Influence of Temperature and Nickel on Algal Biofilm Fatty Acid Composition

Abstract

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.

A glance at the French-speaking diatomist community (ADLaF 2019 meeting)

“…For this purpose, microbial fatty acids emerge as relevant proxies of ecosystem health (e.g. Fadhlaoui et al 2020). Among abiotic stressors mentioned during the meeting (pesticides, nanoparticles, natural radioactivity…), the expected increase in frequency and intensity of extreme events due to climate change is a concern shared by both freshwater and marine diatomists: parallel works are ongoing to evaluate the effects of heat waves on benthic diatoms of intertidal mudflats and intermittent rivers (Béchet et al 2017).…”

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

“…Total lipids were extracted from the whole biofilm in those aliquots according to Folch et al (1957). The detailed procedure for lipid extraction was described in Fadhlaoui et al (2020). Total lipids were extracted in a chloroform/methanol mix (1/2 v/v).…”

“…The ICP-MS calibration curve was validated with certified control solution 406 (SCP Science). Thorium in the biofilm and in the snails was determined after samples were lyophilized and digested according to Fadhlaoui et al (2020). Aqueous Th concentrations in the biofilm exposure media as well as in the snail water were monitored weekly during the experiment.…”

“…The presence of contaminants, such as metals, could impact aquatic food webs by affecting fatty acid synthesis (Drerup and Vis 2018; Fadhlaoui et al 2020). Metallic contaminants can generate oxidative stress, and the PUFAs composing the cell membrane are especially prone to lipid peroxidation (Rocchetta et al 2006).…”

“…by altering glycerophospholipid biosynthesis pathways (Zhang et al 2015). In addition, it is well established that benthic microorganisms can internalize metallic elements such as selenium (Conley et al 2013), cadmium (Xie et al 2010), zinc (Kim et al 2012), copper (Meylan et al 2004), and nickel (Fadhlaoui et al 2020) and can retain them up to several days after exposure (Holding et al 2003). Because diet can be a predominant source of metal exposure (Luoma and Rainbow 2005), the capacity for periphytic biofilm to bioaccumulate metals can affect its consumers (Xie et al 2010; Cain et al 2011; Conley et al 2011).…”