Understanding the influence of glyphosate on the structure and function of freshwater microbial community in a microcosm

Impacts of organophosphate pesticide types and concentrations on aquatic bacterial communities and carbon cycling

Organophosphorus pesticides (OPPs) are important chemical stressors in aquatic ecosystems, and they attract increasing more attentions recently. However, the impacts of different OPPs on carbon cycling remain unclear, particularly for those functional-yet-uncultivable microbes. This study investigated the change in lake aquatic microbial communities in the presence of dichlorvos, monocrotophos, omethoate and parathion. All OPPs significantly inhibited biomass (p < 0.05) and the expression of carbon cycle-related cbbLG gene (p < 0.01), and altered aquatic microbial community structure, interaction, and assembly. Variance partitioning analysis showed a stronger impact of pesticide type on microbial biomass and community structure, where pesticide concentration played more significant roles in carbon cycling. From analysis of cbbLG gene and PICRUSt2, Luteolibacter and Verrucomicrobiaceae assimilated inorganic carbon through Wood-Ljungdahl pathway, whereas it was Calvin-Benson-Bassham cycle for Cyanobium PCC-6307. This work provides a deeper insight into the behavior and mechanisms of microbial community change in aquatic system in response to OPPs, and explicitly unravels the impacts of OPPs on their carbon-cycling functions.

Common use herbicides increase wetland greenhouse gas emissions

Wetlands play a disproportionate role in the global climate as major sources and sinks of greenhouse gases. Herbicides are the most heavily used agrochemicals and are frequently detected in aquatic ecosystems, with glyphosate and 2,4-Dichlorophenoxyacetic acid (2,4-D), representing the two most commonly used worldwide. In recent years, these herbicides are being used in mixtures to combat herbicide-tolerant noxious weeds. While it is well documented that herbicide use for agriculture is expected to increase, their indirect effects on wetland greenhouse gas dynamics are virtually unknown. To fill this knowledge gap, we conducted a factorial microcosm experiment using low, medium, and high concentrations of glyphosate or 2,4-D, individually and in combination to investigate their effects on wetland methane, carbon dioxide, and nitrous oxide fluxes. We predicted that mixed herbicide treatments would have a synergistic effect on greenhouse gases compared to individual herbicides. Our results showed that carbon dioxide flux rates and cumulative emissions significantly increased from both individual and mixed herbicide treatments, whereas methane and nitrous oxide dynamics were less affected. This study suggests that extensive use of glyphosate and 2,4-D may increase carbon dioxide emissions from wetlands, which could have implications for climate change.

Microbial community structure and co-occurrence network stability in seawater and microplastic biofilms under prometryn pollution in marine ecosystems

Prometryn has been extensively detected in marine environment because of its widespread usage in agriculture and aquaculture and has been concerns since its serious effects on aquatic organisms. However, its impact on the microbial community in the marine ecosystem including seawater and biofilm is still unclear. Therefore, a short-term indoor microcosm experiment of prometryn exposure was conducted. This study found that prometryn had a more significant impact on the structure and stability of the microbial community in seawater compared to microplastic biofilms. Additionally, we observed that the assembly of the microbial community in biofilms was more affected by stochastic processes than in seawater under the exposure of prometryn. Our study provided evidence for the increasing impact of the microbial communities under the stress of prometryn and microplastics.

Ketoprofen exposure perturbs nitrogen assimilation and ATP synthesis in rice roots: An integrated metabolome and microbiome analysis

Ketoprofen, a commonly used non-steroidal anti-inflammatory drug (NSAID), can enter farmland environments via sewage irrigation and manure application and is toxic to plants. However, there have been relatively few studies on the association of ketoprofen with nitrogen (N) assimilation and metabolic responses in plants. Accordingly, the goal of this study was to investigate the effects of ketoprofen on ATP synthesis and N assimilation in rice roots. The results showed that with increasing ketoprofen concentration, root vitality, respiration rate, ATP content, and H+-ATPase activity decreased and plasma membrane permeability increased. The expressions of OSA9, a family III H+-ATPase gene, and OSA6 and OSA10, family IV genes, were upregulated, indicating a response of the roots to ketoprofen. Nitrate, ammonium, and free amino acids content decreased with increased ketoprofen. The levels of enzymes involved in N metabolism, namely nitrate reductase, nitrite reductase, glutamine synthetase, glutamate synthetase, and glutamate dehydrogenase, also decreased under ketoprofen treatment. Principal component analysis revealed that ketoprofen treatment can significantly affect energy synthesis and nitrogen assimilation in rice roots, while these effects can be alleviated by the antioxidant response. Most of the metabolite contents increased, including amino acids, carbohydrates, and secondary metabolites. Key metabolic pathways, namely substance synthesis and energy metabolism, were found to be disrupted. Microbiome analysis showed that community diversity and richness of rice root microorganisms in solution increased with increasing levels of ketoprofen treatment, and the microbial community structure and metabolic pathways significantly changed. The results of this study provides new insights into the response of rice roots to ketoprofen.

How Benthic Sediment Microbial Communities Respond to Glyphosate and Its Metabolite: a Microcosm Experiment

Glyphosate is the most commonly used agricultural herbicide in the world. In aquatic ecosystems, glyphosate often adsorbs to benthic substrates or is metabolized and degraded by microorganisms. The effects of glyphosate on microbial communities vary widely as microorganisms respond differently to exposure. To help understand the impacts of glyphosate on the sediment microbiome, we conducted a microcosm experiment examining the responses of benthic sediment microbial communities to herbicide treatments. Sediments from a prairie pothole wetland were collected, and 16S rRNA gene sequencing was used to analyze community composition 2-h and 14-days after a single treatment of low (0.07 ppm), medium (0.7 ppm), or high (7 ppm) glyphosate, aminomethylphosphonic acid (glyphosate metabolite), or a glyphosate-based commercial formula. We found no significant differences in microbial community composition across treatments, concentration levels, or day of sampling. These findings suggest that microbial species in the Prairie Pothole Region of North America may be tolerant to glyphosate exposure.

A global atlas of marine antibiotic resistance genes and their expression

Oceans serve as global reservoirs of antibiotic-resistant bacteria and antibiotic resistance genes (ARGs). However, little is known about the traits and expression of ARGs in response to environmental factors. We analyzed 347 metagenomes and 182 metatranscriptomes to determine the distribution, hosts, and expression of ARGs in oceans. Our study found that the diversity and abundance of ARGs varied with latitude and depth. The core marine resistome mainly conferred glycopeptide and multidrug resistance. The hosts of this resistome were mainly limited to the core marine microbiome, with phylogenetic barriers to the horizontal transfer of ARGs, transfers being more frequent within species than between species. Sixty-five percent of the marine ARGs identified were expressed. More than 90% of high-risk ARGs were more likely to be expressed. Anthropogenic activity might affect the expression of ARGs by altering nitrate and phosphate concentrations and ocean temperature. Machine-learning models predict >97% of marine ARGs will change expression by 2100. High-risk ARGs will shift to low latitudes and regions with high anthropogenic activity, such as the Pacific and Atlantic Oceans. Certain ARGs serve a dual role in antibiotic resistance and potentially participate in element cycling, along with other unknown functions. Determining whether changes in ARG expression are beneficial to ecosystems and human health is challenging without comprehensive understanding of their functions. Our study identified a core resistome in the oceans and quantified the expression of ARGs for the development of future control strategies under global change.

