Revealing electron transfer in current-producing bacteria

Bhavin Siritanaratkul is a guest web-writer for EES. Bhavin is a PhD student in Inorganic Chemistry at Oxford, under the supervision of Prof. Fraser Armstrong. In his spare time, he enjoys playing the piano and reading science fiction.

Researchers from Japan and the USA have found the first clue to the electron transfer mechanism in a species of current-producing bacteria.

Some bacteria can generate electrical energy from its metabolic systems, and they are used in microbial fuel cells and bioremediation processes. Geobacter sulfurreducens is the most efficient current-producing bacteria found so far, but there is no conclusive mechanism for electron transfer from the bacteria to the electrode.

In this paper, Ryuhei Nakamura et al. the authors identify self-secreted flavin as the electron shuttle involved in this extracellular electron transfer (EET). For this bacteria, free-floating flavin in the solution does not contribute to EET, as changing the solution to a fresh one did not impact current production. Instead, electron transfer occurs through flavin bound to c-type cytochromes (c-Cyts) on the outer membrane.

The authors confirmed flavin secretion by spectroscopy and mass chromatography, and voltammetry showed that current production was influenced by the amount of flavin present. The importance of c-Cyts was revealed by a mutant comparison experiment, in which a mutant lacking several major c-Cyts produced less current than the wild type.

Extracellular electron transfer (EET) is a key step in current production from bacteria, and understanding the mechanisms involved can lead to optimization of microbial fuel cells.

by Bhavin Siritanaratkul

For more information read this Energy & Environmental Science article:

Uptake of self-secreted flavins as bound cofactors for extracellular electron transfer in Geobacter species
Akihiro Okamoto, Koichiro Saito, Kengo Inoue, Kenneth H. Nealson, Kazuhito Hashimoto and Ryuhei Nakamura
DOI: 10.1039/C3EE43674H

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