Influence of Temperature and Nickel on Algal Biofilm Fatty Acid Composition

Metal Mixture Effects of Ni, Cu, and Zn in a Multispecies, Two-Trophic-Level Algal-Daphnid Microcosm Can Be Predicted From Single-Trophic-Level Effects: The Role of Indirect Toxicity

Effect assessments of metals are mostly based on single-metal, single-species tests, thereby ignoring metal-mixture effects and indirect effects through species interactions. We tested the combined effects of metal and species interactions in two-trophic algal-daphnid microcosms. Metal-mixture effects on daphnid communities may propagate from effects on the generally more sensitive algal communities. Four different algal communities (three species each), with and without addition of the same daphnid community (three species) were exposed to single metals and one metal mixture (17:17:51 µg/L Ni:Cu:Zn). Daphnid densities were negatively affected by metals in the two-trophic test, the magnitude of which depended on the algal community composition. Algal densities were overall positively affected by the metals in the two-trophic test but negatively in the single-trophic test, illustrating an indirect positive effect in the two-trophic system due to a reduced grazing pressure. Metal effects on daphnid communities in the two-trophic test (day 21) were correlated with metal effects on the single-trophic-level algal communities during exponential growth (R2 = 0.55, p = 0.0011). This finding suggests that metal effects propagate across trophic levels due to a reduced food quantity. However, the indirect positive effects on algal densities, resulting in abundant food quantity, suggests that metal effects can also propagate to daphnids due to a reduced food quality (not measured directly). Metal-mixture interactions on daphnid densities varied during exposure, but were additive or antagonistic relative to independent action when final daphnid densities were considered (day 56). This suggests stronger indirect effects of the mixture compared with the single metals. Overall, our study highlights the dynamic aspect of community-level effects, which empirical reference models such as independent action or concentration addition cannot predict. Environ Toxicol Chem 2024;00:1-15. © 2024 SETAC.

Temperature influence on the sensitivity of Artemia franciscana to globally used pesticides - Oxyfluorfen and copper

Climate change further the world's human population increase is a mainstream political issue, and it's critical to search for solutions to produce enough food to feed everyone. Pesticides and fertilizers have been used as an easy solution to prevent pests and increase food production. Nevertheless, their overuse has dangerous effects on the ecosystems and communities. Oxyfluorfen (Oxy) and copper (Cu) based formulations are used as pesticides and widely applied on agricultural fields for crop protection. However, they have shown negative effects on non-target species. So, this work proposes to: a)determine the lethal concentration of Oxy and Cu to the zooplankton, Artemia franciscana, at different temperatures (15 °C, 20 °C and 25 °C); b)understand the biochemical impacts of these chemicals at the different temperatures scenarios, on A. franciscana and c)evaluate the impact of the climate changes, particularly the temperature increase, on this species sensitivity to the tested pesticides. Acute and sub-lethal bioassays with Oxy and Cu were performed at different temperatures to determine the lethal concentration of each chemical and to understand the effects of the compounds at different temperatures on the biochemical profiles of A. franciscana. Results showed an increase in chemicals toxicity with the temperature, and Oxy was revealed to be more noxious to A. franciscana than Cu; at a biochemical level, significant differences were observed among temperatures, with the biggest differences between the organisms exposed to 15 °C and 25 °C. Overall, a decrease in fatty acids (FA) and sugars was observed with the increase in Cu and oxyfluorfen concentrations. Different trends were observed with temperature increase, with FA increase in the organisms exposed to Cu and the opposite was observed in the ones exposed to oxyfluorfen. Sugar content decreases in the organisms exposed to oxyfluorfen with temperature increase and showed a non-linear behaviour in the ones exposed to Control and Cu treatments.