Photodegradation of glyphosate in water and stimulation of by-products on algae growth

Glyphosate is the most widely used herbicide in global agricultural cultivation. However, little is known about the environmental risks associated with its migration and transformation. We conducted light irradiation experiments to study the dynamics and mechanism of photodegradation of glyphosate in ditches, ponds and lakes, and evaluated the effect of glyphosate photodegradation on algae growth through algae culture experiments. Our results showed that glyphosate in ditches, ponds and lakes could undergo photochemical degradation under sunlight irradiation with the production of phosphate, and the photodegradation rate of glyphosate in ditches could reach 86% after 96 h under sunlight irradiation. Hydroxyl radicals (•OH) was the main reactive oxygen species (ROS) for glyphosate photodegradation, and its steady-state concentrations in ditches, ponds and lakes were 6.22 × 10-17, 4.73 × 10-17, and 4.90 × 10-17 M. The fluorescence emission-excitation matrix (EEM) and other technologies further indicated that the humus components in dissolved organic matter (DOM) and nitrite were the main photosensitive substances producing •OH. In addition, the phosphate generated by glyphosate photodegradation could greatly promote the growth of Microcystis aeruginosa, thereby increasing the risk of eutrophication. Thus, glyphosate should be scientifically and reasonably applied to avoid environmental risks.

Twenty Years of Research in Ecosystem Functions in Aquatic Microbial Ecotoxicology

One of the major threats to freshwater biodiversity is water pollution including excessive loads of nutrients, pesticides, industrial chemicals, and/or emerging contaminants. The widespread use of organic pesticides for agricultural and nonagricultural (industry, gardening, etc.) purposes has resulted in the presence of their residues in various environments, including surface waters. However, the contribution of pesticides to the deterioration of freshwater ecosystems (i.e., biodiversity decline and ecosystem functions impairment) remains uncertain. Once in the aquatic environment, pesticides and their metabolites can interact with microbial communities, causing undesirable effects. The existing legislation on ecological quality assessment of water bodies in Europe is based on water chemical quality and biological indicator species (Water Framework Directive, Pesticides Directive), while biological functions are not yet included in monitoring programs. In the present literature review, we analyze 20 years (2000-2020) of research on ecological functions provided by microorganisms in aquatic ecosystems. We describe the set of ecosystem functions investigated in these studies and the range of endpoints used to establish causal relationships between pesticide exposure and microbial responses. We focus on studies addressing the effects of pesticides at environmentally realistic concentrations and at the microbial community level to inform the ecological relevance of the ecotoxicological assessment. Our literature review highlights that most studies were performed using benthic freshwater organisms and that autotrophic and heterotrophic communities are most often studied separately, usually testing the pesticides that target the main microbial component (i.e., herbicides for autotrophs and fungicides for heterotrophs). Overall, most studies demonstrate deleterious impacts on the functions studied, but our review points to the following shortcomings: (1) the nonsystematic analysis of microbial functions supporting aquatic ecosystems functioning, (2) the study of ecosystem functions (i.e., nutrient cycling) via proxies (i.e., potential extracellular enzymatic activity measurements) which are sometimes disconnected from the current ecosystem functions, and (3) the lack of consideration of chronic exposures to assess the impact of, adaptations to, or recovery of aquatic microbial communities from pesticides. Environ Toxicol Chem 2023;42:1867-1888. © 2023 SETAC.

Chemodiversity of Cyanobacterial Toxins Driven by Future Scenarios of Climate Warming and Eutrophication

Climate change and eutrophication are two environmental threats that can alter the structure of freshwater ecosystems and their service functions, but we know little about how ecosystem structure and function will evolve in future scenarios of climate warming. Therefore, we created different experimental climate scenarios, including present-day conditions, a 3.0 °C increase in mean temperature, and a "heatwaves" scenario (i.e., an increase in temperature variability) to assess the effects of climate change on phytoplankton communities under simultaneous stress from eutrophication and herbicides. We show that the effects of climate warming, particularly heatwaves, are associated with elevated cyanobacterial abundances and toxin production, driven by a change from mainly nontoxic to toxic Microcystis spp. The reason for higher cyanobacterial toxin concentrations is likely an increase in abundances because under the dual pressures of climate warming and eutrophication individual Microcystis toxin-producing ability decreased. Eutrophication and higher temperatures significantly increased the biomass of Microcystis, leading to an increase in the cyanobacterial toxin concentrations. In contrast, warming alone did not produce higher cyanobacterial abundances or cyanobacterial toxin concentrations likely due to the depletion of the available nutrient pool. Similarly, the herbicide glyphosate alone did not affect abundances of any phytoplankton taxa. In the case of nutrient enrichment, cyanobacterial toxin concentrations were much higher than under warming alone due to a strong boost in biomass of potential cyanobacterial toxin producers. From a broader perspective our study shows that in a future warmer climate, nutrient loading has to be reduced if toxic cyanobacterial dominance is to be controlled.

The mechanism of different cyanobacterial responses to glyphosate

Glyphosate, the most extensively used herbicide globally, has raised ecotoxicological concerns because it can be transported into the aquatic environment and cause adverse effects on the aquatic system. However, the functional mechanism of glyphosate on cyanobacteria are not completely disentangled. In this study, we selected six common cyanobacteria to evaluate glyphosate effects on cyanobacterial growth in monoculture experiment. Results showed that the growth of five tested cyanobacterial species were promoted under different degrees, and only Pseudanabaena was inhibited by glyphosate. In the phylogenetic tree based on gene sequences of 5-enol-pyruvylshikimate-3-phosphate synthase (EPSPS), a target for glyphosate, we found that the position of Pseudanabaena is the closest to plant, which was sensitive to glyphosate, thereby explaining the inhibitory effect of Pseudanabaena following glyphosate exposure. The primary degraded metabolites or analogs did not induce cyanobacterial growth, laterally demonstrating that glyphosate was used as a source of phosphorus to accelerate cyanobacterial growth because phosphorus levels increased in the medium of glyphosate treatment. Overall, this study provides a better understanding of the influence of glyphosate on the composition of aquatic microbiota and explains the mechanism of cyanobacterial response to glyphosate.

Effect of glyphosate in Johnsongrass submitted to different soil water potentials

This work aimed to study the efficiency of herbicide glyphosate to control Johnsongrass plants (Sorghum halepense) in different phenological stages of development and when submitted to different types of soil water potentials. The study was conducted in a completely randomized design, with four repetitions. The treatments were arranged in a triple factor scheme 3 × 3 × 2, being: three soil water conditions [no water deficit (-0.03 MPa), intermediate water deficit (-0.07 MPa), and high water deficit (-1.5 MPa)], associated with three doses of glyphosate (0.0, 270.0, and 540.0 g a.e. ha^-1) applied in two phenological stages (4-6 leaves and 1-3 tillers). Visual control evaluations were conducted at 7, 14, 21, and 35 days after the herbicide application. Biometric and morphophysiological parameters were also analyzed. With the increase of water restriction, there was a decrease in Johnsongrass morphophysiological components, such as specific leaf area, stomatal conductance, and the difference between environment and leaf temperature, as well as the accumulation of aerial part and roots dry matter, independently of the phenological stage evaluated. The development stage of Johnsongrass influenced the control provided by glyphosate, independently of the dose used. The different water deficits studied reduced the control of glyphosate in the two Johnsongrass development stages evaluated. Severe water deficits reduced the control of glyphosate in Johnsongrass using the recommended dose. In conditions of moderate water deficit, the control was not affected. Thus, the control with lower doses can be the most affected by water deficit.

Distinct response patterns of plants and soil microorganisms to agronomic practices and seasonal variation in a floodplain ecosystem

Introduction

Climate change and anthropogenic activities are the greatest threats to floodplain ecosystems. A growing body of literature shows that floodplain ecosystems have experienced increased chemical fertilizer and pesticide loads, which will disturb the above and belowground ecosystems. However, we lack knowledge regarding the effects of such human activities on the vegetation and soil microbiomes in these ecosystems.

Methods

In the present study, plant functional traits and Illumina Mi-Seq sequencing were to assess the impact of nitrogen fertilizer and glyphosate addition on the structure and function of the vegetation and soil microbiomes (bacteria, fungi, and protists) in a floodplain ecosystem, and to assess the influence of seasonal variation.

