Respiratory strategies in Geobacter sulfurreducens as revealed by ATR-SEIRAS

BERNÁ, ANTONIO; ESTEVE-NUÑEZ, ABRAHAM; BUSALMEN, JUAN PABLO; FELIU, JUAN MIGUEL

Nice

Simposio; 61st Annual Meeting of the International Society of Electrochemistry; 2010

Cytochromes located at the bacterial surface have been shown to be the molecules responsible for electron transport to solid acceptors in G. sulfurreducens 1, 2. It has been clearly documented using surface enhanced IR spectroscopy during electricity production from adsorbed bacteria on a polarized gold surface 1, 2. In those works performed with whole bacterial cells the enhanced sensitivity of the SEIRA effect allowed the identification of proteins at the cell surface as the electrode contacting molecules, while a differential analysis of oxidized-minus-reduced spectra revealed that electron transport to the electrode is directly related to the conformational change of external cytochromes upon redox transition. A more detailed analysis using SNIFTIRS modulation allowed the recognition of the IR fingerprint of the Geobacter surface 2. The same pool of techniques is used in this work together with the possibility to produce Geobacter sulfurreducens cultures of different physiology, to gain information about the unprecedented versatility of these bacteria to select and control its respiratory pathway in order to adapt to external constrains. Growing G. sulfurreducens in continuous culture reactors under electron donor limitation produced a phenotype with minimal electrochemical activity that did not present the typical redox transition corresponding to external cytochromes in the SNIFTIRS analysis. On the other hand, cells grown under electron acceptor limitation had a well defined redox signal under cyclic voltammetry, accompanied by the spectral changes due to cytochromes conformational transition. Spectroelectrochemical data were complemented with SDS-PAGE results showing markedly different profiles of outer membrane cytochromes, in which acceptor limited cells had higher amount and variety.  Results presented in this work provide new information that supports the success of Geobacter species in electrogenic biofilms and highlight the importance of environmental conditions in the implementation of electrogenic waste treatments.