Magnetite compensates for the lack of a pilin‐associated <scp> <i>c</i> </scp> ‐type cytochrome in extracellular electron exchange

<jats:title>Summary</jats:title> <jats:p> Nanoscale magnetite can facilitate microbial extracellular electron transfer that plays an important role in biogeochemical cycles, bioremediation and several bioenergy strategies, but the mechanisms for the stimulation of extracellular electron transfer are poorly understood. Further investigation revealed that magnetite attached to the electrically conductive pili of <jats:styled-content style="fixed-case"> <jats:italic>G</jats:italic> </jats:styled-content> <jats:italic>eobacter</jats:italic> species in a manner reminiscent of the association of the multi‐heme <jats:styled-content style="fixed-case"> <jats:italic>c</jats:italic> </jats:styled-content> ‐type cytochrome <jats:styled-content style="fixed-case">OmcS</jats:styled-content> with the pili of <jats:styled-content style="fixed-case"> <jats:italic>G</jats:italic> </jats:styled-content> <jats:italic>eobacter sulfurreducens</jats:italic> . Magnetite conferred extracellular electron capabilities on an <jats:styled-content style="fixed-case">OmcS</jats:styled-content> ‐deficient strain unable to participate in interspecies electron transfer or <jats:styled-content style="fixed-case">Fe</jats:styled-content> ( <jats:styled-content style="fixed-case">III</jats:styled-content> ) oxide reduction. In the presence of magnetite wild‐type cells repressed expression of the <jats:styled-content style="fixed-case">OmcS</jats:styled-content> gene, suggesting that cells might need to produce less <jats:styled-content style="fixed-case">OmcS</jats:styled-content> when magnetite was available. The finding that magnetite can compensate for the lack of the electron transfer functions of a multi‐heme <jats:styled-content style="fixed-case"> <jats:italic>c</jats:italic> </jats:styled-content> ‐type cytochrome has implications not only for the function of modern microbes, but also for the early evolution of microbial electron transport mechanisms. </jats:p>