Regulation of nitrite resistance of the cytochrome cbb3 oxidase by cytochrome c ScyA in Shewanella oneidensis

Abstract

Cytochrome c proteins, as enzymes to exchange electrons with substrates or as pure electron carriers to shuttle electrons, play vital roles in bacterial respiration and photosynthesis. In Shewanella oneidensis, a research model for the respiratory diversity, at least 42 c-type cytochromes are predicted to be encoded in the genome and are regarded to be the foundation of its highly branched electron transport pathways. However, only a small number of c-type cytochromes have been extensively studied. In this study, we identify soluble cytochrome c ScyA as an important factor influencing the nitrite resistance of a strain devoid of the bd oxidase by utilizing a newly developed transposon mutagenesis vector, which enables overexpression of the gene(s) downstream of the insertion site. We show that when in overabundance ScyA facilitates growth against nitrite inhibition by enhancing nitrite resistance of the cbb3 oxidase. Based on the data presented in this study, we suggest two possible mechanisms underlying the observed effect of ScyA: (1) ScyA increases electron flow to the cbb3 oxidase; (2) ScyA promotes nitrite resistance of the cbb3 oxidase, possibly by direct interaction. When in overabundance, small soluble cytochrome c ScyA enhances nitrite resistance of the cbb3 oxidase, facilitating growth against nitrite inhibition in the absence of the bd oxidase. Based on the data presented in this study, we suggest two possible underlying mechanisms, (1) that the anti-nitrite effect may be attributed to electron transfer; (2) that ScyA promotes nitrite resistance of the oxidase, possibly by direct interaction.