Electrochemical and molecular characterization of electroactive biofilms on stainless steel in marine environment

Abstract : Microorganisms increase the opencircuit potential of stainless Steel immersed in seawater in a phenomenon called ennoblement.This change of potential of several hundreds of millivolts raises the chance of localized corrosion.The ennoblement has been studied for more than 40 years, and despite the importance and impact of ennoblement, little is known about the microbial mechanisms responsible for the phenomenon. We have combined microbial ecology and electrochemistry to investigate the diversity of surface attached bacteria associated with stainless steel ennoblement. Seawater temperature and dissolved oxygen content are factors that influence the ennoblement and we used them to infer the bacterial fraction associated with the phenomenon. The ennoblement is inhibited by a critical seawater tempzrature (above 38°C/40°C) and low dissolved oxygen content.With DNA amplicon sequencing, we identified operational taxonomie units (OTUs) that were biomarkers of the ennoblement. There were some OTUs affiliated to hydrocarbon degrading bacteria, and one OTU affiliated to ‘Candidatus Tenderia electrophaga’, an electrotrophic bacteria able to reduce oxygen with electrons from an electrode.We investigated the role of electrotrophic bacteria with potentiostatic and open circuit conditions and with metagenomics we recovered a metagenome assembled genome (MAG) very close to 'Candidatus Tenderia electrophaga’ associated with the ennoblement.From these results, we proposed a new bacterial mechanism to explain the ennoblement : electrotrophic bacteria would be able to reduce oxygen with électron drawn from the stainless steel passivation film, hence influencing the open circuit potential and therefore the ennoblement.
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Florian Trigodet. Electrochemical and molecular characterization of electroactive biofilms on stainless steel in marine environment. Microbiology and Parasitology. Université de Bretagne occidentale - Brest, 2019. English. ⟨NNT : 2019BRES0029⟩. ⟨tel-02307295⟩

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