The Easily Overlooked Effect of Global Warming: Diffusion of Heavy Metals

Since industrialization, global temperatures have continued to rise. Human activities have resulted in heavy metals being freed from their original, fixed locations. Because of global warming, glaciers are melting, carbon dioxide concentrations are increasing, weather patterns are shifting, and various environmental forces are at play, resulting in the movement of heavy metals and alteration of their forms. In this general context, the impact of heavy metals on ecosystems and organisms has changed accordingly. For most ecosystems, the levels of heavy metals are on the rise, and this rise can have a negative impact on the ecosystem as a whole. Numerous studies have been conducted to analyze the combined impacts of climate change and heavy metals. However, the summary of the current studies is not perfect. Therefore, this review discusses how heavy metals affect ecosystems during the process of climate change from multiple perspectives, providing some references for addressing the impact of climate warming on environmental heavy metals.

Meta-metabolomic responses of river biofilms to cobalt exposure and use of dose-response model trends as an indicator of effects

The response of the meta-metabolome is rarely used to characterize the effects of contaminants on a whole community. Here, the meta-metabolomic fingerprints of biofilms were examined after 1, 3 and 7 days of exposure to five concentrations of cobalt (from background concentration to 1 × 10-5 M) in aquatic microcosms. The untargeted metabolomic data were processed using the DRomics tool to build dose-response models and to calculate benchmark-doses. This approach made it possible to use 100% of the chemical signal instead of being limited to the very few annotated metabolites (7%). These benchmark-doses were further aggregated into an empirical cumulative density function. A trend analysis of the untargeted meta-metabolomic feature dose-response curves after 7 days of exposure suggested the presence of a concentration range inducing defense responses between 1.7 × 10-9 and 2.7 × 10-6 M, and of a concentration range inducing damage responses from 2.7 × 10-6 M and above. This distinction was in good agreement with changes in the other biological parameters studied (biomass and chlorophyll content). This study demonstrated that the molecular defense and damage responses can be related to contaminant concentrations and represents a promising approach for environmental risk assessment of metals.

Effects of atrazine and S-metolachlor on stream periphyton taxonomic and fatty acid compositions

Extensive pesticide use for agriculture can diffusely pollute aquatic ecosystems through leaching and runoff events and has the potential to negatively affect non-target organisms. Atrazine and S-metolachlor are two widely used herbicides often detected in high concentrations in rivers that drain nearby agricultural lands. Previous studies focused on concentration-response exposure of algal monospecific cultures, over a short exposure period, with classical descriptors such as cell density, mortality or photosynthetic efficiency as response variables. In this study, we exposed algal biofilms (periphyton) to a concentration gradient of atrazine and S-metolachlor for 14 days. We focused on fatty acid composition as the main concentration-response descriptor, and we also measured chlorophyll a fluorescence. Results showed that atrazine increased cyanobacteria and diatom chlorophyll a fluorescence. Both herbicides caused dissimilarities in fatty acid profiles between control and high exposure concentrations, but S-metolachlor had a stronger effect than atrazine on the observed increase or reduction in saturated fatty acids (SFAs) and very long-chain fatty acids (VLCFAs), respectively. Our study demonstrates that two commonly used herbicides, atrazine and S-metolachlor, can negatively affect the taxonomic composition and fatty acid profiles of stream periphyton, thereby altering the nutritional quality of this resource for primary consumers.

Characterization of dissolved organic matter content, composition, and source during spring algal bloom in tributaries of the Three Gorges Reservoir

