tourism. In the present study, the physiological response, oxidative stress and stress-related genetic expressions of two Acropora spp. (Acropora formosa and Acropora nasuta) were analysed. These two coral species were exposed to 10 and 40 μg·L^-1 BaP for 24 hand 72 h, respectively. The results show that (1) BaP affects the health of the zooxanthellae in coral symbiosis after BaP exposure for 72 h due to a significant decline in chlorophyll a concentrations in Acropora spp. during this period. (2) An exposure of 10 μg·L^-1 BaP for 24 h induced serious oxidative damage to Acropora spp., with a significant decline and increase in superoxide dismutase (SOD) activities in A. formosa and A. nasuta. (3) The P-gp gene is more sensitive in A. formosa, while the Hsp70 gene is more sensitive in A. nasuta. (4) A. formosa showed a lower ability to resist organic pollutants in coral reefs. Overall, further ecotoxicological studies are needed to investigate the impact of chemical pollutants on corals and to compare their different response mechanisms.

Combined effects of erythromycin and enrofloxacin on antioxidant enzymes and photosynthesis-related gene transcription in Chlorella vulgaris

Multiple antibiotics are simultaneously detected in aquatic environment, so it is extremely important to study the combined effects of their mixtures. In this study, we investigated the toxic effects of erythromycin (ERY) and enrofloxacin (ENR), added individually or in combination, on Chlorella vulgaris and explored the toxic mechanisms. Results showed that the 96 h-EC₅₀ values of ERY, ENR and ERY-ENR mixture to C. vulgaris were 85.7, 124.5 and 39.9 μg L^-1 respectively, and combined toxicity assessment found that joint effect of the two antibiotics was synergism, which was proven by the chlorophyll content in algae. Antioxidant defense system and photosynthesis were involved in toxic mechanisms and the results revealed that both the activities of antioxidant enzymes, and the malondialdehyde (MDA) and glutathione (GSH) contents increased in antibiotic treatments. In addition, the increase was more significant in joint exposure treatment, which implied that the antioxidant defense system was synergistically affected. RT-PCR showed that ERY and ENR upregulated the transcript abundance of psaB, psbC and chlB at low concentrations and the transcription abundance was synergistically increased in combined treatment. Therefore, the risk of the toxicity of antibiotics to aquatic organisms in real environment both at organismal and molecular level increases as a result of their combined presence.

Enantioselective growth inhibition of the green algae (Chlorella vulgaris) induced by two paclobutrazol enantiomers

Enantiomers of chiral pesticides usually display different toxic effects on non-target organisms in surrounding environment, but there are few studies on its enantioselective toxicity of paclobutrazol to aquatic organisms such as Chlorella vulgaris (C. vulgaris). In this study, the enantioselective bioaccumulation and toxicities, such as acute toxicity and oxidative stress, of the racemate, (2S, 3S)-enantiomer (S-enantiomer) and (2R, 3R)-enantiomer (R-enantiomer) of paclobutrazol to the C. vulgaris cells were investigated. The results showed that the algae cells were able to accumulate the paclobutrazol in a short time, while this bioaccumulation had no enantioselective distinction between the two enantiomers during biological metabolism. However, the racemate and two enantiomers of paclobutrazol significantly inhibited the growth of C. vulgaris, displayed different median lethal concentrations. The photosynthetic pigments, photosynthesis-related genes as well as antioxidation-related biomarkers in treated C. vulgaris were also investigated. In general, R-enantiomer was found to be more toxic to C. vulgaris cells than its racemate and S-enantiomer. Additionally, transmission electron microscopy (TEM) analysis showed the R-enantiomer caused more serious changes than S-enantiomer. Moreover, contents of two plant hormones (gibberellin, GA and indoleacetic acid, IAA) were determined in treated C. vulgaris. Higher paclobutrazol concentrations caused lower IAA contents significantly. Nevertheless, the two enantiomers showed no enantioselective effects on the biosynthesis of GA in C. vulgaris. Our results are helpful to understand the enantioselective effects of paclobutrazol enantiomers on non-target organisms, and useful for evaluating their environmental risks.

