Quantitative proteomic analysis of the exoelectrogenic bacterium Arcobacter butzleri ED-1 reveals increased abundance of a flagellin protein under anaerobic growth on an insoluble electrode.

Exoelectrogens have the ability to generate electricity in mediator-less microbial fuel cells (MFCs) by extracellular electron transfer to the anode. We investigate the anode-specific responses of Arcobacter butzleri ED-1, the first identified exoelectrogenic Epsilonproteobacterium. iTRAQ and 2D-LC MS/MS driven proteomics were used to compare protein abundances in A. butzleri ED-1 when generating an electronegative potential (-225 mV) in an anaerobic half-cell - either growing as an electrogenic biofilm or suspended in the liquid medium - versus a microaerobic culture. This is the first quantitative proteomic study concentrating on growth of an exoelectrogen during current generation. From 720 proteins identified and quantified (soluble and insoluble sub-proteomes), statistical analysis reveals 75 differentially-expressed proteins. This dataset was enriched in proteins regulating energy and intermediary metabolism, electron and protein transport. Flagellin up-regulation was concomitant with electron transport in the anodic cells, while decreased abundance of a methyl-accepting chemotaxis protein suggested that flagella were involved in communication with the anode surface and electrogenesis, rather than motility. Two novel cytochromes potentially related to electron transport were up-regulated in anaerobic cultures. We demonstrate that employing an insoluble extracellular electron acceptor for anaerobic growth regulates multiple proteins involved in cell surface properties, electron transport and the methylcitrate cycle.