Results

We identified distinct response mechanisms of plant and microbial communities to the addition of nitrogen fertilizer and glyphosate, and seasonal variation. Nitrogen fertilizer and glyphosate significantly affected plant diversity, aboveground and underground biomass, and C and N content and significantly changed the leaf area and plant stature of dominant plants. However, the addition of nitrogen fertilizer and glyphosate did not significantly affect the diversity and structure of bacterial, fungal, and protist communities. The application of nitrogen fertilizer could improve the negative effects of glyphosate on the functional traits of plant communities. The seasonal variation of floodplain has significantly changed the soil's physical, chemical, and biological properties. Our results showed that compared with that in summer, the soil ecosystem multifunctionality of the floodplain ecosystem in autumn was significantly lower. Seasonal variation had a significant effect on plant diversity and functional traits. Moreover, seasonal variation significantly affected the community compositions, diversity, and structure of bacteria, fungi, and protists. Seasonal variation had a stronger impact on fungal community assembly than on that of bacteria and protists. In summer, the assembly of the fungal community was dominated by a deterministic process, while in autumn, it is dominated by a stochastic process. In addition, the negative association among bacteria, fungi, and protists has been strengthened in autumn and formed a more robust network to cope with external changes.

Discussion

These results extended our understanding of the ecological patterns of soil microbiomes in floodplain ecosystems and provided support for enhancing the ecological barrier function and the service potential of floodplain ecosystems.

Presence and distribution of triazine herbicides and their effects on microbial communities in the Laizhou Bay, Northern China

This study investigated the distribution of triazine herbicides in the Laizhou Bay, China and found that the total concentrations of triazine herbicides in the seawater and sediments were 111.15-234.85 ng/L and 0.902-4.661 μg/kg, respectively. Triazine herbicides especially ametryn, atrazine, and simazine were negatively correlated with prokaryote diversity in the seawater. While ametryn, desethylatrazine and desisopropylatrazine had positively significant effects on eukaryotes Dinophyceae, Bacillariophyta, and Cercozoa in the sediments. Moreover, the degree of fragmentation of eukaryotic networks increased dramatically with the increasing numbers of removed nodes, but prokaryotic networks did not change with the decrease of nodes. In addition, the stability analysis and neutral community models revealed that eukaryotes were more sensitive to triazine herbicides than prokaryotes. These results suggest that triazine herbicides might affect the structure and interactions of microbial communities. Therefore, more attentions should be paid to the ecological risk of triazine herbicides in marine ecosystems.

Synergy between microalgae and microbiome in polluted waters

Microalga-microbiome interactions are central to both health and disease of aquatic environments. Despite impressive advances in deciphering how microorganisms participate in and impact aquatic ecosystems, the evolution and ecological involvement of microalgae and the microbiome in polluted waters are typically studied independently. Here, the phycosphere (i.e., the consortia of microalgae and the related microbiome) is regarded as an independent and integrated life form, and we summarize the survival strategies exhibited by this symbiont when exposed to anthropogenic pollution. We highlight the cellular strategies and discuss the modulation at the transcriptional and population levels, which reciprocally alters community structure or genome composition for medium-term acclimation or long-term adaptation. We propose a 'PollutantBiome' concept to help the understanding of microalga-microbiome interactions and development of beneficial microbial synthetic communities for pollutant remediation.

Response mechanism of microbial community during anaerobic biotransformation of marine toxin domoic acid

Domoic acid (DA) is a potent neurotoxin produced by toxigenic Pseudo-nitzschia blooms and quickly transfers to the benthic anaerobic environment by marine snow particles. DA anaerobic biotransformation is driven by microbial interactions, in which trace amounts of DA can cause physiological stress in marine microorganisms. However, the underlying response mechanisms of microbial community to DA stress remain unclear. In this study, we utilized an anaerobic marine DA-degrading consortium GLY (using glycine as co-substrate) to systematically investigate the global response mechanisms of microbial community during DA anaerobic biotransformation.16S rRNA gene sequencing and metatranscriptomic analyses were applied to measure microbial community structure, function and metabolic responses. Results showed that DA stress markedly changed the composition of main species, with increased levels of Firmicutes and decreased levels of Proteobacteria, Cyanobacteria, Bacteroidetes and Actinobacteria. Several genera of tolerated bacteria (Bacillus and Solibacillus) were increased, while, Stenotrophomonas, Sphingomonas and Acinetobacter were decreased. Metatranscriptomic analyses indicated that DA stimulated the expression of quorum sensing, extracellular polymeric substance (EPS) production, sporulation, membrane transporters, bacterial chemotaxis, flagellar assembly and ribosome protection in community, promoting bacterial adaptation ability under DA stress. Moreover, amino acid metabolism, carbohydrate metabolism and lipid metabolism were modulated during DA anaerobic biotransformation to reduce metabolic burden, increase metabolic demands for EPS production and DA degradation. This study provides the new insights into response of microbial community to DA stress and its potential impact on benthic microorganisms in marine environments.

The Effects of Roundup™ on Benthic Microbial Assemblages

Given the wide usage of Roundup, a common herbicide, the impacts of its presence in ecological communities are of great interest. Many studies have investigated the effects of glyphosate, the active ingredient in Roundup, on different factions of an ecosystem including on animals, plants, microorganisms, and nutrients. The current study expanded upon these works using Roundup instead of glyphosate to provide a realistic application in which to observe the development of microbial assemblages and nutrient composition in two different habitats. Winogradsky columns were prepared using benthic material from a ditch and a pond. Varying concentrations of Roundup were introduced to the columns at the beginning of the study and microbial growth and nutrient compositions from each column were measured weekly. The results indicate that the presence of Roundup has varying effects on microorganisms and nutrients. While photosynthetic microbes were negatively impacted, a shift in the microbial composition to heterotrophic microbes indicates that these microorganisms were able to utilize some ingredients in Roundup as a nutrient source. Additionally, the temporal analysis of nutrient compositions indicated that microbes metabolize glyphosate starting with the phosphate moiety even when the other compounds in Roundup are present. While these trends were observed in both benthic habitats, the composition of the ecological community can affect its ability to utilize the ingredients in Roundup as a nutrient source.

Glyphosate and glyphosate-based herbicides (GBHs) induce phenotypic imipenem resistance in Pseudomonas aeruginosa

GBHs are the most widely used herbicides for weed control worldwide that potentially affect microorganisms, but the role of their sublethal exposure in the development of antibiotic resistance of Pseudomonas aeruginosa is still not fully investigated. Here, the effects of glyphosate acid (GLY), five glyphosate-based herbicides (GBHs), and POE(15), a formerly used co-formulant, on susceptibility to imipenem, a potent carbapenem-type antibiotic, in one clinical and four non-clinical environmental P. aeruginosa isolates were studied. Both pre-exposure in broth culture and co-exposure in solid media of the examined P. aeruginosa strains with 0.5% GBHs resulted in a decreased susceptibility to imipenem, while other carbapenems (doripenem and meropenem) retained their effectiveness. Additionally, the microdilution chequerboard method was used to examine additive/antagonistic/synergistic effects between GLY/POE(15)/GBHs and imipenem by determining the fractional inhibitory concentration (FIC) indexes. Based on the FIC index values, glyphosate acid and Total demonstrated a potent antagonistic effect in all P. aeruginosa strains. Dominator Extra 608 SL and Fozat 480 reduced the activity of imipenem in only one strain (ATCC10145), while POE(15) and three other GBHs did not have any effect on susceptibility to imipenem. Considering the simultaneous presence of GBHs and imipenem in various environmental niches, the detected interactions between these chemicals may affect microbial communities. The mechanisms of the glyphosate and GBH-induced imipenem resistance in P. aeruginosa are yet to be investigated.

