Electrically conductive nanowires controlled one pivotal route in energy harvest and microbial corrosion via direct metal-microbe electron transfer

Extracellular electron transfer(EET)plays a critical role in bioelectrochemical processes,allowing cou-pling between microorganisms and extracellular solid-state electrodes,metals,or other cells in energy metabolism.Previous studies have suggested a role for outer-surface c-type cytochromes in direct metal-to-microbe electron transfer by Geobacter sulfurreducens,a model electroactive bacterium.Here,we ex-amined the possibility of other microbially produced electrical contacts by deleting the gene for PilA,the protein monomer that G.sulfurreducens assembles into electrically conductive protein nanowires(e-pili).Deleting pilA gene inhibited electron extraction from pure iron and 316L stainless steel up to 31%and 81%,respectively more than deleting the gene for the outer-surface cytochrome OmcS.This PilA-deficient phenotype,and the observation that relatively thick biofilms(21.7μm)grew on the metal surfaces at multi-cell distances from the metal surfaces suggest that e-pili contributed significantly to microbial cor-rosion via direct metal-to-microbe electron transfer.These results have implications for the fundamental understanding of electron harvest via e-pili by electroactive microbes,their uses in bioenergy production,as well as in monitoring and mitigation of metal biocorrosion.