Microbial ecology meets electrochemistry: electricity-driven and driving communities

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.

A novel ecological role of the Firmicutes identified in thermophilic microbial fuel cells

“…Previous studies of MFCs inoculated with Firmicutes isolates only produced current in the presence of an exogenous electron shuttle (Rabaey et al, 2005(Rabaey et al, , 2007Milliken and May, 2007;Pham et al, 2008) or as a byproduct of glucose fermentation (Park, 2001;Kim et al, 2005). Therefore, it was recently concluded that the presence of Gram-positive bacteria in an MFC is an outcome of ecological interaction with Gram-negative electricity-producing organisms rather than a functional interaction and electron transfer with the electrode surface (Rabaey et al, 2007).…”

“…Although 16S rDNA sequences belonging to the Firmicutes have previously been detected in the anode communities of active fuel cells (Lee et al, 2003;Kim et al, 2004Kim et al, , 2006Rabaey et al, 2004Rabaey et al, , 2007Aelterman et al, 2006;Hamid Rismani-Yazdi et al, 2007;Mathis et al, 2007), there are a limited number of publications where Firmicutes represent a dominant portion (450%) of the anode community composition (Rabaey et al, 2004(Rabaey et al, , 2007Aelterman et al, 2006;Hamid Rismani-Yazdi et al, 2007;Mathis et al, 2007). Previous studies of MFCs inoculated with Firmicutes isolates only produced current in the presence of an exogenous electron shuttle (Rabaey et al, 2005(Rabaey et al, , 2007Milliken and May, 2007;Pham et al, 2008) or as a byproduct of glucose fermentation (Park, 2001;Kim et al, 2005). Therefore, it was recently concluded that the presence of Gram-positive bacteria in an MFC is an outcome of ecological interaction with Gram-negative electricity-producing organisms rather than a functional interaction and electron transfer with the electrode surface (Rabaey et al, 2007).…”

“…Additionally, the importance of synergistic activity in electrochemically active biofilms has been demonstrated in mesophilic MFCs. Here, electrochemically inactive isolates exploited the redox shuttle produced by electrochemically active isolates (Rabaey et al, 2005(Rabaey et al, , 2007Pham et al, 2008). It is plausible that bacteria like Geobacillus spp.…”

Microtoming coupled to microarray analysis to evaluate the spatial metabolic status of Geobacter sulfurreducens biofilms

“…A potential limitation on the metabolism for cells closer to the anode surface is lack of electron donor or nutrients due to cells in the outer section consuming these components (He et al, 2005;Marcus et al, 2007;Rabaey et al, 2007;Torres et al, 2008). G. sulfurreducens genes encoding acetate transporters that are more highly expressed when acetate is limiting have been identified (Risso et al, 2008).…”

New method for characterizing electron mediators in microbial systems using a thin-layer twin-working electrode cell

“…Arguably, mediator dependent electron transfer is the most common mode of electron transfer, where a wide range of bacteria accomplish extracellular electron transfer (EET) by producing various soluble electron shuttles or mediators (Rabaey et al, 2007).…”