Improvement of aquaculture water quality by mixed Bacillus and its effects on microbial community structure

Microbial remediation, especially the application of probiotics, has recently gained popularity in improving water quality and maintaining aquatic animal health. The efficacy and mechanism of mixed Bacillus for improvement of water quality and its effects on aquatic microbial community structure remain unknown. To elucidate these issues, we applied two groups of mixed Bacillus (Bacillus megaterium and Bacillus subtilis (A0 + BS) and Bacillus megaterium and Bacillus coagulans (A0 + BC)) to the aquaculture system of Crucian carp. Our results showed that the improvement effect of mixed Bacillus A0 + BS on water quality was better than that of A0 + BC, and the NH₄⁺-N, NO₂^--N, NO₃^--N, and total phosphorus (TP) concentrations were reduced by 46.3%, 76.3%, 35.6%, and 80.3%, respectively. In addition, both groups of mixed Bacillus increased the diversity of the bacterial community and decreased the diversity of the fungal community. Microbial community analysis showed that mixed Bacillus A0 + BS increased the relative abundance of bacteria related with nitrogen and phosphorus removal, such as Proteobacteria, Actinobacteria, Comamonas, and Stenotrophomonas, but decreased the relative abundance of pathogenic bacteria (Acinetobacter and Pseudomonas) and fungi (Epicoccum and Fusarium). Redundancy analysis showed that NH₄⁺-N, NO₂^--N, and TP were the primary environmental factors affecting the microbial community in aquaculture water. PICRUST analysis indicated that all functional pathways in the A0 + BS group were richer than those in other groups. These results indicated that mixed Bacillus A0 + BS addition produced good results in reducing nitrogenous and phosphorus compounds and shaped a favorable microbial community structure to further improve water quality.

Heat waves rather than continuous warming exacerbate impacts of nutrient loading and herbicides on aquatic ecosystems

Submerged macrophytes are vital components in shallow aquatic ecosystems, but their abundances have declined globally. Shading by periphyton and phytoplankton/turbidity plays a major role in this decline, and the competing aquatic primary producers are subject to the complex influence of multiple stressors such as increasing temperatures, nutrient loading and herbicides. Their joint impact has rarely been tested and is difficult to predict due to potentially opposing effects on the different primary producers, their interactions and their grazers. Here, we used 48 mesocosms (2500 L) to simulate shallow lakes dominated by two typical submerged macrophytes, bottom-dwelling Vallisneria denseserrulata and canopy-forming Hydrilla verticillata, and associated food web components. We applied a combination of nutrient loading, continuous warming, heat waves and glyphosate-based herbicides to test how these stressors interactively impact the growth of submerged macrophytes, phytoplankton and periphyton as competing primary producers. Warming or heat waves alone did not affect phytoplankton and periphyton abundance, but negatively influenced the biomass of V. denseserrulata. Nutrient loading alone increased phytoplankton biomass and water turbidity and thus negatively affected submerged macrophyte biomass, particularly for V. denseserrulata, by shading. Glyphosate alone did not affect biomass of each primary producer under ambient temperatures. However, heat waves facilitated phytoplankton growth under combined nutrient loading and glyphosate treatments more than continuous warming. As a consequence, H. verticillata biomass was lowest under these conditions indicating the potential of multiple stressors for macrophyte decline. Our study demonstrated that multiple stressors interactively alter the biomass of primary producers and their interactions and can eventually lead to a loss of macrophyte communities and shift to phytoplankton dominance. These results show the risks in shallow lakes and ponds in agricultural landscapes and underline the need for multiple stressor studies as a base for their future management.

Evaluation of phoxim toxicity on aquatic and zebrafish intestinal microbiota by metagenomics and 16S rRNA gene sequencing analysis

Phoxim is one of the main organophosphorus pesticides used in agricultural production. However, little information is known about how it affects the aquatic microbial community and the intestinal microbiota of fish. Herein, we utilized shotgun metagenomics and 16S rRNA gene sequencing to reveal the aquatic eco-risk of phoxim. Seven days of phoxim exposure significantly changed the composition of aquatic microbial community, obliterated the interactions between microorganisms, and thus reduced the complexity and stability of the microbial community. During long-time exposure (i.e., 14 days), most of the ecological functions were restored due to the redundancy of the microbial community. However, phoxim exposure promoted the dissemination of elfamycin resistance gene. The zebrafish gut microbial community also recovered from a temporary ecological disorder of aquatic microbiota, but phoxim continually affected zebrafish growth and swimming behavior. Overall, our results demonstrated that phoxim exposure significantly changed the structure and function of the microbial community and displayed a negative impact on freshwater ecosystems in a short exposure time.

Xenobiotic pollution affects transcription of antibiotic resistance and virulence factors in aquatic microcosms

Antibiotic resistance genes (ARGs) and virulence factors (VFs) are critical threats to human health. Their abundance in aquatic ecosystems is maintained and enhanced via selection driven by environmental xenobiotics. However, their activity and expression in these environments under xenobiotic stress remains unknown. Here ARG and VF expression profiles were examined in aquatic microcosms under ciprofloxacin, glyphosate and sertraline hydrochloride treatment. Ciprofloxacin increased total expression of ARGs, particularly multidrug resistance genes. Total expression of ARGs and VFs decreased significantly under glyphosate and sertraline treatments. However, in opportunistic human pathogens, these agents increased expression of both ARGs and VFs. Xenobiotic pollutants, such as the compounds we tested here, have the potential to disrupt microbial ecology, promote resistance, and increase risk to human health. This study systematically evaluated the effects of environmental xenobiotics on transcription of ARGs and VFs, both of which have direct relevance to human health. Transcription of such genes has been overlooked in previous studies.

TiO2 nanoparticles exert an adverse effect on aquatic microbial communities

Titanium dioxide nanoparticle (n-TiO₂) is a widely used nanomaterial, which is inevitably released as a residue into aquatic ecosystems during material production and usage. However, the effects of n-TiO₂ on aquatic microbial communities have not been completely elucidated. This study examined the toxic effects of n-TiO₂ on eukaryotic and prokaryotic microbial communities in freshwater environments. We determined that n-TiO₂ had a greater inhibitory effect on the growth of eukaryotic algae than cyanobacteria in monocultures. A similar phenomenon was observed in a microcosm experiment, revealing that n-TiO₂ slightly reduced the content of chlorophyll-a but evidently increased the phycocyanin content. Moreover, the alpha diversity of the eukaryotic community was not affected, whereas its beta diversity increased with exposure to n-TiO₂. Although n-TiO₂ altered the composition of freshwater microbial communities, it did not change the functions of the prokaryotic community, which might be attributed to the functional redundancy of microbiota. Co-occurrence network analysis indicated that n-TiO₂ destabilized the freshwater community, especially the eukaryotic community, and potentially disturbed the aquatic ecosystem. Our study revealed that the ecological risk of n-TiO₂ on aquatic microbial communities is complex; hence, rational utilization of n-TiO₂ should be emphasized.

Derivation of water quality criteria for glyphosate and its formulations to protect aquatic life in China

Extensive use of the herbicide glyphosate leads to a high detection rate in the environment and potential risks to nontarget aquatic life. China ranks first globally in the production and consumption of glyphosate, but there are no glyphosate water quality criteria (WQCs) for protecting aquatic life. Here, data on the acute and chronic toxicity of glyphosate and glyphosate-based formulations (GBFs) to freshwater aquatic life were collected and screened. Significant differences in species sensitivity distributions (SSDs) and toxicity values for acute or chronic toxicity were found between glyphosate and GBFs. The hazardous concentrations for 5% of species (HC₅) of glyphosate or GBFs between native and nonnative species were different, and native species were found to be more sensitive to the toxicity of glyphosate. The acute and chronic WQCs derived with the SSD method for glyphosate based on the toxicity data for native species in China were 3.35 and 0.26 mg/L, respectively, and those found for GBFs were 0.21 and 0.005 mg/L, respectively. The WQCs in this study were quite different from those estimated using similar statistical extrapolation methods in other countries, which reflects the differences in species sensitivity to glyphosate toxicity in different regions. The hazard quotients (HQs) were calculated based on the WQCs and concentrations of glyphosate in some surface waters in China and indicated that glyphosate exhibits medium or high hazard risk in some samples of Tai Lake, surface water in Guiyang, fishpond water in Chongqing, rural drinking water, and surface water and reservoir water in Henan Province. The WQCs of glyphosate and GBFs have scientific significance for the exposure and pollution control of herbicide formulations and the protection of aquatic life in China.

