Suzanne Read (2010). MICROBIAL ECOLOGY OF EXTRACELLULAR ELECTRON TRANSFER PhD Thesis, School of Chemical Engineering, The University of Queensland.

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Author Suzanne Read
School, Centre or Institute School of Chemical Engineering
Institution The University of Queensland
Publication date 2010-05
Thesis type PhD Thesis
Supervisor Dr Korneel Rabaey
Philip Bond
Keller, Jurg
Total pages 195
Total colour pages 25
Total black and white pages 170
Subjects 09 Engineering
Abstract/Summary Bioelectrochemical Systems (BESs) use bacteria as catalysts for oxidation and/or reduction reactions at electrodes. The best known example of this phenomenon is the microbial fuel cell (MFC) where bacteria aid in the production of net power (e.g. wastewater systems). The bacterial catalysis is achieved through extracellular electron transfer (EET), a process allowing the transfer of electrons from the bacterial cell to the surface of an insoluble conductive material. While the present knowledge on EET is centred around two Gram-negative (GN) model systems, i.e. Shewanella and Geobacter species, populations on BES anodes are often dominated by other organisms, such as Gram-positive (GP) organisms or Pseudomonas species. Although studies have explored pure culture bacterial systems in MFCs and elucidated possible genetic pathways implicated in EET mechanisms, there is little genetic information available in co-culture systems. The purpose of this study was to obtain whole genome transcripts of these non-model organisms, to allow a better understanding on their possible EET mechanisms. Using whole genome mRNA microarrays on both GP (Clostridium acetobutylicum (C. acetobutylicum) and Enterococcus faecium (E. faecium)) and GN (Pseudomonas aeruginosa (P. aeruginosa) and Shewanella oneidensis (S. oneidensis)) bacteria in an active BES, we have identified a range of genes implicated in EET towards electrodes. In the pure culture study genes involved in energy production and conversion, cell wall/membrane biogenesis, intracellular trafficking and secretion were modulated in both the GN and GP results. Our results demonstrated that GPs display a low number of differentially expressed genes and maintain low current production relative to GNs. This implies that the GPs by themselves may not have a competent EET mechanism like the GNs. To further understand co-culture systems and their role in EET mechanisms we cultured E. faecium with either Geobacter sulfurreducens (G. sulfurreducens), S. oneidensis or P. aeruginosa. The co-culture transcripts revealed a number of genes that may be implicated in EET mechanisms including those involved in intracellular trafficking and secretion, stress, colicin production, defence mechanisms, cell adhesion, and sortase. More specifically, there seemed to be continual conflict between G. sulfurreducens and E. faecium while the other two co-cultures appeared to have reached some sort of equilibrium. Furthermore, within the co-culture system we observed a 30-70% increase in current production compared to the pure cultures as well as biofilm segregation. The GNs remained on top of the biofilm while E. faecium initially dominated the electrode biofilm. This indicated that the GP E. faecium could colonise the electrode faster and was consequently a major structural part of the biofilm. Additionally, the mechanism behind the increased current generation appears to be different within each co-culture. Interestingly, there is no evidence of the already known EET mechanisms as observed in this current and other previous pure culture studies.
Additional Notes colour-10,16,21,22,30,39,50,57,73,74,80,81,83,88,91,104,115,120,128, 135,152,160,161,162,166. Landscape- 20-22,50,73,79-81,84,96-99,104,113,120-128,140-142,147-150,154

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Created: Fri, 19 Nov 2010, 20:10:35 EST by Suzanne Read on behalf of Library - Information Access Service