P005
Electron-acceptor limitation triggers exocellular electron
transfer in planktonic culture of Geobacter sulfurreducens
Cristina Gutiérrez Garrán1, Zulema Borjas2,
Marta Estevez1, Tristano Baccheti1, Derek Lovley3
and Abraham Esteve-Nuñez1
1
University of Alcalá, Madrid, Spain
2
IMDEA water, Madrid, Spain
3
University of Massachusetts Amherst, Amherst, U.S.A.
Exocellular Electron Transfer (EET) in bacteria of the genus
Geobacter has been proved to be responsible of Fe-oxides reduction,
uranium bioremediaton or microbial electricity production. Previous
studies have shown that outermost membrane cytochromes are
responsible for establishing the electrical wiring from G. sulfurreducens
to the conducting surface. In this work, we combine electrochemical
techniques and metabolome analysis to elucidate the physiological aspects concerning EET in G. sulfurreducens. In order to mimic
the microbial response, steady-state cells of G. sulfureducens were
cultured in chemostats under either electron donor-limiting or TEAlimiting conditions with acetate as electron donor and fumarate as sole
electron acceptor. Electrochemical studies have revealed that a high
ratio electron donor-electron acceptor is enough for making EET a
constitutive process in Geobacter sulfurreducens even when culturing
the cells in absence of the insoluble Terminal Electron Acceptor (TEA).
OmcB, an outer-membrane cytochrome which actively participates in
electron transfer to Fe(III)-oxides and electrodes from microbial fuel
cells, showed one of the highest fold-change. Interestingly, the OmcB
knock-out strain was unpaired in the ability to transfer electrons to the
electrodes under TEA-limiting conditions, showing a similar response
than electron donor-limiting cells. The excess of carbon and electrons
seems to trigger a metabolic adaptation that includes electron transfer
mechanisms, such as the overexpression of the outer membrane
cytochrome omcB, among others. The integration of electrochemical techniques and metabolome analysis shows for the first time
how Geobacter species adapt their metabolic fluxes and outermost
cytochrome network to convert planktonic cells in ready-to-go electricity producing bacteria.