Physiological and Metabolic Response of Arthrospira maxima to Organophosphates

The Spirulina spp. exhibited an ability to tolerate the organophosphates. This study aimed to explore the effects of the herbicide glyphosate on a selected strain of the cyanobacteria Arthrospira maxima cultivated in a company. Experimental cultivations acclimated in aquaria were treated with 0.2 mM glyphosate [N-(phosphonomethyl) glycine]. The culture biomass, the phycocyanin, and the chlorophyll a concentrations were evaluated every week during 42 days of treatment. The differentially expressed proteins in the treated cyanobacteria versus the control cultivations were evaluated weekly during 21 days of treatment. Even if the glyphosate treatment negatively affected the biomass and the photosynthetic pigments, it induced resistance in the survival A. maxima population. Proteins belonging to the response to osmotic stress and methylation pathways were strongly accumulated in treated cultivation; the response to toxic substances and the negative regulation of transcription seemed to have a role in the resistance. The glyphosate-affected enzyme, chorismate synthase, a key enzyme in the shikimic acid pathway, was accumulated during treatment, suggesting that the surviving strain of A. maxima expressed a glyphosate-resistant target enzyme.

Metagenomic ecotoxicity assessment of trace difenoconazole on freshwater microbial community

Difenoconazole, a typical triazole fungicide, inhibits the activity of cytochrome P450 enzyme in fungi, and is extensively used in protecting fruits, vegetables, and cereal crops. However, reports elucidating the effects of difenoconazole on aquatic microbial communities are limited. Our study showed that difenoconazole promoted microalgae growth at concentrations ranging from 0.1 to 5 μg/L, which was similar with its environmental residual concentrations. Metagenomic analysis revealed that the aquatic microbial structure could self-regulate to cope with difenoconazole-induced stress by accumulating bacteria exhibiting pollutant degrading abilities. In the short-term, several functional pathways related to xenobiotic biodegradation and analysis were upregulated to provide ability for aquatic microbial community to process xenobiotic stress. Moreover, most disturbed ecological functions were recovered due to the redundancy of microbial communities after prolonged exposure. Furthermore, the risks associated with the dissemination of antibiotic resistance genes were enhanced by difenoconazole in the short-term. Overall, our study contributes to a comprehensive understanding of the difenoconazole-induced ecological impacts and the behavior of aquatic microbial communities that are coping with xenobiotic stress.

Phyllosphere Microorganisms: Sources, Drivers, and Their Interactions with Plant Hosts

The leaves of plants are colonized by various microorganisms. In comparison to the rhizosphere, less is known about the characteristics and ecological functions of phyllosphere microorganisms. Phyllosphere microorganisms mainly originate from soil, air, and seeds. The composition of phyllosphere microorganisms is mainly affected by ecological and abiotic factors. Phyllosphere microorganisms execute multiple ecological functions by influencing leaf functions and longevity, seed mass, fruit development, and homeostasis of host growth. A plant can respond to phyllosphere microorganisms by secondary metabolite secretion and its immune system. Meanwhile, phyllosphere microorganisms play an important role in ecological stability and environmental safety assessment. However, as a result of the instability of the phyllosphere environment and the poor cultivability of phyllosphere microorganisms in the current research, there are still many limitations, such as the lack of insight into the mechanisms of plant-microorganism interactions, the roles of phyllosphere microorganisms in plant growth processes, the responses of phyllosphere microorganisms to plant metabolites, etc. This review summarizes the latest progress made in the research of the phyllosphere in recent years. This is beneficial for deepening our understanding of phyllosphere microorganisms and promoting the research of plant-atmosphere interactions, plant pathogens, and plant biological control.

A Glyphosate-Based Herbicide Cross-Selects for Antibiotic Resistance Genes in Bacterioplankton Communities

Agrochemicals often contaminate freshwater bodies, affecting microbial communities that underlie aquatic food webs. For example, the herbicide glyphosate has the potential to indirectly select for antibiotic-resistant bacteria. Such cross-selection could occur if the same genes (encoding efflux pumps, for example) confer resistance to both glyphosate and antibiotics. To test for cross-resistance in natural aquatic bacterial communities, we added a glyphosate-based herbicide (GBH) to 1,000-liter mesocosms filled with water from a pristine lake. Over 57 days, we tracked changes in bacterial communities with shotgun metagenomic sequencing and annotated metagenome-assembled genomes (MAGs) for the presence of known antibiotic resistance genes (ARGs), plasmids, and resistance mutations in the enzyme targeted by glyphosate (enolpyruvyl-shikimate-3-phosphate synthase; EPSPS). We found that high doses of GBH significantly increased ARG frequency and selected for multidrug efflux pumps in particular. The relative abundance of MAGs after a high dose of GBH was predictable based on the number of ARGs in their genomes (17% of variation explained) and, to a lesser extent, by resistance mutations in EPSPS. Together, these results indicate that GBHs can cross-select for antibiotic resistance in natural freshwater bacteria. IMPORTANCE Glyphosate-based herbicides (GBHs) such as Roundup formulations may have the unintended consequence of selecting for antibiotic resistance genes (ARGs), as demonstrated in previous experiments. However, the effects of GBHs on ARGs remain unknown in natural aquatic communities, which are often contaminated with pesticides from agricultural runoff. Moreover, the resistance provided by ARGs compared to canonical mutations in the glyphosate target enzyme, EPSPS, remains unclear. Here, we performed a freshwater mesocosm experiment showing that a GBH strongly selects for ARGs, particularly multidrug efflux pumps. These selective effects were evident after just a few days, and the ability of bacteria to survive and thrive after GBH stress was predictable by the number of ARGs in their genomes and, to a lesser extent, by mutations in EPSPS. Intensive GBH application may therefore have the unintended consequence of selecting for ARGs in natural freshwater communities.

Obesity influences composition of salivary and fecal microbiota and impacts the interactions between bacterial taxa

Obesity is an increasing global health concern and is associated with a broad range of morbidities. The gut microbiota are increasingly recognized as important contributors to obesity and cardiometabolic health. This study aimed to characterize oral and gut microbial communities, and evaluate host: microbiota interactions between clinical obesity classifications. We performed 16S rRNA sequencing on fecal and salivary samples, global metabolomics profiling on plasma and stool samples, and dietary profiling in 135 healthy individuals. We grouped individuals by obesity status, based on body mass index (BMI), including lean (BMI 18-124.9), overweight (BMI 25-29.9), or obese (BMI ≥30). We analyzed differences in microbiome composition, community inter-relationships, and predicted microbial function by obesity status. We found that salivary bacterial communities of lean and obese individuals were compositionally and phylogenetically distinct. An increase in obesity status was positively associated with strong correlations between bacterial taxa, particularly with bacterial groups implicated in metabolic disorders including Fretibacterium, and Tannerella. Consumption of sweeteners, especially xylitol, significantly influenced compositional and phylogenetic diversities of salivary and fecal bacterial communities. In addition, obesity groups exhibited differences in predicted bacterial metabolic activity, which was correlated with host's metabolite concentrations. Overall, obesity was associated with distinct changes in bacterial community dynamics, particularly in saliva. Consideration of microbiome community structure and inclusion of salivary samples may improve our ability to understand pathways linking microbiota to obesity and cardiometabolic disease.

Long-term exposure to polyethylene microplastics and glyphosate interferes with the behavior, intestinal microbial homeostasis, and metabolites of the common carp (Cyprinus carpio L.)

