strain JR [30]. In some instances G+ have been seen to dominate populations in mixed culture MFCs [30, 31]. Hence, while G+ have some capacity for electron transfer, it is apparent that the G- used here generated

much greater CB-839 nmr current in our MFC conditions. Interestingly, the current generated by P. aeruginosa in batch mode was larger than in continuous mode which may be concomitant with the gradual loss of redox shuttles AZD3965 nmr previously implicated in electron transfer by P. aeruginosa [10]. P. aeruginosa as a pure culture decreased its current production after the 48 hour timepoint (Figure 4) in continuous mode, however, in batch mode it continued to increase current. Potentially, a gradual wash-out 4-Hydroxytamoxifen nmr of redox shuttles, which can be produced by P. aeruginosa, explains the lower performance in continuous mode [32]. A comprehensive, non-MFC based study using PA01 to investigate phenotypic differentiation and seeding dispersal also

noted a halt in biofilm height after about 48 hours [33]. During that study microcolonies of 80 μm diameter became differentiated, leaving the microcolony hollow by day 3. Similarly to our current study, by 48 hours PAO1 had formed 20 ± 4 μm thick biofilms, which did not increase throughout the duration of the experiment. Although the aforementioned study used different parameters, the growth and retardation of the PA01 biofilms coincided with the timing of the assumed decreased EET activity

in our MFC. Co-culture versus pure culture current generation The three co-cultures (with E. faecium) used in this study all generated more current together then when grown as pure cultures. Although this has not yet been investigated at a deeper level, several studies have noted the coexistence between G+ and G- within the MFC environment. For example, the role of a phenazine electron shuttle has been verified in an earlier MFC study where it was observed to increase current generation in co-cultures of Brevibacillus sp. and Enterococcus sp. with Pseudomonas sp. These for studies determined that the G+ were able to use electron shuttles (mediators) produced by Pseudomonas sp [10, 28], the combination of both bacteria being the more successful one. Whether other mechanisms such as quorum regulation or the establishment of a syntrophic association is in play is yet to be investigated. In a recent study, Nevin et al., [20] described how pure culture biofilms of G. sulfurreducens were able to reach current densities of the same order of magnitude as mixed population current densities. In the latter case, the anode surface was minimized in order to ensure that the anode became the limiting factor.