Molecular Underpinnings of Nitrite Effect on CymA-Dependent Respiration in Shewanella oneidensis

Abstract

Shewanella exhibit a remarkable versatility of respiration, with a diverse array of electron acceptors (EAs). In environments where these bacteria thrive, multiple EAs are usually present. However, we know little about strategies by which these EAs and their interaction affect ecophysiology of Shewanella. In this study, we demonstrate in the model strain, Shewanella oneidensis MR-1, that nitrite, not through nitric oxide to which it may convert, inhibits respiration of fumarate, and probably many other EAs whose reduction depends on quinol dehydrogenase CymA. This is achieved via the repression of cyclic adenosine monophosphate (cAMP) production, a second messenger required for activation of cAMP-receptor protein (Crp) which plays a primary role in regulation of respiration. If nitrite is not promptly removed, intracellular cAMP levels drop, and this impairs Crp activity. As a result, the production of nitrite reductase NrfA, CymA, and fumarate reductase FccA is substantially reduced. In contrast, nitrite can be simultaneously respired with trimethylamine N-oxide, resulting in enhanced biomass.

NapB in excess inhibits growth of Shewanella oneidensis by dissipating electrons of the quinol pool

“…1B), which encodes an enzyme dictating cAMP degradation; the cpdA mutant had substantially elevated cAMP levels31. These results are expected because nitrite inhibition can be relieved by increased cAMP intracellular levels, either by altering production/degradation or by adding the molecules exogenously24.…”

“…Nitrite inhibition of growth with fumarate is due to lowered intracellular cAMP levels in S. oneidensis 24. As multiple factors are involved in cAMP homeostasis3133, we reasoned that at least some in their altered abundance or absence may suppress nitrite inhibition.…”

“…1B). Given that the cyaC mutant is hypersensitive to nitrite242531, this observation suggests that the cyaC gene is overexpressed because of the transposon-borne promoter. In parallel, 6 suppressors had transposons that mapped within the promoter and coding sequence of the cpdA gene (Fig.…”

“…However, this is not the case in S. oneidensis given that nitrite is similarly effective in a NO-free environment2324. During aerobic growth of S. oneidensis , the primary target of nitrite is the cytochrome cbb 3 oxidase, the enzyme complex predominantly responsible for oxygen respiration25262728.…”

“…During aerobic growth of S. oneidensis , the primary target of nitrite is the cytochrome cbb 3 oxidase, the enzyme complex predominantly responsible for oxygen respiration25262728. When non-oxygen EAs are used to support growth, nitrite inhibits respiration of CymA-dependent but not -independent EAs24. This is achieved via repression of cyclic adenosine monophosphate (cAMP) production, a second messenger required for activation of cAMP-receptor protein (Crp).…”