Dynamic roles of inner membrane electron-transfer hub of Shewanella oneidensis MR-1 in response to extracellular reduction kinetics

Abstract

The unique extracellular electron transfer (EET) network of exoelectrogens endow them with extraordinary extracellular respiration ability to facilitate environmental remediation and biogeochemical processes. Shewanella oneidensis MR-1 is an environmentally ubiquitous exoelectrogen possessing multiple EET pathways. While the inner membrane CymA protein is widely believed to serve as an essential electron transfer hub in all these pathways, here our experimental evidences suggest another possibility: its EET role is highly dependent on extracellular reduction kinetics. Comparison of the bacterial EET and extracellular reduction performances in response to different species and concentrations of extracellular electron acceptors shows that the fraction of electron efflux contributed by the CymA pathway is positively correlated to the EET rate. This means some unknown EET pathways independent of CymA are activated under slow EET condition, likely as a strategy of self-adaption to environmental changes by feedback regulating the electron transport pathways. Our findings provide a new perspective to facilitate better understanding of the dynamic bacteria-environment interactions, and may inspire the discovery of new EET proteins and the development of more environmentally-robust biotechnologies for environmental remediation applications.