Dissolved organic matter (DOM) is a key component of aquatic ecosystem function and biogeochemical processes. The characteristics of DOM in tributaries of the Three Gorges Reservoir (TGR) during the severe spring algal bloom period and their relationship with algal growth are unclear. In this study, the content, composition, and source of DOM in the Pengxi River (PXR) and Ruxi River (RXR) exhibiting typical TGR bloom problems were analyzed using various physicochemical indexes, carbon isotopes, fatty acids, and metagenomics. The results showed that chlorophyll a content increased with rising DOM concentration in the PXR and RXR. The dissolved organic carbon (DOC) and chromophoric dissolved organic matter (CDOM) contents in the two rivers were 4.656-16.560 mg/L and 14.373-50.848 μg/L, respectively, and increased during the bloom period. Four fluorescent components were identified, namely, two humic-like substances, and two protein-like substances. Proteobacteria, bacteroidetes, and actinobacteria were the greatest contributors to DOM content. The carbon fixation pathway of microorganisms increased the DOC concentration in both rivers during the bloom period. Physicochemical parameters (WT, pH, DO, and PAR) affected the DOM concentration by influencing microbial activity and DOM degradation. DOM in both rivers was derived from allochthonous and autogenous sources. Meanwhile, the DOC content was more strongly correlated with allochthonous sources. These findings might provide essential information for improving water environment management and algal bloom control in the TGR.

Ecotoxicological and biochemical effects of a binary mixture of pesticides on the marine diatom Thalassiosira weissflogii in a scenario of global warming

Under the current scenario of global warming, it is ecologically relevant to understand how increased temperature influences the combined toxicity of pesticides to aquatic species. Hence, this work aims to: a) determine the temperature effect (15 °C, 20 °C and 25 °C) on the toxicity of two pesticides (oxyfluorfen and Copper (Cu)), on the growth of Thalassiosira weissflogii; b) assess whether temperature affects the type of toxicity interaction between these chemicals; and c) assess the temperature effect on biochemical responses (fatty acids (FA) and sugar profiles) of the pesticides on T. weissflogii. Temperature increased the tolerance of the diatoms to the pesticides with EC₅₀ values between 3.176 and 9.929 μg L^-1 for oxyfluorfen and 42.50-230.75 μg L^-1 for Cu, respectively, at 15 °C and 25 °C. The mixtures toxicity was better described by the IA model, but temperature altered the type of deviation from dose ratio (15 °C and 20 °C) to antagonism (25 °C). Temperature, as well as the pesticide concentrations, affected the FA and sugar profiles. Increased temperature increased saturated FA and decreased unsaturated FA; it also affected the sugar profiles with a pronounced minimum at 20 °C. Results highlight effects on the nutritional value of these diatoms, with potential repercussion on food webs.

Metabolites and metabolic pathways associated with allelochemical effects of linoleic acid on Karenia mikimotoi

Linoleic acid (LA) shows great potential in inhibiting the growth of multiple red tide microalgae by disturbing algal physio-biochemical processes. However, our knowledge on the mechanisms of algal mortality at metabolic level remains limited. Herein, the response of K. mikimotoi to LA was evaluated using metabolomics, stable isotope techniques (SIT), and physiological indicators. Results showed that 100 μg/L LA promoted the growth of K. mikimotoi, which was significantly inhibited by 500 μg/L LA, along with a significant reduction of photosynthetic pigments and a significant increase of reactive oxygen species (ROS). SIT showed that LA entered algal cells, and 56 isotopologues involved in ferroptosis, carotenoid biosynthesis, and porphyrin metabolism were identified. Non-targeted metabolomics identified 90 and 111 differential metabolites (DEMs) belonging to 11 metabolic pathways under the 500 μg/L and 100 μg/L LA exposure, respectively. Among them, 34 DEMs were detected by SIT. Metabolic pathway analysis showed that 500 μg/L LA significantly promoted ferroptosis, and significantly inhibited carotenoid biosynthesis, porphyrin metabolism, sphingolipid metabolism, and lipopolysaccharide biosynthesis, presenting changes opposite to those observed in 100 μg/L LA-treated K. mikimotoi. Overall, this study revealed the metabolic response of K. mikimotoi to LA, enriching our understanding on the allelochemical mechanism of LA on K. mikimotoi.

