Elucidating microbial iron corrosion mechanisms with a hydrogenase-deficient strain of Desulfovibrio vulgaris .

Sulfate-reducing microorganisms extensively contribute to the corrosion of ferrous metal infrastructure. There is substantial debate over their corrosion mechanisms. We investigated Fe 0 corrosion with Desulfovibrio vulgaris , the sulfate reducer most often employed in corrosion studies. Cultures were grown with both lactate and Fe 0 as potential electron donors to replicate the common environmental condition in which organic substrates help fuel the growth of corrosive microbes. Fe 0 was corroded in cultures of a D. vulgaris hydrogenase-deficient mutant with the 1:1 correspondence between Fe 0 loss and H 2 accumulation expected for Fe 0 oxidation coupled to H + reduction to H 2 . This result and the extent of sulfate reduction indicated that D. vulgaris was not capable of direct Fe 0 -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 2 removal was not necessary for the enhanced corrosion observed in the presence of microbes. The parental H 2 -consuming strain corroded more Fe 0 than the mutant strain, which could be attributed to H 2 oxidation coupled to sulfate reduction, producing sulfide that further stimulated Fe 0 oxidation. The results suggest that H 2 consumption is not necessary for microbially enhanced corrosion, but H 2 oxidation can indirectly promote corrosion by increasing sulfide generation from sulfate reduction. The finding that D. vulgaris was incapable of direct electron uptake from Fe 0 reaffirms that direct metal-to-microbe electron transfer has yet to be rigorously described in sulfate-reducing microbes.