Polyethylene microplastics (PE-MPs) and glyphosate (GLY) occur widely and have toxic characteristics, resulting in increased research interest. In this study, common carp were used to assess the individual and combined toxicity of PE-MPs (0, 1.5, or 4.5 mg/L) and GLY (0, 5, or 15 mg/L) on the brain-gut axis. After 60 days of exposure, the developmental toxicity, blood-brain barrier (BBB), locomotor behavior, intestinal barrier (physical barrier, chemical barrier, microbial barrier), and intestinal content metabolism of common carp were evaluated. Results showed that 15 mg/L of GLY exposure significantly reduced the mRNA expression of tight-junction genes (occludin, claudin-2, and ZO-1) in the brain, and acetylcholinesterase (AChE) activity was clearly inhibited by high concentrations of GLY. However, different concentrations of PE-MPs had no significant effect on the activity of AChE. Furthermore, the free-swimming behavior of common carp was distinctly inhibited by treatment with a combination of 15 mg/L GLY and 4.5 mg/L PE-MPs. Histological studies indicated that PE-MPs alone and in combination with GLY could disrupt the physical and chemical intestinal barriers of common carp. Additionally, the abundance and diversity of gut microbiota in common carp were significantly changed when exposed to a combination of PE-MPs and GLY. Metabolomics further revealed that PE-MPs combined with GLY triggered metabolic changes and that differential metabolites were related to amino acid and lipid metabolism. These findings illustrate that exposure to PE-MPs or GLY alone is toxic to fish and results in physiological changes to the brain-gut axis. This work offers a robust analysis to understand the mechanisms underlying GLY and MP-induced aquatic toxicity.

Effects of Imazethapyr on Soybean Root Growth and Soil Microbial Communities in Sloped Fields

The herbicide imazethapyr was previously recommended for controlling weeds in soybean fields. However, the effects of imazethapyr on soil microbial communities and their relationship with crop root growth in sloped soils remain unclear. In this study, a field experiment was conducted on a sloped field to explore the effects of imazethapyr on crop root growth, microbial communities, microbial co-occurrence networks, and the interactions between microbes and crop root growth. The field experiment included two factors: slope and imazethapyr. The slope factor included three different slope gradients: 5° (S1), 10° (S2), and 15° (S3). The imazethapyr factor included two treatments: with (I1) and without (I0) imazethapyr. Thus, six total combinations of slope and imazethapyr treatments were tested in this study: S1I1, S2I1, S3I1, S1I0, S2I0, and S3I0. The results show that, compared to the I0 treatments, the I1 treatments significantly increased the soybean root length, surface area, and volume by 11.7~26.5 m, 171.7~324.2 cm2, and 1.8~3.1 cm3, respectively, across all the slopes. The Proteobacteria, Actinobacteriota, and Bacteroidota bacterial phyla and Ascomycota and Basidiomycota fungal phyla were found to be the top phyla represented bacterial and fungal communities. These five phyla were scattered in co-occurrence networks of bacterial and fungal communities, suggesting these phyla play critical roles in enhancing the stability of co-occurrence networks. Compared to the I0 treatments, the I1 treatments increased nodes from Proteobacteria, Actinobacteriota, and Bacteroidota phyla by 6.4%, 9.1%, and 11.2%, respectively, in the bacterial co-occurrence network. Similarly, in the fungal co-occurrence network, the I1 treatments improved nodes from Ascomycota and Basidiomycota phyla by 1.8% and 5.8%, respectively. Compared to the I0 treatments, the I1 treatments increased positive relations by 8.3% and 3.2%, respectively, in the bacterial and fungal co-occurrence networks. Moreover, the I1 treatments increased the relative abundance of root-promoting biomarkers and suppressed root-limiting biomarkers. However, the application of imazethapyr reduced the diversity and richness of bacterial and fungal communities in general. Furthermore, the nodes and links of bacterial co-occurrence networks in the I0 treatments were 9.2% and 78.8% higher than these in the I1 treatments. Similarly, the I1 treatments also decreased 17.9% of fungal community links compared to the I0 treatments. Our data also show that compared to the I0 treatments, the I1 treatments decreased almost all gene families encoding nitrogen and carbon cycling pathways. In conclusion, the application of imazethapyr increased soybean root growth by increasing root-promoting biomarkers and improved the stability and cooperation of co-occurrence networks of bacterial and fungal communities. However, the application of imazethapyr had some negative impacts on microbial communities, such as reducing the diversity of bacterial and fungal communities and nitrogen and carbon cycling pathways.

Effects of ofloxacin on the structure and function of freshwater microbial communities

Ofloxacin (OFL) is a broad-spectrum fluoroquinolone antibiotic frequently used in clinic for treating bacterial infections. The discharged OFL would inevitably enter into aquatic ecosystems, affecting the growth of non-target microorganisms, which may result in micro-ecosystem imbalance. To the best of our knowledge, researches in this area are rather sparse. The present study evaluated the response of photosynthetic microorganisms (cyanobacteria, eukaryotic algae) and aquatic microbial community to OFL in a microcosm. Results showed that ofloxacin presented an inhibitory effect on the growth Microcystis aeruginosa. Although 0.1 mg/L OFL has no significant impact on alpha diversity of the microbial communities, it obviously altered the structure and decreased the species interaction of prokaryotic community by reducing the capacities of nitrogen fixation, photosynthetic and metabolic capacity of the microbial community. This study pointed out that the residual OFL in water would disturb the balance of the aquatic micro-ecology, suggesting that more attentions should be given to the negative effects of antibiotics and other bioactive pollutants on aquatic environments.

New Methods for Testing/Determining the Environmental Exposure to Glyphosate in Sunflower (Helianthus annuus L.) Plants

Glyphosate is still the subject of much debate, as several studies report its effects on the environment. Sunflower (GK Milia CL) was set up as an experimental plant and treated with glyphosate concentrations of 500 ppm and 1000 ppm in two treatments. Glyphosate was found to be absorbed from the soil into the plant organism through the roots, which was also detectable in the leaf and root. Glyphosate was also significantly detected in the plant 5 weeks after treatment and in plants that did not receive glyphosate treatment directly, so it could be taken up through the soil. Based on the morphological results, treatment with higher concentrations (1000 ppm) of glyphosate increased the dried mass and resulted in shorter, thicker roots. Histological results also showed that basal and transporter tissue distortions were observed in the glyphosate-treated plants compared to the control group. Cells were distorted with increasing concentration, vacuoles formed, and the cell wall was weakened in both the leaf-treated and inter-row-treated groups. In the future, it will be worth exploring alternative agricultural technologies that can reduce the risk of glyphosate while increasing economic outcomes. This may make the use of glyphosate more environmentally conscious.

Rethinking the term "glyphosate effect" through the evaluation of different glyphosate-based herbicide effects over aquatic microbial communities

Glyphosate-based herbicides (GBH) -the most widely used herbicides in agriculture worldwide-are frequently generalized by the name of "glyphosate". However, GBH encompass a variety of glyphosate salts as active ingredient and different adjuvants, which differ between products. These herbicides reach water bodies and produce diverse impacts over aquatic communities. Yet, the risk assessment assays required for the approval focus mostly on active ingredients. Herein, we compared the effect of five different GBH as well as of monoisopropylamine salt of glyphosate (GIPA) on aquatic microbial communities from natural shallow lakes that were mixed and allowed to evolve in an outdoor pond. We performed an 8-day long assay under indoor control conditions to evaluate the effects of exposure on the structure of nano-plus microphytoplankton (net phytoplankton, with sizes between 2 and 20 μm and >20 μm, respectively) and picoplankton (size ranging between 0.2 and 2 μm) communities through microscopy and flow cytometry, respectively. Significantly different effects were evident on the structure of microbial communities dependent on the GBH, even with herbicides sharing similar active ingredients. Each GBH evoked increases of different magnitude in bacterioplankton abundance. Furthermore, GIPA and a formulation decreased the abundance of a phycocyanin-rich (PC-rich) picocyanobacteria (Pcy) cytometric population and GIPA further altered Pcy composition. Also, two GBH increased net phytoplankton total abundance and, unlike the tested GBH, no apparent effect of GIPA was detected on this community structure. These results demonstrate that GBH effects on aquatic microbial communities should not be summarized as "glyphosate" effects considering that the formulations have effects beyond those exerted by the active ingredients alone. This work intends to alert on the lack of real knowledge regarding the consequences of the variety of GBH on natural aquatic ecosystems. Indeed, the wide use of the term "glyphosate effect" should be thoroughly rethought.

