Microbial Consortia Engineering for Improved MFC Performance

Microbial fuel cells (MFCs) are bioelectrochemical devices that convert diverse organic and inorganic matter sources into electrical energy by exploiting the electron transferring capabilities of exoelectrogenic bacteria¹. In MFCs, the conventional bacterial transfer of electrons to natural redox partners or electron acceptors is replaced by the transfer of electrons directly to an electrode to produce electrical current. Although we have a good understanding of the physical and chemical characteristics of MFC design and operation, our understanding of the diverse metabolic processes associated with current generation remains limited ². Here we programmed an E. coli chassis with the essential genetic components required to perform enhanced current generation. To go beyond well-characterized pathways for electron transfer found in model exoelectrogenic bacteria such as Geobacter or Shewanella, we used functional metagenomics to search for genes facilitating electron transfer in environmental fosmid libraries hosted in EPI300â„¢-T1R E. coli. These libraries were derived from wastewater and hydrocarbon-degrading microbial communities as the conditions in these anaerobic environments potentially favour genes associated with enhanced current generation. We reasoned that by applying a selective pressure within the MFC milieu on pools of fosmids it would be possible to select for genes and pathways driving electron transfer under extended operating conditions. Metagenomic libraries were pooled and inoculated into dual-chamber MFCs fed with acetate or glucose. After several rounds of enrichment, MFCs showed significant increase in power output compared to unprogrammed E.coli controls. Selected pools were sequenced to identify metabolic processes enriched under MFC operation conditions using both whole genome shotgun metagenomic and metatranscriptomic approaches. Additionally, qPCR was performed on selected genes of interest to validate gene expression results. By combining the metagenomic data from the fosmid gene enrichments and their expression patterns, we aim to recover genes or gene cassettes crucial for enhanced extracellular electron transfer. Identified genes or gene cassettes will be used to engineer synthetic microbial consortia for increased performance in MFCs, as mixed communities generally perform better in MFC settings than pure cultures³. Compared to other methods to improve MFC performance, consortia and biofilm engineering have the potential to be significantly more cost-effective, and could be promising steps towards the widespread and accessible implementation of MFC technology as a renewable energy production strategy.

1. Logan, B. E. Exoelectrogenic bacteria that power microbial fuel cells. Nat. Rev. Microbiol. 7, 375–381 (2009).

2. Fedorovich, V. et al. Novel electrochemically active bacterium phylogenetically related to Arcobacter butzleri, isolated from a microbial fuel cell. Appl. Environ. Microbiol. 75, 7326–34 (2009).

3. Pham, T. H. et al. Metabolites produced by Pseudomonas sp. enable a Gram-positive bacterium to achieve extracellular electron transfer. Appl. Microbiol. Biotechnol. 77, 1119–1129 (2008).