H(2) Is a Major Intermediate in Desulfovibrio vulgaris Corrosion of Iron

Desulfovibrio vulgaris has been a primary pure culture sulfate reducer for developing microbial corrosion concepts. Multiple mechanisms for how it accepts electrons from Fe(0) have been proposed. We investigated Fe(0) oxidation with a mutant of D. vulgaris in which hydrogenase genes were deleted. The hydrogenase mutant grew as well as the parental strain with lactate as the electron donor, but unlike the parental strain, it was not able to grow on H(2). The parental strain reduced sulfate with Fe(0) as the sole electron donor, but the hydrogenase mutant did not. H(2) accumulated over time in Fe(0) cultures of the hydrogenase mutant and sterile controls but not in parental strain cultures. Sulfide stimulated H(2) production in uninoculated controls apparently by both reacting with Fe(0) to generate H(2) and facilitating electron transfer from Fe(0) to H(+). Parental strain supernatants did not accelerate H(2) production from Fe(0), ruling out a role for extracellular hydrogenases. Previously proposed electron transfer between Fe(0) and D. vulgaris via soluble electron shuttles was not evident. The hydrogenase mutant did not reduce sulfate in the presence of Fe(0) and either riboflavin or anthraquinone-2,6-disulfonate, and these potential electron shuttles did not stimulate parental strain sulfate reduction with Fe(0) as the electron donor. The results demonstrate that D. vulgaris primarily accepts electrons from Fe(0) via H(2) as an intermediary electron carrier. These findings clarify the interpretation of previous D. vulgaris corrosion studies and suggest that H(2)-mediated electron transfer is an important mechanism for iron corrosion under sulfate-reducing conditions.