Extracellular Electron Transfer: Respiratory or nutrient homeostasis?

Exoelectrogens are able to transfer electrons extracellularly, enabling them to respire on insoluble terminal electron acceptors. Extensively studied exoelectrogens like Geobacter sulfurreducens and Shewanella oneindensis are Gram-negative, but more recently it has been reported that Gram-positive bacteria like Listeria monocytogenes and Enterococcus faecalis also exhibit the ability to transfer electrons extracellularly, although it is yet unclear whether this has a function in respiration or in redox control of the environment, for instance by reducing ferric iron for iron uptake. In the current issue of Journal of Bacteriology, Hederstedt, Gorton and Pankratova report on experiments that directly compare extracellular electron transfer (EET) pathways for ferric iron reduction and respiration and find a clear difference, providing further insights and new questions into the function and metabolic pathways of EET in Gram-positives.