Genetic studies reveal that H₂ is a key electron donor for Desulfovibrio ferrophilus during iron corrosion

The mechanisms for electron transfer from Fe⁰ to Desulfovibrio ferrophilus during the corrosion of ferrous metals are of interest because of its importance as a model corrosive microbe. H₂ is often an important intermediary electron carrier between Fe⁰ and other microbes and thus the possibility of electron transfer via H₂ was investigated by constructing a hydrogenase-deficient gene deletion mutant strain of D. ferrophilus unable to consume H₂. Standard corrosion measures of weight loss, pitting, and corrosion current revealed that Fe⁰ coupons were corroded significantly faster in the presence of D. ferrophilus than in sterile controls. In contrast, corrosion in the presence of the hydrogenase-deficient mutant was even less than in sterile controls. Although H₂ accumulated over time in sterile controls and in the presence of the hydrogenase-deficient mutant during Fe⁰ corrosion, no H₂ was detected with wild-type cells. An unknown electron transfer route supporting low levels of sulfate reduction was apparent in the hydrogenase-deficient mutant, but the significance of this route in wild-type cells will be difficult to assess because of the apparent dominance of the H₂-based route. Therefore, even though direct metal-to-microbe electron transfer has often been hypothesized to be the primary route for D. ferrophilus electron uptake during ferrous metal corrosion, the results of our gene deletion study suggest that H₂ is a major intermediary electron carrier.