Biofuel Cells Select for Microbial Consortia That Self-Mediate Electron Transfer

Abstract

Microbial fuel cells hold great promise as a sustainable biotechnological solution to future energy needs. Current efforts to improve the efficiency of such fuel cells are limited by the lack of knowledge about the microbial ecology of these systems. The purposes of this study were (i) to elucidate whether a bacterial community, either suspended or attached to an electrode, can evolve in a microbial fuel cell to bring about higher power output, and (ii) to identify species responsible for the electricity generation. Enrichment by repeated transfer of a bacterial consortium harvested from the anode compartment of a biofuel cell in which glucose was used increased the output from an initial level of 0.6 W m ؊2 of electrode surface to a maximal level of 4.31 W m ؊2 (664 mV, 30.9 mA) when plain graphite electrodes were used. This result was obtained with an average loading rate of 1 g of glucose liter؊1 day ؊1 and corresponded to 81% efficiency for electron transfer from glucose to electricity. Cyclic voltammetry indicated that the enhanced microbial consortium had either membrane-bound or excreted redox components that were not initially detected in the community. Dominant species of the enhanced culture were identified by denaturing gradient gel electrophoresis and culturing. The community consisted mainly of facultative anaerobic bacteria, such as Alcaligenes faecalis and Enterococcus gallinarum, which are capable of hydrogen production. Pseudomonas aeruginosa and other Pseudomonas species were also isolated. For several isolates, electrochemical activity was mainly due to excreted redox mediators, and one of these mediators, pyocyanin produced by P. aeruginosa, could be characterized. Overall, the enrichment procedure, irrespective of whether only attached or suspended bacteria were examined, selected for organisms capable of mediating the electron transfer either by direct bacterial transfer or by excretion of redox components.Biological fuel cells are a potential green energy technology. In a microbial fuel cell bacteria do not directly transfer the electrons which they produce to their characteristic terminal electron acceptor; instead, these electrons are diverted toward an electrode (anode). The electrons are subsequently conducted over a resistance or power user toward a cathode, and thus, bacterial energy is directly converted to electrical energy (35). Three main types of biofuel cells can be distinguished: photoautotrophic-type biofuel cells (38), more common heterotrophic-type biofuel cells, (9) and sediment biofuel cells (3). Biofuel cells have some characteristics that are similar to those of traditional power sources, as well as to those of anaerobic reactors. They can be described on the one hand by electrochemical parameters, such as power density (in watts per square meter of electrode surface), current output, and cell voltage, and on the other hand by biological parameters, such as the nutrient loading rate and biological/chemical oxygen demand (in kilograms per cubic meter per day) (34). Howev...

Renewable sustainable biocatalyzed electricity production in a photosynthetic algal microbial fuel cell (PAMFC)

“…Cyclic voltammetry revealed that redoxactive species were present in the anolyte medium with peaks within the operative anode potential of PAMFC 2. These kinds of peaks indicate the presence of electron shuttles (Rabaey et al 2004), which can result in current production. Further research will have to be conducted to reveal the mechanisms of chemical energy transfer from the algae to the microbial fuel cell.…”

The direct electrocatalysis of phenazine-1-carboxylic acid excreted by Pseudomonas alcaliphila under alkaline condition in microbial fuel cells

“…To date, many exoelectrogens have been employed in MFCs, including Shewanella putrefaciens (Kim et al, 1999), Geobacter sulfurreducens (G. sulfurreducens) (Bond and Lovley, 2003), Rhodoferax ferrireducens (Chaudhuri and Lovley, 2003), Klebsiella pneumoniae (K. pneumoniae) (Zhang et al, 2008), etc. These exoelectrogens, which are all cultivated in MFCs under neutral pH conditions, primarily depend on four mechanisms of electron transfer from fuels to electrodes, including membrane-bound cytochromes (Bond and Lovley, 2003;Bouhenni et al, 2010;Zhang et al, 2008), conductive bacterial pili (Gorby et al, 2006;Reguera et al, 2006), oxidation of reduced secondary metabolites (Zhuang et al, 2010a) or soluble redox mediators (Bond and Lovley, 2005;Rabaey et al, 2004;Wang et al, 2007). Furthermore, previous literatures have proved that flavin (Marsili et al, 2008), 2-amino-3-carboxy-1,4-naphthoquinon (Freguia et al, 2009) and 2,6-di-tert-butyl-p-benzoquinone (Deng et al, 2010) could be excreted by Pseudomonas aeruginosa (P. aeruginosa), Lactococcus lactis, K. pneumoniae, respectively, facilitating electron transfer in MFCs.…”

Whey as a substrate for generation of bioelectricity in microbial fuel cell using E.coli

“…A group of researchers substantiated the unnecessary action of exogenous electron mediators adding to a culture in MFCs (Jang et al, 2004;Rabaey et al, 2004;Rabaey et al, 2005b). These self-produced mediators, such as pyocyanin that is elicited by Pseudomonas aeruginosa, are able to transfer emancipated electrons to an electrode and produce bioelectricity in MFCs (Rabaey et al, 2004). Such compounds also exhibit the characterization of antibiotics.…”

“…Electrons produced by the bacteria are conveyed to the anode electrode and flow to the cathode ones linked by a conductive material containing a resistor or operated under a load. Electrons are able to be transferred to the anode by mediators, shuttles (Rabaey et al, 2004;Rabaey et al, 2005a) and nanowires (Beveridge, 2004;Reguera et al, 2005). Some Chemical mediators, such as neutral red , anthraquinone-2-6, disulfonate (AQDS), thionin, potassium ferricyanide (Bond et al, 2002) and methyl viologen (Logan, 2004) were used to increase the efficiency of power generation in MFCs.…”