Effect of glyphosate on the growth, morphology, ultrastructure and metabolism of Scenedesmus vacuolatus

The effects of a commercial glyphosate formulation on the oxidative stress parameters and morphology (including the ultrastructure) of the phytoplanktonic green microalga Scenedesmus vacuolatus were evaluated. After 96 h of exposure to increasing herbicide concentrations (0, 4, 6, 8 mg L-1 active ingredient) with the addition of alkyl aryl polyglycol ether surfactant, the growth of the cultures decreased (96 h-IC50- 4.90 mg L-1) and metabolic and morphology alterations were observed. Significant increases in cellular volume (103-353%) and dry weight (105%) and a significant decrease in pigment content (41-48%) were detected. Oxidative stress parameters were significantly affected, showing an increase in the reactive oxygen species (ROS) and reduced glutathione (GSH) contents, oxidative damage to lipids and proteins and a decrease in the activities of the antioxidant enzymes superoxide dismutase (SOD) and catalase (CAT) and the detoxifying enzyme glutathione-S-transferase (GST). Cells exposed to glyphosate formulation were larger and showed an increase in vacuole size, bleaching, cell wall thickening and alteration of the stacking pattern of thylakoids. The results of this study showed the participation of oxidative stress in the mechanism of toxic action of the commercial glyphosate formulation on S. vacuolatus and the relation between the biochemical, morphological and ultrastructure alterations.

Congo red dye diversely affects organisms of different trophic levels: a comparative study with microalgae, cladocerans, and zebrafish embryos

Global consumption of synthetic dyes is roughly 7 × 10⁵ tons per year, of which the textile industry expends about two-thirds. Consumption of synthetic dyes produces large volumes of wastewater discharged into aquatic ecosystems. Colored effluents produce toxic effects in the hydrobionts, reduce light penetration, and alter the photosynthetic activity, causing oxygen depletion, among other effects. Some dyes, such as Congo red (CR), are elaborated with benzidine, a known carcinogenic compound. Information regarding dye toxicity in aquatic ecosystems is scarce; therefore, our study was aimed at evaluating the toxicity of CR on a battery of bioassays: the microalga Pseudokirchneriella subcapitata, the cladocerans Daphnia magna and Ceriodaphnia rigaudi, and the zebrafish Danio rerio. P. subcapitata was the most sensitive species to CR (IC₅₀, 3.11 mg L^-1); in exposed individuals, population growth was inhibited, but photosynthetic pigments and macromolecule concentrations were stimulated. D. magna was tolerant to high dye concentrations, the determined LC₅₀ (322.9 mg L^-1) is not an environmentally relevant value, but for C. rigaudi, LC₅₀ was significantly lower (62.92 mg L^-1). In zebrafish embryos, exposure to CR produced yolk sac edema, skeletal deformities, and stopped larvae hatching; lack of heart beating was the only observed lethal effect. CR affected organisms of different trophic levels diversely. Particularly, the effects observed in microalgae confirm the vulnerability of primary producers to dye-polluted wastewaters, because dyes produced toxic effects and interfered with photosynthesis. Different cladoceran species displayed different acute effects; thus, species sensitivity must also be considered when toxicity of dyes is assessed. Inhibition of fish larvae hatching is a significant effect not previously reported that warns about the toxicity of dyes in fish population dynamics. Synthetic azo colorants should be considered as emerging pollutants because they are discharged into the aquatic environment and are not currently included in the environmental regulation of several countries.

The influence of four pharmaceuticals on Chlorellapyrenoidosa culture

There has been a developing technology in algae with pharmaceuticals wastewater. However, the effect and the underlying mechanism of pharmaceuticals on algae are not well understood. To investigate the effect and mechanism of pharmaceuticalson microalgae, four pharmaceuticals of clofibric acid (CLF), ciprofloxacin (CIP), diclofenac (DCF) and carbamazepine (CBZ) on C. pyrenoidosa culture were analyzed. At low concentrations (<10 mg/L), the pharmaceuticals, especially the DCF, exhibited positive effects on both the structure and function of algal cultures; algal growth (i.e., chlorophyll a accumulation, lipid accumulation) and activities of antioxidant enzymes were stimulated. The algal metabolite differences of various DCF concentrations were investigated and a total of 91 substances were identified, whose samples were clustered and clearly separated. The key metabolomics pathway analysis found that the DCF promoted the carbohydrate and fatty acid metabolic pathway in C. pyrenoidosa under relatively low concentrations (<10 mg/L). However, the algae metabolomics pathway was disturbed significantly under the action of a high concentration of DCF (>100 mg/L). The study detected the effects of four pharmaceuticals on C. pyrenoidosa and demonstrated that the usage of metabolomics analysis complemented with DCF could be an effective approach to understand the mechanism of molecular evolution in C. pyrenoidosa for microalgal biomass and bioenergy from wastewater in researches of biological resources.

