A Geobacter sulfurreducens Strain Expressing Pseudomonas aeruginosa Type IV Pili Localizes OmcS on Pili but Is Deficient in Fe(III) Oxide Reduction and Current Production

<jats:title>ABSTRACT</jats:title> <jats:p> The conductive pili of <jats:named-content content-type="genus-species">Geobacter</jats:named-content> species play an important role in electron transfer to Fe(III) oxides, in long-range electron transport through current-producing biofilms, and in direct interspecies electron transfer. Although multiple lines of evidence have indicated that the pili of <jats:named-content content-type="genus-species">Geobacter sulfurreducens</jats:named-content> have a metal-like conductivity, independent of the presence of <jats:italic>c</jats:italic> -type cytochromes, this claim is still controversial. In order to further investigate this phenomenon, a strain of <jats:named-content content-type="genus-species">G. sulfurreducens</jats:named-content> , designated strain PA, was constructed in which the gene for the native PilA, the structural pilin protein, was replaced with the PilA gene of <jats:named-content content-type="genus-species">Pseudomonas aeruginosa</jats:named-content> PAO1. Strain PA expressed and properly assembled <jats:named-content content-type="genus-species">P. aeruginosa</jats:named-content> PilA subunits into pili and exhibited a profile of outer surface <jats:italic>c</jats:italic> -type cytochromes similar to that of a control strain expressing the <jats:named-content content-type="genus-species">G. sulfurreducens</jats:named-content> PilA. Surprisingly, the strain PA pili were decorated with the <jats:italic>c</jats:italic> -type cytochrome OmcS in a manner similar to the control strain. However, the strain PA pili were 14-fold less conductive than the pili of the control strain, and strain PA was severely impaired in Fe(III) oxide reduction and current production. These results demonstrate that the presence of OmcS on pili is not sufficient to confer conductivity to pili and suggest that there are unique structural features of the <jats:named-content content-type="genus-species">G. sulfurreducens</jats:named-content> PilA that are necessary for conductivity. </jats:p>