Skip to main content
. Author manuscript; available in PMC: 2021 Oct 25.
Published in final edited form as: Cell Host Microbe. 2018 Nov 14;24(5):611–613. doi: 10.1016/j.chom.2018.10.018

Figure 1. Flavin EET Knowns and Unknowns.

Figure 1.

From the microbial perspective, accessing a terminal electron acceptor to power metabolism is a problem that transcends context. The flavin EET pathway has been elucidated as a specific solution that provides an advantage in the anaerobic intestinal tract for L. monocytogenes, whose natural ecological range is broad, encompassing soils to host-associated environments. These environments often contain complex microbial communities and diverse molecules that may influence EET metabolism. Light et al. (Light et al.,2018) propose that EET proceeds through an alternative membrane-bound electron transport chain to the outside of the cell. This electron transport chain consists of an NADH dehydrogenase (Ndh2), specific menaquinone derivatives (DMK), possibly two membrane proteins (EetA and EetB), and an outward facing lipoprotein (PplA) with covalently attached flavins that serve as electron carriers. Their experiments provide evidence that flavins are sufficient to serve as extracellular electron shuttles from PplA to iron(III) and electrodes, but many questions remain, e.g.: (1) what is the terminal electron acceptor in any given niche? (2) What EES are involved in long range electron transfer? (3) How does EET contribute to energy generation within the cell?