Growth during electricity production by Shewanella 33 Fig. 3. Confocal (a, c) and SEM (b, d) pictures of the bioﬁlm growing on anodes of fuel cells inoculated with Shewanella oneidensis MR-1. Fuel cells were fed with FW medium supplemented with lactate and (a, b) amino acids; (c, d) yeast extract. Anodes for CLSM examination were directly stained with the BacLight Live/Dead kit (Korber et al., 1996). Live cells appear green and dead cells red. Geothrix fermentans, which produces an electron shuttle (Nevin & Lovley, 2002a, b) remains afﬁxed to the anode surface in microbial fuel cells (Bond & Lovley, 2005). Incomplete oxidation of lactate to acetate coupled to electron transfer to electrodes similar to that reported here for S. oneidensis, was observed previously in Geothrix fermentans (Bond & Lovley, 2005). However, G. fermentans subsequently oxidized the acetate whereas S. oneidensis cannot. This is an important consideration because this means that only a third of the electrons available in the initial fuel is converted to electricity. Although the ability of Shewanella species to produce electricity from lactate has been noted many times (Kim et al., 1999a, b, 1999, 2002; Ringeisen et al., 2006; Bifﬁnger et al., 2007; Cho & Ellington, 2007), the results presented FEMS Microbiol Lett 278 (2008) 29–35 here demonstrate for the ﬁrst time that a substantial proportion of the electrons derived from lactate oxidation by S. oneidensis can be recovered as electrons in a microbial fuel cell. This is an important consideration because electron recoveries of o1% (Kim et al., 2002) and 10% (Ringeisen et al., 2006), are difﬁcult to reconcile with the concept that Shewanella species may use electrodes as a respiratory electron acceptor. The possibility of producing electricity with microbial cultures has been known for a long time, the study of self- sustaining microbial fuel cells in which microorganisms, known as electricigens, conserve energy to support growth from electron transfer to electrodes is in its infancy (Lovley, 2006). To date, each pure culture study with electricigens has demonstrated that the particular organism under c 2007 The Authors Journal compilation c 2007 Federation of European Microbiological Societies Published by Blackwell Publishing Ltd.