Abstract: Microbiologically influenced corrosion (MIC) of iron-based metals mediated by sulfate-reducing bacteria (SRB) incurs substantial economic costs, with its mechanisms yet to be thoroughly deciphered. The classical cathodic depolarization theory (CDT) has been used to explain SRB-mediated metal carbon steel corrosion, implicating hydrogenases as a crucial factor, but with no direct molecular biology evidence. This study aims to elucidate the involvement of hydrogenases in MIC, using Nitratidesulfovibrio vulgaris Hildenborough (NvH) as a model organism, which lacks annotated c-cytochromes in its genome. We found that the Hyd hydrogenase in NvH is involved in MIC acceleration caused by carbon source starvation due to increased electron harvest from carbon steel, in which the expression level of the Hyd gene is upregulated. However, combined with genetic manipulation, electrochemical analysis, and corrosion morphology characterizations, we concluded that hydrogenases are non-essential to MIC by NvH, as the deletion of all hydrogenase genes did not significantly decelerate corrosion. This suggests that there are alternate routes for electron transfer in NvH MIC. These insights call for a reassessment of the role of hydrogenases in SRB-MIC of carbon steel in the CDT theory, which relies on an SRB biofilm removal of hydrogen on the metal surface by hydrogenases.

Key words: Microbiologically influenced corrosion, Sulfate-reducing bacteria, Cathodic depolarization theory, Hydrogenase, Nitratidesulfovibrio vulgaris Hildenborough