Abstract: Microbes can cause or accelerate metal corrosion, leading to huge losses in corrosion damages each year. Geobacter sulfurreducens is a representative electroactive bacterium in many soils, sediments, and wastewater systems. It has been confirmed to directly extract electrons from elemental metals. However, little is known about the effect of electron shuttles in G. sulfurreducens corrosion on stainless steel. In this study, we report that exogenous flavins promote iron-to-microbe electron transfer, accelerating microbial corrosion. G. sulfurreducens caused 1.3 times deeper pits and increased electron uptake (with 2 times increase of i_corr) from stainless steel when riboflavin was added to the culture medium. OmcS-deficient mutant data suggest that G. sulfurreducens utilizes riboflavin as a bound-cofactor in outer membrane c-type cytochromes. The finding that, in the presence of microbes, riboflavin can substantially accelerate corrosion highlights the role of flavin redox cycling for enhanced iron-to-microbe electron transfer by G. sulfurreducens and provides new insights in microbial corrosion.

Key words: Extracellular electron transfer, Microbiological corrosion, Geobacter sulfurreducens, Outer membrane c-type cytochromes, Exogenous flavins