Elucidating Microbial Iron Corrosion Mechanisms with a Hydrogenase-deficient Strain of

Sulfate-reducing microorganisms extensively contribute to the corrosion of ferrous metal infrastructure. There is substantial debate over their corrosion mechanisms. We investigated Fe corrosion with , the sulfate reducer most often employed in corrosion studies. Cultures were grown with both lactate and Fe as potential electron donors to replicate the common environmental condition in which organic substrates help fuel the growth of corrosive microbes. Fe was corroded in cultures of a hydrogenase-deficient mutant with the 1:1 correspondence between Fe loss and H accumulation expected for Fe oxidation coupled to H reduction to H. This result and the extent of sulfate reduction indicated that was not capable of direct Fe-to-microbe electron transfer even though it was provided with a supplementary energy source in the presence of abundant ferrous sulfide. Corrosion in the hydrogenase-deficient mutant cultures was greater than in sterile controls, demonstrating that H removal was not necessary for the enhanced corrosion observed in the presence of microbes. The parental H-consuming strain corroded more Fe than the mutant strain, which could be attributed to H oxidation coupled to sulfate reduction, producing sulfide that further stimulated Fe oxidation. The results suggest that H consumption is not necessary for microbially enhanced corrosion, but H oxidation can indirectly promote corrosion by increasing sulfide generation from sulfate reduction. The finding that was incapable of direct electron uptake from Fe reaffirms that direct metal-to-microbe electron transfer has yet to be rigorously described in sulfate-reducing microbes.