It is likely that, similar to earlier biofilm studies, metabolic cooperation leads to increased performance [34], further research on this is warranted. The tower development by the G- organisms in coculture may be an ecological strategy to gain greater access to the carbon source, MM-102 mw while maintaining contact with the electrode via a superior electron transfer mechanism. The competition for substrate does not exclude a simultaneous metabolic cooperation for electron transfer. Hansen et al.,

[35] studied the evolution of species within a co-culture and described a MK-0457 solubility dmso symbiotic relationship which in a short duration apparently stabilized species interactions and affected community function. Spatial structure was the key environmental factor provided in our current study as well as in the Hansen study mentioned above. Given suitable conditions to establish a community, the co-cultures used in this study have been allowed to evolve and form their own GSK1120212 structure and interactions, which have produced a more productive community. Conclusion This study has shown that biofilms

of pure culture G- and G+ remain viable closest to the electrode while becoming non-viable on top or the further away from the electrode. This result was also reiterated by the reverse experiment, where a soluble electron acceptor was offered, with the top of the biofilm remaining viable and the bottom of the biofilm becoming non-viable. The G- cultures developed thicker biofilms, higher towers and produced higher current while the G+ produced thinner biofilms, smaller towers and lower current. Co-culture experiments between E. faecium MRIP and G- bacteria evidenced

a significant increase in current generation when grown together in the MFC, indicating a synergistic or mutualistic relationship between E. faecium and G- bacteria within this system which warrants further investigation. Methods Pure cultures and media Pure cultures used were G. sulfurreducens (ATCC 51573), P. aeruginosa PAO1, S. oneidensis MR-1, C. acetobutylicum (DSMZ 792) and E. faecium. These cultures were all grown in a media containing 0.5 g/L NaCl, 0.1 g/L KCl, 0.2 g/L NH4Cl, 0.465 g/L MgSO4, 1 ml/L CaCl2, 2 g/L NaHCO3, 6 g/L Na2HPO4, 3 g/L KH2PO4, 0.05 g/L yeast extract, 10 ml/L vitamin solution (Sigma-Aldrich Pty. Ltd., Castle Hill, Australia), 10 ml/L of trace element solution [36], 20 mM of sodium acetate (Sigma) and 20 mM lactate (Sigma). For the experiments in which the anode was not conveying any current (open circuit), 20 mM nitrate and 40 mM fumarate were supplied as electron acceptors. The catholyte was a 100 mM solution of potassium ferricyanide (K3 [Fe (CN)6]. Cultures were pre-grown to mid exponential phase (determined by OD 600 nm measurement) in the same media using soluble electron acceptors (nitrate and fumarate).