Abstract

A fundamental question in subsurface microbiology is; what are the active metabolisms supporting resident populations? Due to the limited organic electron donors available in most deep-sea marine environments, solid phase mineral electron donors have been suggested to be important electron sources. However, the lack of knowledge surrounding mechanisms of electron uptake in lithotrophic organisms, coupled with the difficulty of monitoring redox changes in solid substrates, limits our ability to assess the importance of mineral oxidation in most environments. We utilized controlled electrochemical techniques to mimic solid phase electron donors for studying microbial extracellular electron transfer (EET) in a deep-sea marine sediment community. Specifically this work used a stimulus-induced metagenomic/ metatranscriptomic approach on enriched electrode communities in order to: 1) identify transcriptionally active putative mineral oxidizing microbes and 2) identify gene targets that are differentially regulated in response to reducing poised electrode potentials with genetic features that suggest involvement in EET. Our work demonstrated electron uptake in deep-sea marine sediment from Monterey Canyon, CA, and enhanced EET reactions with changes in redox potential. Community analysis of enriched electrode communities highlighted groups potentially involved in EET activity. Metagenomic and metatranscriptomic analysis has identified organisms in the Rhodobacteraceae as important players in electrode oxidation. The organisms and pathways highlighted using this culture independent approach will help inform potential genetic markers for future studies as well as aid in developing a framework for detecting EET capabilities in environmentally relevant microbes.

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