Novel example of CO2 cathodic driven bioreduction by Shewanella oneidensis MR-1: possible implications for carbon cycling in deep oceans.
The University of Tokyo
The chimneys of black smoker vents are made of conductive catalytic material and the hydrothermal fluid of these vents is rich in highly reductive compounds like hydrogen sulfide, hydrogen gas and reduced metal ions . This leads to the formation of potential between the interior and the exterior of the chimneys, which might be able to induce cathodic CO2 fixation by electrochemically active microbes (EAM). Here we examined this hypothesis by using Shewanella oneidensis MR-1 as a model microbe for EAM, since there are a variety of reports concerning the presence of metal-reducing bacteria species like Shewanella  . Following the biofilm formation, we poised Indium-Tin Oxide electrode potential at -0.45 V vs SHE to monitor microbial cathodic CO2 reduction current (ICO2) as described previously. The injection of gaseous CO2 into the cell showed a significant current increase compared with inert Argon gas. Upon the addition of flavin ICO2 increased significantly (about 3 times). Given flavin specifically associate with outer-membrane c-type cytochrome complex (OM c-Cyts) to enhance the rate of electron uptake, our results suggest that cathodic electrons are transported to the cytoplasm and to the metabolic pathway reducing CO2 via OM c-Cyts . These findings suggest the possible contribution of EAM to the deep sea carbon cycle. We will show more data about experiments for CO2 reduction and discuss the potential metabolic pathway of reductive cycle based on the results of quantitative-PCR analysis.
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keywords:Shewanella oneidensis MR-1,Dark Carbon fixation,Biocathode,Bioelectrochemical system