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Abstract Title: Transcriptomic Evidence for Versatile Metabolic Activities of Mercury Cycling Microorganisms in Brackish Microbial Mats
Presenter Name: Adrien Vigneron
Company/Institution: Université de Pau et des Pays de l’Adour, E2S UPPA, CNRS, IPREM, Pau, France
Session: Special Session - Meta-omic and geochemical approaches to linking microbial activity to biogeochemical mercury cycling
Day and Session: Friday 29th July - Session One
Start Time: 06:00 UTC
Co-Authors: Adrien Vigneron

Abstract Information :

Methylmercury, biomagnifying through food chains, is highly toxic for aquatic life. Its production and degradation are largely driven by microbial transformations, however diversity and metabolic activity of mercury transformers, resulting in methylmercury concentrations in environments remain poorly understood. Microbial mats are thick biofilms where oxic and anoxic metabolisms co-occur, providing opportunities to investigate the complexity of the microbial mercury transformations over contrasted redox conditions. We conducted a genome-resolved metagenomic and metatranscriptomic analysis of two microbial mats strongly contaminated by mercury to identify putative activity of mercury reducers; methylators and demethylators in the system. Our transcriptomic results revealed the major role of rare microorganisms in mercury cycling. Mercury methylators, mainly related to Desulfobacterota, expressed a large panel of metabolic activities in sulfur, iron, nitrogen and halogen compound transformations, extending known activities of mercury methylators under suboxic to anoxic conditions. Methylmercury detoxification processes were dissociated in the microbial mats with methylmercury cleavage being carried out by sulfide-oxidizing Thiotrichaceae and Rhodobacteraceae populations, whereas mercury reducers included members of the Verrucomicrobia, Bacteroidetes, Gammaproteobacteria and different populations of Rhodobacteraceae. However most of the mercury reduction was potentially carried out anaerobically by sulfur- and iron-reducing Desulfuromonadaceae, revising our understanding of mercury transformers ecophysiology.

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