Temperature and Photoperiod Affect the Sensitivity of Biofilms to Nickel and its Accumulation

Whereas metal impacts on fluvial communities have been extensively investigated, effects of abiotic parameters on community responses to contaminants are poorly documented. Variations in photoperiod and temperature commonly occur over the course of a season and could affect aquatic biofilm communities and their responses to contaminants. Our objective was to characterize the influence of environmental conditions (photoperiod and temperature) on nickel (Ni) bioaccumulation and toxicity using a laboratory-grown biofilm. Environmental parameters were chosen to represent variations that can occur over the summer season. Biofilms were exposed for 7 days to six dissolved Ni treatments (ranging from 6 to 115 µM) at two temperatures (14 and 20 °C) using two photoperiods (16:8 and 12:12-h light:dark cycle). Under these different scenarios, structural (dry weight biomass and chlorophyll-a) and functional biomarkers (photosynthetic yield and Ni content) were analyzed at four sampling dates, allowing us to evaluate Ni sensitivity of biofilms over time. The results highlight the effects of temperature on Ni accumulation and tolerance of biofilms. Indeed, biofilms exposed at 20 °C accumulated 1.6-4.2-fold higher concentrations of Ni and were characterized by a lower median effect concentration value using photosynthetic yield compared with those exposed at 14 °C. In terms of photoperiod, significantly greater rates of Ni accumulation were observed at the highest tested Ni concentration for biofilms exposed to a 12:12-h compared with a 16:8-h light:dark cycle. Our study demonstrates the influence of temperature on biofilm metabolism and illustrates that environmental factors may influence Ni accumulation response and thus Ni responses of phototrophic biofilms. Environ Toxicol Chem 2022;41:1649-1662. © 2022 SETAC.

Metabolomics insight into the influence of environmental factors in responses of freshwater biofilms to the model herbicide diuron

Freshwater biofilms have been increasingly used during the last decade in ecotoxicology due to their ecological relevance to assess the effect(s) of environmental stress at the community level. Despite growing knowledge about the effect of various stressors on the structure and the function of these microbial communities, a strong research effort is still required to better understand their response to chemical stress and the influence of environmental stressors in this response. To tackle this challenge, untargeted metabolomics is an approach of choice because of its capacity to give an integrative picture of the exposure to multiple stress and associated effect as well as identifying the molecular pathways involved in these responses. In this context, the present study aimed to explore the use of an untargeted metabolomics approach to unravel at the molecular/biochemical level the response of the whole biofilm to chemical stress and the influence of various environmental factors in this response. To this end, archived high-resolution mass spectrometry data from previous experiments at our laboratory on the effect of the model photosynthesis inhibitor diuron on freshwater biofilm were investigated by using innovative solutions for OMICs data (e.g., DRomics) and more usual chemometric approaches (multivariate and univariate statistical analyses). The results showed a faster (1 min) and more sensitive response of the metabolome to diuron than usual functional descriptors, including photosynthesis. Also, the metabolomics response to diuron resulted from metabolites following various trends (increasing, decreasing, U/bell shape) along increasing concentration and time. This metabolomics response was influenced by the temperature, photoperiod, and flow. A focus on a plant-specific omega-3 (eicosapentaenoic acid) playing a key role in the trophic chain highlighted the potential relevance of metabolomics approach to establish the link between molecular alteration and ecosystem structure/functioning impairment but also how complex is the response and the influence of all the tested factors on this response at the metabolomics level. Altogether, our results underline that more fundamental researches are needed to decipher the metabolomics response of freshwater biofilm to chemical stress and its link with physiological, structural, and functional responses toward the unraveling of adverse outcome pathways (AOP) for key ecosystem functions (e.g., primary production).

