Three transcription regulators of the Nss family mediate the adaptive response induced by nitrate, nitric oxide or nitrous oxide inWolinella succinogenes

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Sensing potential nitrogen-containing respiratory substrates such as nitrate, nitrite, hydroxylamine, nitric oxide (NO) or nitrous oxide (N2O) in the environment and subsequent upregulation of corresponding catabolic enzymes is essential for many microbial cells. The molecular mechanisms of such adaptive responses are, however, highly diverse in different species. Here, induction of periplasmic nitrate reductase (Nap), cytochromecnitrite reductase (Nrf) and cytochromecN2O reductase (cNos) was investigated in cells of the EpsilonproteobacteriumWolinella succinogenesgrown either by fumarate, nitrate or N2O respiration. Furthermore, fumarate respiration in the presence of various nitrogen compounds or NO-releasing chemicals was examined. Upregulation of each of the Nap, Nrf andcNos enzyme systems was found in response to the presence of nitrate, NO-releasers or N2O, and the cells were shown to employ three transcription regulators of the Crp-Fnr superfamily (homologues ofCampylobacter jejuniNssR), designated NssA, NssB and NssC, to mediate the upregulation of Nap, Nrf andcNos. Analysis of singlenssmutants revealed that NssA controls production of the Nap and Nrf systems in fumarate-grown cells, while NssB was required to induce the Nap, Nrf andcNos systems specifically in response to NO-generators. NssC was indispensable forcNos production under any tested condition. The data indicate dedicated signal transduction routes responsive to nitrate, NO and N2O and imply the presence of an N2O-sensing mechanism.

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