Enantioselective effect of glufosinate on the growth of maize seedlings

Glufosinate is a non-selective chiral herbicide, which has been used extensively around the world. However, limited information on the enantioselectivity of Rac- and L-glufosinate against crops. In this study, the enantioselective effects on the growth, antioxidant, and targeted enzyme activities of maize seedlings of chiral glufosinate were investigated. The results showed the enantioselective growth inhibitions were observed at both 1 and 5 mg/L concentration levels. L-Glufosinate induced more growth rate reduction in shoot height and weight compared to Rac-glufosinate. All of the antioxidant enzyme activities increased obviously in the leaves of maize seedlings treated by 1 mg/L of glufosinate. Superoxide dismutase (SOD) activity, catalase (CAT) activity, peroxidase (POD) activity, glutathione reductase (GR) activity, and malondialdehyde (MDA) content induced by L-glufosinate were 1.36, 1.16, 1.51, 1.65, and 1.65 times higher than those by Rac-glufosinate, respectively Notably, the glutamine synthetase (GS) activity was significantly reduced to 80% and 57% in the control group at 1 mg/L treated with Rac- and L-glufosinate, respectively. Our results indicated that Rac- and L-glufosinate showed the obvious enantioselectivity in the growth of maize seedlings, which has shed light on the potential enantioselective phytotoxicity of glufosinate. Data provided here will be helpful to develop the environmentally friendly herbicides.

Effect of elevated benzophenone-4 (BP4) concentration on Chlorella vulgaris growth and cellular metabolisms

Benzophenone-4 (BP4), as the raw material of common sunscreen products, usually shows strong eco-toxicity and endocrine-disrupting activity in aquatic animals. However, the potential adverse effect of BP4 on aquatic vegetation is still unclear. In order to evaluate the inhibitory effect of BP4 on phytoplankton, wild and acclimated Chlorella vulgaris was used as representative aquatic plant cells and experimental studies were conducted on the characteristics of its growth and cellular metabolisms upon exposure to elevated BP4 concentrations (1, 5, 10, 20, 50, and 100 mg L^-1). C. vulgaris basically appeared low sensitivity to BP4 exposure because the 96-h EC₅₀ was measured as 65.16 mg L^-1 for its wild type. The 96-h EC₅₀ of the acclimated type, which was pre-exposed to 10 mg L^-1 of BP4 and transferred twice, was 140.76 mg L^-1. By cellular response tests regarding non-enzymatic antioxidants carotenoid content, malondialdehyde (MDA), enzyme antioxidant superoxide dismutase (SOD) activity, and the photosynthetic efficiency, it was clarified that increasing exposure concentration elevated the hindrance to cellular metabolism. However, the rate of BP4 utilization as substrates for C. vulgaris growth showed a trend of decreasing with increasing BP4 concentration. The higher 96-h EC₅₀ value of the acclimated C. vulgaris to BP4 inhibition than the wild C. vulgaris showed the enhanced tolerance capability; however, the continuous stress response of acclimated type should be taken into account when using microalgae species for toxicity assessment.

Screening optimal substrates from Erhai lakeside for Ottelia acuminata (Gagnep.) Dandy, an endangered submerged macrophyte in China

Because of the unstable hydrodynamic conditions in the wild, the endangered aquatic plant should be cultivated first in constructed wetlands for the protection and expansion of germplasm resources. Ottelia acuminata (Gagnep.) Dandy has become extinct in Erhai Lake, Yunnan province, China. In order to optimize substrates for this species to artificial cultivation, the native substrate (sandy soils) and the other three representative ones (red paddy soils, alluvial paddy soils, and purple paddy soils) collected from Erhai lakeside were applied to cultivate O. acuminata for 50 days. Multi indicators, such as antioxidant enzymes activity, malondialdehyde and chlorophyll-α concentration, and relative growth rate of O. acuminata, were discussed and statistically analyzed to classify the substrates. The results suggested that even disregarding the physiology significance of these indicators, hierarchical clustering analysis had high efficiency on optimizing substrates. Although various single indexes suggested different optimal substrates for macrophyte growth, red paddy soil was never excluded out the optimal substrate classes. Further study is needed to assess the substrates optimization functionalities of these indicators. This study offers amounts of physiology data and an effective method to optimize substrates of O. acuminata. It is helpful for environmental scientists and ecological engineers to conduct the similar study on endangered species.