Synergetic toxicity of silver nanoparticle and glyphosate on wheat (Triticum aestivum L.)

Silver nanoparticles (AgNPs) are one of the most commonly used nanomaterials in industrial and agricultural production. Glyphosate is a broad-spectrum systemic herbicide, which mainly acts in the phloem of weeds that compete with crop growth and is widely used in agriculture. This study investigated the interactive effects of AgNPs and glyphosate on the physiological morphology, gene transcription, and rhizosphere microorganisms of wheat. Our results demonstrated that wheat growth, and the structure and diversity of rhizosphere microorganisms were slightly influenced by AgNPs and glyphosate single treatment at the test concentration. However, AgNPs and glyphosate (Gly) combined treatment (AgNPs + Gly) strongly inhibited wheat growth and influenced gene transcription. In total, 955, 601, and 1336 genes were determined to be differentially expressed in AgNPs, glyphosate, and combined treatment, respectively. According to KEGG analysis, the combined groups induced an antioxidant response by upregulating the transcription of phenylpropanoid biosynthesis-related genes. In addition, more energy was needed, and disrupted cell membrane was shown in the combined treatment, which displayed in the upregulation of sucrose, starch, and lipid synthesis. Moreover, the relative abundance of Bradyrhizobium, Devosia, Kribbella, Sphingopyxis (nitrogen-fixing bacteria), and Streptomyces (plant growth-promoting bacteria) in soil microbiota were decreased, implicated that nitrogen fixation and some beneficial substance secretions were inhibited by the combined treatment. This study emphasized that the synergetic effects of AgNPs and glyphosate exerted a negative impact on wheat growth.

Detection of the maximum resistance to the herbicides diuron and glyphosate, and evaluation of its phenotypic cost, in freshwater phytoplankton

One of the most important anthropogenic impacts on freshwater aquatic ecosystems close to intensive agriculture areas is the cumulative increase in herbicide concentrations. The threat is especially relevant for phytoplankton organisms because they have the same physiological targets as the plants for which herbicides have been designed. This led us to explore the evolutionary response of three phytoplanktonic species to increasing concentrations of two herbicides and its consequences in terms of growth and photosynthesis performance. Specifically, we used an experimental ratchet protocol to investigate the differential evolution and the limit of resistance of a cyanobacterium (Microcystis aeruginosa) and two chlorophyceans (Chlamydomonas reinhardtii and Dictyosphaerium chlorelloides) to two herbicides in worldwide use: glyphosate and diuron. Initially, the growth rate of M. aeruginosa and D. chlorelloides was completely inhibited when they were exposed to a dose of 0.23 ppm diuron or 40 ppm glyphosate, whereas a higher concentration of both herbicides (0.46 ppm diuron or 90 ppm glyphosate) was necessary to abolish C. reinhardtii growth. However, after running a ratchet protocol, the resistance of the three species to both herbicides increased by an adaptation process. M. aeruginosa and D. chlorelloides were able to grow at 1.84 ppm diuron and 80 ppm glyphosate and C. reinhardtii proliferated at twice these concentrations. Herbicide-resistant strains showed lower growth rates than their wild-type counterparts in the absence of herbicides, as well as changes on morphology and differences on photosynthetic pigment content. Besides, herbicide-resistant cells generally showed a lower photosynthetic performance than wild-type strains in the three species. These results indicate that the introduction of both herbicides in freshwater ecosystems could produce a diminution of primary production due to the selection of herbicide-resistant mutants, that would exhibit lower photosynthetic performance than wild-type populations.

Widespread agrochemicals differentially affect zooplankton biomass and community structure

Anthropogenic environmental change is causing habitat deterioration at unprecedented rates in freshwater ecosystems. Despite increasing more rapidly than many other agents of global change, synthetic chemical pollution-including agrochemicals such as pesticides-has received relatively little attention in freshwater community and ecosystem ecology. Determining the combined effects of multiple agrochemicals on complex biological systems remains a major challenge, requiring a cross-field integration of ecology and ecotoxicology. Using a large-scale array of experimental ponds, we investigated the response of zooplankton community properties (biomass, composition, and diversity metrics) to the individual and joint presence of three globally widespread agrochemicals: the herbicide glyphosate, the neonicotinoid insecticide imidacloprid, and nutrient fertilizers. We tracked temporal variation in zooplankton biomass and community structure along single and combined pesticide gradients (each spanning eight levels), under low (mesotrophic) and high (eutrophic) nutrient-enriched conditions, and quantified (1) response threshold concentrations, (2) agrochemical interactions, and (3) community resistance and recovery. We found that the biomass of major zooplankton groups differed in their sensitivity to pesticides: ≥0.3 mg/L glyphosate elicited long-lasting declines in rotifer communities, both pesticides impaired copepods (≥3 µg/L imidacloprid and ≥5.5 mg/L glyphosate), whereas some cladocerans were highly tolerant to pesticide contamination. Strong interactive effects of pesticides were only recorded in ponds treated with the combination of the highest doses. Overall, glyphosate was the most influential driver of aggregate community properties of zooplankton, with biomass and community structure responding rapidly but recovering unequally over time. Total community biomass showed little resistance when first exposed to glyphosate, but rapidly recovered and even increased with glyphosate concentration over time; in contrast, taxon richness decreased in more contaminated ponds but failed to recover. Our results indicate that the biomass of tolerant taxa compensated for the loss of sensitive species after the first exposure, conferring greater community resistance upon a subsequent contamination event; a case of pollution-induced community tolerance in freshwater animals. These findings suggest that zooplankton biomass may be more resilient to agrochemical pollution than community structure; yet all community properties measured in this study were affected at glyphosate concentrations below common water quality guidelines in North America.

Nano-Sized Polystyrene at 1 mg/L Concentrations Does Not Show Strong Disturbance on the Freshwater Microbial Community

In recent years, microplastics and nanoplastics have gained public attention, but their impacts on the freshwater microbial communities is rarely evaluated. In this study, the effects of 1 mg/L nano-sized polystyrene (nPS) and its modified forms (carboxyl-modified and amino-modified nPS) on the structures and functions of freshwater microbial community were determined. The nPS were found to slightly reduce the chlorophyll-a and increase the phycocyanin contents of freshwater microbial communities. Moreover, the richness of the microbial communities temporarily decreased during this process, while their diversity remained uninfluenced by treatment with nPS. Although the three tested nPS types were found to disturb the compositions of both the prokaryotic and eukaryotic communities to some degree, they did not affect the functions of freshwater bacterial communities significantly due to functional redundancy. Our study demonstrated that the ecotoxicities of the nPS itself were found to be lower than what is generally expected.

Ecotoxicological QSAR modeling of the acute toxicity of organic compounds to the freshwater crustacean Thamnocephalus platyurus

Growing interest in environmental toxicity assessment using Thamnocephalus platyurus as organism has led to an increased availability of acute toxicity data. Despite this growing interest in tests with this organism, however, to the best of our knowledge there are no computational models to predict the acute toxicity in T. platyurus. In view of the limited number of in silico models for this crustacean, we developed Quantitative Structure-Activity Relationship (QSAR) models for the prediction of acute toxicity towards T. platyurus, reflected by the 24h LC_50, using publicly available data according to the ISO 14380:2011 guideline. Two models were developed following the principles of QSAR modeling recommended by the Organization for Economic Cooperation and Development (OECD). We used partial least squares and gradient boosting machine techniques, which gave encouraging statistical quality in our data set.

