biofilm metagenome Metagenome

Freshwater biofilms are a consortium of microorganisms, such as algae and bacteria, harbored in an exopolymeric substance matrix and living onto substrata. They are important drivers of key biogeochemical processes (cycle of organic carbon nutrient…). Biofilms are also known to influence mercury (Hg) cycle through its bioaccumulation, transformations and transfer to the food chain, however little is known about its impacts on biofilms. The aim of this study was to examine Hg effects onto the biofilm taxonomic composition. Biofilms were cultivated in three Hg concentrations (11 pM, 121 pM and 1.4 nM) under light and temperature controlled conditions using microcosms for 50 days . Bacteria and microalgae compositions were identified by amplicon sequencing to determine predominant phyla associated with these taxa. Both bacterial sequence numbers and richness increased with the increase of Hg exposure concentrations with Proteobacteria being the predominant phylum at all studied concentrations. In contrast, the number of microalgae sequences and richness were both found to decrease with the increase of Hg concentration exposure. The present study demonstrates that Hg can modify biofilm composition at much lower concentrations than those observed in the laboratory with model microorganisms.