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Abstract
In this work we report on the occurrence of at least two different redox pairs on
the cell surface of the electrogenic bacteria Geobacter sulfurreducens adsorbed on
gold that are expressed in response to the polarization potential. As previously reported
on graphite (Environ. Sci. Technol. 42 (2008) 2445) a typical low potential redox
pair is found centered at around -0.06 V when cells are polarized for a few hours
at 0.2 V, while a new pair centered at around 0.38 V is expressed upon polarization
at 0.6 V. Reversible changes in the IR band pattern of whole cells where obtained
by Attenuated Total Reflection-Surface Enhanced Infrared Absorption Spectroscopy (ATR-SEIRAS)
upon potential cycling around both redox pairs. Changes clearly resemble the electrochemical
turnover of oxidized/reduced states in c-type cytochromes, thus evidencing the nature
of the involved molecules. The expression of external cytochromes in response to the
potential of the electron acceptor suggests the existence of alternative pathways
of electron transport with different energy yield, though it remains to be demonstrated.
2009 Elsevier B.V. All rights reserved.