Escherichia coliknock-out mutants with altered electron transfer activity in the Micredox® assay and in microbial fuel cells

Electron transfer from bacteria to external electron acceptors is a biologically important phenomenon that is increasingly being harnessed as useful technology such as in the Micredox® assay and in microbial fuel cells (MFCs). Optimisation of these systems is limited by incomplete knowledge of the underlying genetics of electron transfer. The Keio collection of single gene knock-out Escherichia coli strains is being tested to find genes involved in electron transfer from bacteria to external electron acceptors. Initially, 21 E. coli strains from the Keio collection were selected and tested for altered electro-activity using the Micredox® assay. The Micredox® assay provides a rapid measurement of electron transfer from cells to a soluble electron acceptor (potassium hexacyanoferrate(III)) and was previously developed as a general test for BOD and toxicant measurement. Of the 21 Keio strains, 10 were found to have significantly reduced electron transfer and two were found to have significantly increased electron transfer. The mutant with the lowest electron transfer rate (nuoA) and the highest electron transfer rate (arcA) were then tested for electron transfer in microbial fuel cells (MFCs). The arcA mutant had slightly higher electron transfer rates than the wild type in mediator-less MFC while the nuoA mutant strain had very similar electro-activity to the wild type. However, in a mediated MFC, the mutants were consistently different from the wild type. These results demonstrate that single gene deletion strains of E. coli can have significantly altered electron transfer capabilities, both in the Micredox® assay and in MFCs. Importantly, the Micredox® assay was found to be a rapid and easily scaled-up method to discover genes that are important in electron transfer.