Abstract
Respiration is a fundamental process that has to optimally respond to metabolic demand and environmental changes. We previously showed that nitrate respiration, crucial for gut colonization by enterobacteria, is controlled by polar clustering of the nitrate reductase increasing the electron flux through the complex. Here, we show that the formate dehydrogenase electron-donating complex, FdnGHI, also clusters at the cell poles under nitrate-respiring conditions. Its proximity to the nitrate reductase complex was confirmed by its identification in the interactome of the latter, which appears to be specific to the nitrate-respiring condition. Interestingly, we have identified a multiprotein complex dedicated to handle nitric oxide resulting from the enhanced activity of the electron transport chain terminated by nitrate reductase. We demonstrated that the cytoplasmic NADH-dependent nitrite reductase NirBD and the hybrid cluster protein Hcp are key contributors to regulation of the nitric oxide level during nitrate respiration. Thus, gathering of actors involved in respiration and NO homeostasis seems to be critical to balancing maximization of electron flux and the resulting toxicity.IMPORTANCE Most bacteria rely on the redox activity of respiratory complexes embedded in the cytoplasmic membrane to gain energy in the form of ATP and of an electrochemical gradient established across the membrane. Nevertheless, production of harmful and toxic nitric oxide by actively growing bacteria as either an intermediate or side-product of nitrate respiration challenges how homeostasis control is exerted. Here, we show that components of the nitrate electron transport chain are clustered, likely influencing the kinetics of the process. Nitric oxide production from this respiratory chain is controlled and handled through a multiprotein complex, including detoxifying systems. These findings point to an essential role of compartmentalization of respiratory components in bacterial cell growth.
Highlights
Respiration is a fundamental process that has to optimally respond to metabolic demand and environmental changes
The electron-donating respiratory complex, formate dehydrogenase encoded by the fdnGHI operon, is a good candidate owing to its similar transcriptional regulation [20]
The E. coli formate dehydrogenase complex is composed of three subunits and organized into a physiological trimer, (FdnGHI)3, with a cardiolipin molecule positioned at the trimer interface [23]
Summary
Respiration is a fundamental process that has to optimally respond to metabolic demand and environmental changes. Optimizing electron flux through clustering of nitrate reductase likely leads to nitrite accumulation and nitric oxide (NO) production Functioning of this electron transport chain in enteric bacteria such as E. coli and Salmonella enterica serovar Typhimurium is associated with NO production mainly resulting from the reduction of nitrite by nitrate reductase [12,13,14,15]. Among Hcp-dependent S-nitrosylated targets are the nitrate reductase complex, multiple metabolic enzymes, and the OxyR transcription factor whose S-nitrosylation entails a distinct nitrosative stress regulon [19] In this context, we questioned how efficiency of the nitrate respiratory chain is attained through polar clustering of the nitrate reductase complex and how NO homeostasis control is exerted
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