Meta-transcriptomic profiling of functional variation of freshwater microbial communities induced by an antidepressant sertraline hydrochloride

Sertraline hydrochloride (Ser-HCl) is an effective and commonly used antidepressant drug, which is also frequently detected in aquatic environments. Our previous research showed that Ser-HCl changes the community composition of aquatic microbiome, but the understanding of the expression of functional pathways in microbial communities is still incomplete; to address this knowledge gap, we used meta-transcriptomics analysis to evaluate the toxicity of Ser-HCl to natural aquatic microbial communities cultured in laboratory microcosms. Meta-transcriptomic results show that a 15-day exposure to 50 μg/L Ser-HCl significantly changed the functional expression activity of aquatic microbial communities. Pathways related to lipid metabolism, energy metabolism, membrane transport function, and genetic information processing in the aquatic microbial community were severely inhibited under Ser-HCl treatment, but metabolism of cofactors and vitamins to alleviate biological toxicity after Ser-HCl exposure was enhanced. Our study thus reveals details of the effects of sertraline on the functioning of aquatic microbiome. Due to the extensive use of Ser-HCl and its strong biological activity, it should not continue to be an overlooked pollutant. Therefore, more attention should be paid to the negative effects of such biologically active drugs on the expression of aquatic microbiome.

Pollutants affect algae-bacteria interactions: A critical review

With increasing concerns on the ecological risks of pollutants, many efforts have been devoted to revealing the toxic effects of pollutants on algae or bacteria in their monocultures. However, how pollutants affect algae and bacteria in their cocultures is still elusive but crucial due to its more environmental relevance. The present review outlines the interactions between algae and bacteria, reveals the influential mechanisms of pollutants (including pesticides, metals, engineered nanomaterials, pharmaceutical and personal care products, and aromatic pollutants) to algae and bacteria in their coexisted systems, and puts forward prospects for further advancing toxic studies in algal-bacterial systems. Pollutants affect the physiological and ecological functions of bacteria and algae by interfering with their relationships. Cell-to-cell adhesion, substrate exchange and biodegradation of organic pollutants, enhancement of signal transduction, and horizontal transfer of tolerance genes are important defense strategies in algal-bacterial systems to cope with pollution stress. Developing suitable algal-bacterial models, identifying cross-kingdom signaling molecules, and deciphering the horizontal transfer of pollutant resistant genes between algae and bacteria under pollution stress are the way forward to fully exploit the risks of pollutants in natural aquatic environments.

Reproductive toxicity of Roundup WG® herbicide: impairments in ovarian follicles of model organism Danio rerio

Glyphosate-based herbicides are widely used in global agriculture, and their effects on different non-target animal organisms have been the focus of many toxicological studies. Regarding the potential role of glyphosate-based herbicides as an endocrine disruptor, the present study aims to investigate the effects of the herbicide Roundup WG® (RWG) on female reproduction, specifically on the ovarian maturation of Danio rerio. Adult females were exposed to low concentrations of RWG (0.065, 0.65, and 6.5 mg L^-1) for 15 days, and then the ovaries were submitted to structural and morphometric procedures, accompanied by analysis of the vitellin protein content. Our results showed an increase of initial ovarian follicle numbers, decrease of late ovarian follicles, and smaller diameter of ovarian follicles in fish exposed to 0.065 and 6.5 mg L^-1. The thickness of vitelline envelope was reduced, and the vitellin protein content was increased in the ovarian follicle in the two highest concentrations. Ultrastructural changes in the ovarian follicular component were evident and expressed by the cell index; vacuolization in follicular cells, increase of perivitelline space, and impaired mitochondria in oocytes were observed. Therefore, RWG adversely affects the ovarian maturation in D. rerio, and these changes can lead to reproductive toxicity, compromising population dynamics.

Glyphosate Accelerates the Proliferation of Microcystis aeruginosa, a Dominant Species in Cyanobacterial Blooms

Glyphosate is a commonly used herbicide known for its high performance in killing certain plants and grasses; however, its use is regulated due to its harmful effects on the aquatic environment. The present study investigated and compared the toxic mechanisms of glyphosate on Microcystis aeruginosa (a toxin-producing cyanobacterium) under 2 conditions: 0‰ saline media (experiment I) and 2.5‰ saline media (experiment II). The results indicated that an appropriate concentration of glyphosate provided a phosphate source for M. aeruginosa, resulting in an increased specific growth rate in both experimental groups compared with the controls. Glyphosate-enhanced alkaline phosphatase (ALP) activity increased by up to 1.37-fold in experiment I and 1.68-fold in experiment II. Moreover, the activities of superoxide dismutase (SOD) and catalase (CAT) decreased at glyphosate concentrations below 1.2 mg L-1 but increased at concentrations greater than 1.2 mg L-1 in experiment I, whereas SOD and CAT activities decreased in experiment II and declined by 64 and 49% in the 30 mg L-1 treatments. Furthermore, the transcript abundances of the pyruvate carboxylase (pcB), microcystin synthetase B (mcyB), and paired-like homeobox (phoX) genes were up-regulated by up to 6.92-, 3.63-, and 2.27-fold in experiment I and 6.74-, 6.55-, and 4.86-fold in experiment II after 96 h of incubation. The addition of glyphosate stimulated the production of dissolved organic matter including tryptophan-like substances, fulvic acid-like substances, (marine) humic acid-like substances, and microcystin-leucine-arginine in the culture. In conclusion, glyphosate stimulates the proliferation of M. aeruginosa and enhances the release of dissolved organic matter in saltwater ecosystems. Environ Toxicol Chem 2021;40:342-351. © 2020 SETAC.

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.

Ecotoxicology of Glyphosate, Its Formulants, and Environmental Degradation Products

The chemical and biological properties of glyphosate are key to understanding its fate in the environment and potential risks to non-target organisms. Glyphosate is polar and water soluble and therefore does not bioaccumulate, biomagnify, or accumulate to high levels in the environment. It sorbs strongly to particles in soil and sediments and this reduces bioavailability so that exposures to non-target organisms in the environment are acute and decrease with half-lives in the order of hours to a few days. The target site for glyphosate is not known to be expressed in animals, which reduces the probability of toxicity and small risks. Technical glyphosate (acid or salts) is of low to moderate toxicity; however, when mixed with some formulants such as polyoxyethylene amines (POEAs), toxicity to aquatic animals increases about 15-fold on average. However, glyphosate and the formulants have different fates in the environment and they do not necessarily co-occur. Therefore, toxicity tests on formulated products in scenarios where they would not be used are unrealistic and of limited use for assessment of risk. Concentrations of glyphosate in surface water are generally low with minimal risk to aquatic organisms, including plants. Toxicity and risks to non-target terrestrial organisms other than plants treated directly are low and risks to terrestrial invertebrates and microbial processes in soil are very small. Formulations containing POEAs are not labeled for use over water but, because POEA rapidly partitions into sediment, risks to aquatic organisms from accidental over-sprays are reduced in shallow water bodies. We conclude that use of formulations of glyphosate under good agricultural practices presents a de minimis risk of direct and indirect adverse effects in non-target organisms.

Alteration of dominant cyanobacteria in different bloom periods caused by abiotic factors and species interactions

Freshwater cyanobacterial blooms have drawn public attention because they threaten the safety of water resources and human health worldwide. Heavy cyanobacterial blooms outbreak in Lake Taihu in summer annually and vanish in other months. To find out the factors impacting the cyanobacterial blooms, the present study measured the physicochemical parameters of water and investigated the composition of microbial community using the 16S rRNA gene and internal transcribed spacer amplicon sequencing in the months with or without bloom. The most interesting finding is that two major cyanobacteria, Planktothrix and Microcystis, dramatically alternated during a cyanobacterial bloom in 2016, which is less mentioned in previous studies. When the temperature of the water began increasing in July, Planktothrix appeared first and showed as a superior competitor for M. aeruginosa in NO₃^--rich conditions. Microcystis became the dominant genus when the water temperature increased further in August. Laboratory experiments confirmed the influence of temperature and the total dissolved nitrogen (TDN) form on the growth of Planktothrix and Microcystis in a co-culture system. Besides, species interactions between cyanobacteria and non-cyanobacterial microorganisms, especially the prokaryotes, also played a key role in the alteration of Planktothrix and Microcystis. The present study exhibited the alteration of two dominant cyanobacteria in the different bloom periods caused by the temperature, TDN forms as well as the species interactions. These results helped the better understanding of cyanobacterial blooms and the factors which contribute to them.