Carboxydotrophic growth of <i>Geobacter sulfurreducens</i>

This study shows that Geobacter sulfurreducensgrows on carbon monoxide (CO) as electron donor with fumarateas electron acceptor. Geobacter sulfurreducens wastolerant to high CO levels, with up to 150 kPa in the headspacetested. During growth, hydrogen was detected in very slightamounts (~5 Pa). In assays with cell-free extract of cellsgrown with CO and fumarate, production of hydrogen fromCO was not observed, and hydrogenase activity with benzylviologen as electron acceptor was very low. Taken together,this suggested that CO is not utilized via hydrogen as intermediate.In the presence of CO, reduction of NADP+ wasobserved at a rate comparable to CO oxidation coupled tofumarate reduction in vivo. The G. sulfurreducens genomecontains a single putative carbon monoxide dehydrogenaseencodinggene. The gene is part of a predicted operon alsocomprising a putative Fe–S cluster-binding subunit (CooF)and a FAD–NAD(P) oxidoreductase and is preceded by aputative CO-sensing transcription factor. This cluster may beinvolved in a novel pathway for CO oxidation, but furtherstudies are necessary to ascertain this. Similar gene clustersare present in several other species belonging to theDeltaproteobacteria and Firmicutes, for which CO utilizationis currently not known