A Cysteine Pair Controls Flavin Reduction by Extracellular Cytochromes during Anoxic/Oxic Environmental Transitions
Michael P. Norman, Marcus J. Edwards, Gaye F. White, Joshua A. J. Burton, Julea N. Butt, David J. Richardson, Ricardo O. Louro, Catarina M. Paquete, Thomas A. Clarke
Abstract
Bacteria that live at the oxic/anoxic interface have to rapidly adapt to changes in oxygen levels within their environment. The facultative anaerobe Shewanella oneidensis MR-1 can use EET to respire in the absence of oxygen, but on exposure to oxygen, EET could directly reduce extracellular oxygen and generate harmful reactive oxygen species that damage the bacterium. By modifying an extracellular cytochrome called MtrC, we show how preventing a redox-active disulfide from forming causes the production of cytotoxic concentrations of peroxide. The disulfide affects the affinity of MtrC for the redox-active flavin mononucleotide, which is part of the EET pathway. Our results demonstrate how a cysteine pair exposed on the surface controls the path of electron transfer, allowing facultative anaerobic bacteria to rapidly adapt to changes in oxygen concentration at the oxic/anoxic interface.