Toward establishing minimum requirements for extracellular electron transfer in Geobacter sulfurreducens

<span class="paragraphSection"><div class="boxTitle">Abstract</div>The highly redundant pathways for extracellular electron transfer in <span style="font-style:italic;">Geobacter sulfurreducens</span> must be simplified for this microorganism to serve as an effective chassis for applications such as the development of sensors and biocomputing. Five homologs of the periplasmic <span style="font-style:italic;">c</span>-type cytochromes, PpcA-E, offer the possibility of multiple routes of electron transfer across the periplasm. The presence of a large number of outer membrane <span style="font-style:italic;">c</span>-type cytochromes allows <span style="font-style:italic;">G. sulfurreducens</span> to adapt to disruption of an electron transfer pathway in the outer membrane. A strain in which genes for all five periplasmic cytochromes, PpcA-E, were deleted did not reduce Fe(III). Introducing <span style="font-style:italic;">ppcA</span> under the control of an IPTG-inducible system in the quintuple deletion strain yielded a strain that reduced Fe(III) only in the presence of IPTG. A strain lacking known major outer membrane cytochromes, OmcB, OmcE, OmcS, and OmcT, and putative functional homologs of OmcB, did not reduce Fe(III). Introduction of <span style="font-style:italic;">omcB</span> in this septuple deletion strain restored the ability to reduce Fe(III). These results demonstrate that it is possible to trim redundancy from the extracellular electron transfer pathways in <span style="font-style:italic;">G. sulfurreducens</span> in order to construct strains with defined extracellular electron transfer routes.</span>

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