The aim of this study was to investigate the combined effects of temperature and metal contamination (cadmium and nickel) on phospholipid fatty acid composition, antioxidant enzyme activities and lipid peroxidation in fish. Yellow perch were acclimated to two different temperatures (9°C and 28°C) and exposed either to Cd or Ni (respectively 4μg/L and 600μg/L) for seven weeks. Superoxide dismutase, catalase, glutathione-S-transferase, glutathione peroxidase activities and glutathione concentration were measured as indicators of antioxidant capacities, while malondialdehyde concentration was used as an indicator of lipid peroxidation. Poikilotherms including fish counteract the effects of temperature on phospholipid fatty acid ordering by remodelling their composition to maintain optimal fluidity. Accordingly, in our study, the fatty acid composition of yellow perch muscle at 9°C was enhanced in monounsaturated (MUFA) and polyunsaturated fatty acids (PUFA) compared to fish maintained at 28°C, in agreement with the theory of homeoviscous adaptation. Using ratios of various fatty acids as surrogates for desaturase and elongase activities, our data suggests that modification of the activity of these enzymes is responsible for the thermal acclimation of phospholipid fatty acid profiles. However, this response was altered under Ni and Cd exposure: PUFA decreased (specifically n-6 PUFA) while the proportion of saturated fatty acids increased at 9°C, whereas at 28°C, PUFA increased to proportions exceeding those observed at 9°C. Lipid peroxidation could be observed under all experimental conditions. Both enzymatic and non-enzymatic antioxidant defense systems acted cooperatively to cope with oxidative stress leading to lipid peroxidation, which was not affected by temperature acclimation as indicated by malondialdehyde concentration, in spite of a higher polyinsaturation in cold-acclimated fish which would be predicted to increase their vulnerability to peroxidation. However, in warm-acclimated, Ni-exposed fish, in which the highest proportion of PUFA was observed, lower concentrations of malondialdehyde were measured, suggesting an overcompensation of antioxidant mechanisms in these fish which could represent a substantial metabolic cost and explain their lower condition.

Freshwater biofilms play an important role in aquatic ecosystems and are widely used to evaluate environmental conditions. Little is known about the effects of temperature and metals on biofilm fatty acid (FA) composition. In this study, we exposed a natural biofilm cultured in mesocosms to a gradient of nickel (Ni) concentrations at 15 and 21°C during 28 days. Metal bioaccumulation, algal taxonomic composition and biofilm FA profiles were determined. At both temperatures, bioaccumulated Ni increased This article is protected by copyright. All rights reserved. Accepted Articlewith Ni exposure concentration and reached the highest values at 25 μM Ni, followed by a decrease at 55 and 105 μM Ni. In control biofilms, palmitic acid (16:0), palmitoleic acid (16:1n7), oleic acid (18:1n9), linoleic acid (18:2n6) and linolenic acid (18:3n3) were the dominant FA at 15 and 20°C. This composition suggests a dominance of cyanobacteria and green algae, which was subsequently confirmed by microscope observations. The increase in temperature resulted in a decrease in the ratio unsaturated:saturated FA, which is considered as an adaptive response to temperature variation. Polyunsaturated FA tended to decrease along the Ni gradient, as opposed to saturated FA which increased with Ni concentrations. Temperature and Ni affected differently the estimated desaturase and elongase activities (product/precursor ratios). The increase in PUFA at 15°C is concomitant to an increase in Δ9-desaturase (D9D). The estimated activities of (D9D), Δ12-desaturase (D12D) and Δ15-desaturase (D15D) decreased along the Ni gradient and reflected a decline in PUFA. The elevated estimated elongase activity (ELOVL) reflected the observed increase in SFA at the highest Ni exposure concentration (105 µM). Our results suggest that FA could be used as endpoint to evaluate environmental perturbations.

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.

In this study, we tested the hypothesis that metal exposure affected the normal thermal response of cell membrane FA composition and of elongase and desaturase gene transcription levels. To this end, muscle and brain membrane FA composition and FA desaturase (fads2, degs2 and scd2) and elongase (elovl2, elovl5 and elovl6) gene transcription levels were analyzed in fathead minnows (Pimephales promelas) acclimated for eight weeks to 15, 25 or 30°C exposed or not to cadmium (Cd, 6μg/l) or nickel (Ni, 450 6μg/l). The response of membrane FA composition to temperature variations or metal exposure differed between muscle and brain. In muscle, an increase of temperature induced a decrease of polyunsaturated FA (PUFA) and an increase of saturated FA (SFA) in agreement with the current paradigm. Although a similar response was observed in brain between 15 and 25°C, at 30°C, brain membrane unsaturation was higher than predicted. In both tissues, metal exposure affected the normal thermal response of membrane FA composition. The transcription of desaturases and elongases was higher in the brain and varied with acclimation temperature and metal exposure but these variations did not generally reflect changes in membrane FA composition. The mismatch between gene transcription and membrane composition highlights that several levels of control other than gene transcription are involved in adjusting membrane FA composition, including post-transcriptional regulation of elongases and desaturases and de novo phospholipid biosynthesis. Our study also reveals that metal exposure affects the mechanisms involved in adjusting cell membrane FA composition in ectotherms.

No abstract