The water temperature changes the effect of pH on copper toxicity to the green microalgae Raphidocelis subcapitata

Rising temperature enhances the algal growth, which in turn increases the water pH. Ecotoxicity studies have suggested that copper becomes more toxic to microalgae species by increasing the temperature (within 20-30 °C) and pH. In this study, the joined effect of pH and temperature on copper toxicity to the microalgae Raphidocelis subcapitata was investigated using acclimated cells. Algal growth and toxicity tests were conducted using the medium recommended by the Organisation for Economic Co-operation and Development (OECD medium) at pH 6, 7, and 8 units from 15 to 30 °C, spaced by 3 °C. The specific growth rate of R. subcapitata increased by raising the pH and temperature, attributed to the higher membrane permeability and metabolism. The ecotoxicity tests showed that temperature changes the effect of pH on copper toxicity. Copper became less toxic when rising the temperature from 15 to 18 °C and from 6 to 8 pH-unit, suggesting that high pH controls copper bioavailability and toxicity. In contrast, from 21 to 30 °C, the effect of copper was not significantly altered by temperature, but it became more toxic at high pH. Results of this study warn about the higher risk of copper in cold seasons rather than warm conditions.

Fatty acid profile as an efficient bioindicator of PCB bioaccumulation in a freshwater lake food web: A stable isotope guided investigation

In past studies, the health and ecological risks of PCBs are well established. The impact of low-dose PCBs on aquatic ecosystems for an extended period is a matter of concern in the current era. The application of fatty acids (FAs) as bioindicators of pollution in the freshwater food web is almost unavailable. This study investigated concentrations of 209 PCB congeners, stable isotope levels, and FAs composition in ten freshwater species of Dongtinghu Lake, China. Total PCB congeners (∑PCBs) concentrations were ranged from 4.17 to 38.35 ng/g lipid weight. A total of 84 PCB congeners were detected out of 209 target PCB congeners, particularly PCB101, 118, 138, 153, and 155 found in all samples. The concentrations of 24 PCB congeners increased with trophic levels, but PCB 155 concentrations were consistent throughout trophic levels. The toxic equivalents (TEQ) of dl-PCBs (mostly PCB 126 and 169) also increased with trophic levels Out of total 35 FAs, 21 FAs were significantly positively correlated with 43 PCB congeners. Among FAs, C16:0 was the most abundant and positively correlated with most PCB compounds. Positive correlations between FAs and PCBs indicated that FAs can be used as efficient bioindicators of PCBs pollution in the aquatic food web.

Thorium Exposure Drives Fatty Acid and Metal Transfer from Biofilms to the Grazer Lymnaea sp

Aquatic ecotoxicological risks associated with tetravalent metallic elements such as thorium (Th) are still poorly understood. Periphytic biofilm represents an important food source in aquatic environments; thus, such risks could severely affect nutrient and energy cycling in these ecosystems. The present study investigated the potential for Th to change the fatty acid composition of biofilm communities. Bioaccumulation of Th and fatty acids were measured after 4 wk to 2 exposure conditions: a control (C0) and Th exposure (C10). Some major fatty acids such as C16:1n-7 and docosahexaenoic acid C22:6n-3 differed significantly between control and C10 conditions. To determine if Th can be trophically transferred and to investigate the impacts of nutritional quality changes on primary consumers, common pond snails (Lymnaea sp.) were fed for 4 wk with control and Th-exposed biofilm. Thorium appeared to be trophically transferable to the grazers, although we cannot exclude that part of the Th accumulated by the snails may have been taken from the water through release from the biofilms. The composition of major fatty acids observed in the grazers was also significantly affected, notably by a decrease of total polyunsaturated fatty acids. These results indicate that very low Th concentrations can decrease the nutritional quality of organisms at the base of the food chain. Environ Toxicol Chem 2021;40:2220-2228. © 2021 SETAC.

Evaluation of the differences between biofilm and planktonic Brucella abortus via metabolomics and proteomics

