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

Abstract

Sensing potential nitrogen-containing respiratory substrates such as nitrate, nitrite, hydroxylamine, nitric oxide (NO) or nitrous oxide (N2 O) 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), cytochrome c nitrite reductase (Nrf) and cytochrome c N2 O reductase (cNos) was investigated in cells of the Epsilonproteobacterium Wolinella succinogenes grown either by fumarate, nitrate or N2 O respiration. Furthermore, fumarate respiration in the presence of various nitrogen compounds or NO-releasing chemicals was examined. Upregulation of each of the Nap, Nrf and cNos enzyme systems was found in response to the presence of nitrate, NO-releasers or N2 O, and the cells were shown to employ three transcription regulators of the Crp-Fnr superfamily (homologues of Campylobacter jejuni NssR), designated NssA, NssB and NssC, to mediate the upregulation of Nap, Nrf and cNos. Analysis of single nss mutants revealed that NssA controls production of the Nap and Nrf systems in fumarate-grown cells, while NssB was required to induce the Nap, Nrf and cNos systems specifically in response to NO-generators. NssC was indispensable for cNos production under any tested condition. The data indicate dedicated signal transduction routes responsive to nitrate, NO and N2 O and imply the presence of an N2 O-sensing mechanism.

Nitrous Oxide Reduction Kinetics Distinguish Bacteria Harboring Clade I NosZ from Those Harboring Clade II NosZ

“…Growth yield is a measure of metabolic efficiency (40), and higher growth yields indicate tight coupling between catabolism and energy conservation. A mechanistic understanding about the differences in electron transfer and energy conservation between clade I NosZ and clade II NosZ is lacking, and detailed structural studies are warranted to explain the observed growth yield differences (15,23,41,42). Organisms with more efficient energy conservation mechanisms can direct a greater fraction of electrons toward biomass synthesis (i.e., increased f s ), which provides a competitive advantage, particularly in oligotrophic environments.…”

Nitrous Oxide Metabolism in Nitrate-Reducing Bacteria

“…In these cases, NO reduction to N 2 O is thought to serve predominantly in NO detoxification. In the light of such an N 2 O-producing capacity, it is not surprising that some nitrate ammonifiers such as W. succinogenes, A. dehalogenans and B. vireti have been reported to grow by anaerobic N 2 O respiration using N 2 O as sole electron acceptor (Kern & Simon, 2016;Mania, Heylen, van Spanning, & Frostegard, 2016;Sanford et al, 2012;Yoshinari, 1980). Moreover, the cells of some other species have been reported to reduce N 2 O and many genomes of ammonifiers indeed contain a nos gene cluster (see Section 2.2.2).…”

“…However, only recently a corresponding growth curve for W. succinogenes has been provided that allowed determination of a doubling time of 1.2 h and an estimate for growth yield of about 10 g dry cells per mole formate (Kern & Simon, 2016). Interestingly, this value is higher than the reported maximal cell yield of fumarate respiration (8.5 g of dry cells per mole formate; Bronder, Mell, Stupperich, & Kroger, 1982) as well as of nitrate and nitrite respiration (5.6 and 5.3 g of dry cells per mole formate, respectively) (Bokranz, Katz, Schr€ oder, Robertson, & Kr€ oger, 1983).…”

“…(SNP), S-nitrosoglutathione (GSNO) and spermine NONOate or N 2 O, but not to nitrite or hydroxylamine (Kern & Simon, 2016;Kern, Winkler, & Simon, 2011). However, nitrate-responsive two-component systems homologous to NarXL/NarQP from E. coli and other enteric bacteria are not encoded in the W. succinogenes genome.…”

“…Instead, this bacterium employs three transcription regulators of the Crp/FNR superfamily (homologs of C. jejuni NssR (nitrosative stress-sensing regulator) Elvers et al, 2005), designated NssA, NssB and NssC, to mediate upregulation of Nap, Nrf and cNos via dedicated signal transduction routes ( Fig. 6; