1. ¹The Advanced Wastewater Management Centre, University of Queensland, Brisbane, Queensland, Australia
2. ²Laboratory of Microbial Ecology and Technology (LabMET), University of Ghent, Ghent, Belgium
3. ³School of Medicine, University of Southern California, Los Angeles, CA, USA
4. ⁴Department of Earth Sciences, University of Southern California, Los Angeles, CA, USA

Correspondence: Dr K Rabaey, The Advanced Wastewater Management Centre, Gehrmann Building (60), The University of Queensland, Brisbane, Queensland 4072, Australia. E-mail: k.rabaey@uq.edu.au

Received 19 February 2007; Accepted 21 February 2007.

Abstract

Bio-electrochemical systems (BESs) have recently emerged as an exciting technology. In a BES, bacteria interact with electrodes using electrons, which are either removed or supplied through an electrical circuit. The most-described type of BES is microbial fuel cells (MFCs), in which useful power is generated from electron donors as, for example, present in wastewater. This form of charge transport, known as extracellular electron transfer, was previously extensively described with respect to metals such as iron and manganese. The importance of these interactions in global biogeochemical cycles is essentially undisputed. A wide variety of bacteria can participate in extracellular electron transfer, and this phenomenon is far more widespread than previously thought. The use of BESs in diverse research projects is helping elucidate the mechanism by which bacteria shuttle electrons externally. New forms of interactions between bacteria have been discovered demonstrating how multiple populations within microbial communities can co-operate to achieve energy generation. New environmental processes that were difficult to observe or study previously can now be simulated and improved via BESs. Whereas pure culture studies make up the majority of the studies performed thus far, even greater contributions of BESs are expected to occur in natural environments and with mixed microbial communities. Owing to their versatility, unmatched level of control and capacity to sustain novel processes, BESs might well serve as the foundation of a new environmental biotechnology. While highlighting some of the major breakthroughs and addressing only recently obtained data, this review points out that despite rapid progress, many questions remain unanswered.