This study analyzed the difference between biofilm and planktonic Brucella abortus using metabolomics and proteomics. Brucella abortus was cultured in different media to induce Brucella abortus biofilm formation and planktonic cells, followed by metabolomics and proteomics analyses for these two samples. Significant differential metabolites were identified, followed by KEGG pathway analysis. Differentially expressed proteins were identified, followed by subcellular localization, GO annotation, and KEGG pathway enrichment. Additionally, a correlation analysis of metabolomics and proteomics was performed. Metabolomics analysis showed 7682 positive and 4433 negative metabolites, including 188 positive and 117 negative significant differential metabolites. These differential metabolites were enriched in fatty acid/unsaturated fatty acid biosynthesis and linoleic acid metabolism. Proteomics analysis revealed 1759 proteins, including 486 differentially expressed proteins, which were enriched in various metabolic and degradation-related pathways. Subcellular localization showed that 74.3% of the differential proteins were cytoplasmic proteins. Correlation analysis showed that 1-palmitoyl-2-oleoyl-phosphatidylglycerol had the most significant correlations with proteins, followed by cytosine. Both metabolites correlated with the protein Q57EI7 (RbsB-1, ribose ABC transporter). One common pathway, fatty acid biosynthesis, was identified by both proteomics and metabolomics analyses that involved the metabolites, oleic acid, and protein Q57DK3 (biotin carboxylase). There were metabolomic and proteomic differences between Brucella abortus biofilm and planktonic cells, and these results provide novel insights into the biofilm-forming process of Brucella abortus.

Effects of Temperature and Glyphosate on Fatty Acid Composition, Antioxidant Capacity, and Lipid Peroxidation in the Gastropod Lymneae sp

Little is known about the potential effects of glyphosate on freshwater gastropods and possible interactions between glyphosate and other stressors. A two-way factorial experiment was conducted to investigate the effects of temperature (20 °C/25 °C) and glyphosate (0 µg/L/200 µg/L) on Lymnaea sp. After 21 days, antioxidant capacity (superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and glutathione-S-transferase (GST)), malondialdehyde content (MDA), and fatty acid (FA) composition of Lymnaea sp. tissue were measured. Temperature had an effect on SOD activity and GPx activity. In contrast, an increase in GST activity was observed in glyphosate-exposed snails, highlighting the role of GST in the glyphosate detoxification process. Differences in temperature and glyphosate did not affect lipid peroxidation (MDA); however, we observed a trend suggesting the presence of higher MDA content in glyphosate-exposed snails at 20 °C. The FA groups were generally not strongly affected by the treatments, except for omega−9 (n-9) that was markedly lower at the higher temperature. Changes were also observed in individual FA as a response to glyphosate and/or temperature. For example, a significant decrease in 18:1n9 was observed at 25 °C. Our results showed that antioxidant capacity and FA profiles were mainly affected by temperature, while glyphosate seemed to have a lesser impact.

Lipid Accumulation by Xylose Metabolism Engineered Mucor circinelloides Strains on Corn Straw Hydrolysate

Previously, we presented a novel approach for increasing the consumption of xylose and the lipid yield by overexpressing the genes coding for xylose isomerase (XI) and xylulokinase (XK) in Mucor circinelloides. In the present study, an in-depth analysis of lipid accumulation by xylose metabolism engineered M. circinelloides strains (namely Mc-XI and Mc-XK) using corn straw hydrolysate was to be explored. The results showed that the fatty acid contents of the engineered M. circinelloides strains were, respectively, increased by 19.8% (in Mc-XI) and 22.3% (in Mc-XK) when compared with the control strain, even though a slightly decreased biomass in these engineered strains was detected. Moreover, the xylose uptake rates of engineered strains in the corn straw hydrolysate were improved significantly by 71.5% (in Mc-XI) and 68.8% (in Mc-XK), respectively, when compared with the control strain. Maybe the increased utilization of xylose led to an increase in lipid synthesis. When the recombinant M. circinelloides strains were cultured in corn straw hydrolysate medium with the carbon-to-nitrogen ratio (C/N ratio) of 50 and initial pH of 6.0, at 30 °C and 500 rpm for 144 h, a total biomass of 12.6-12.9 g/L with a lipid content of 17.2-17.7% (corresponding to a lipid yield of 2.17-2.28 g/L) was achieved. Our study provides a foundation for the further application of the engineered M. circinelloides strains to produce lipid from lignocelluloses.