Immobilization of anode-attached microbes in a microbial fuel cell

Bioelectrochemical systems (BESs) are based on electron transfer between microbes and an electrode surface. Most investigations into the mechanisms of electron transfer from a microbe to an anode have focused on two microorganisms, Geobacter sulfurreducens (Marsili et al. 2008; Holmes et al. 2006; Strycharz et al. 2010; Inoue et al. 2010; Nevin et al. 2009; Srikanth et al. 2008) and Shewanella oneidensis (Bretschger et al. 2007; Gorby et al. 2006), where it has been shown that specific genes and proteins are involved in exogenous electron transfer. Further study of current-generating (exoelectrogenic) bacteria and biofilms will benefit from isolating and identifying other microorganisms that are capable of electron transfer to an electrode.Isolation techniques to identify novel exoelectrogens have typically involved dilution-to-extinction in BESs, or isolation on ferric iron agar plates. A U-tube reactor was developed (Zuo et al. 2008) that would allow a single microbe, obtained by serial dilutions, to deposit by sedimentation onto a flat anode surface. This technique was used to identify novel exoelectrogens Ochrobactrum anthropi YZ-1 (Zuo et al. 2008) and Enterobacter cloacae FR (Rezaei et al. 2009). However, the cumbersome process required many serial transfers to obtain these isolates. A microbe related to Clostridium butyricum was isolated from a microbial fuel cell (MFC) using ferric iron agar plates (Park et al. 2001), but this method of isolation does not target all exoelectrogens as some microbes have been isolated that can generate current but not reduce iron (Kim et al. 2004; Zuo et al. 2008).In addition to spread-plating techniques, screening of arrays of microorganisms on ferric iron agar plates is possible through printer technology (Ringeisen et al. 2009). This approach can be used to print very small droplets of a cell suspension diluted to contain single microbes. To take advantage of this technology, for example by printing single cells in a grid p