Comparison of arcobacter butzleri ED-1 and arcobacter L anode biofilm formation and a proteomic comparison of A. butzleri ED-1 at the anode of a half microbial fuel cell
Knighton, Matthew Charles
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Microbial fuel cells (MFCs) are electrochemical devices that exploit the ability of certain microorganisms to anaerobically respire using an insoluble terminal electron acceptor and therefore generate an electrical current. These bacteria are called electrogens or electrogenic bacteria. Two species of Arcobacter, Arcobacter butzleri ED-1 and Arcobacter L were isolated from the anodic chamber of an acetate fed MFC, and A. butzleri ED-1 was found to be the more electrogenic of the two bacteria. Arcobacter spp. are proteobacteria and A. butzleri ED-1 and Arcobacter L were the first example of electrogenically active e proteobacteria. It was decided to study their interactions with the anode by fluorescent microscopy and study their electrogenic mechanisms by comparative proteomics using the iTRAQ method as it would allow for simultaneous identification and quantification of peptides in multiple samples. Fluorescent imaging over a period of 120 h in a half MFC showed that both A. butzleri ED-1 and Arcobacter L formed a thin anodic biofilm of a few cells thick and that A. butzleri ED-1 maintained a more stable anodic biofilm than Arcobacter L. iTRAQ analysis showed that the flagellin FlaA was up-regulated 2.4 fold at the anode but no other electron transport proteins or adhesins were upregulated. These results were distinct from those observed for other electrogenic bacteria (Geobacter sulfurreducens and Shewanella oneidensis MR-1) in previous studies which exhibited up-regulated electron transport proteins at the anode as well as forming an anodic biofilm of 50 μm thick. Therefore based on these results it was concluded that FlaA was most likely playing an important role A. butzleri ED-1 anode biofilm formation and that the mechanisms of electrogenesis in A. butzleri ED- 1 and Arcobacter L may be novel compared to those previously characterised. It was also concluded that one possible reason for A. butzleri ED-1 being more electrogenic than Arcobacter L was its ability to form a more stable anodic biofilm. It must be noted that both of these conclusions are highly speculative and further study is needed to elucidate the electrogenic mechanisms of A. butzleri ED-1 and to further compare biofilm formation between the two species.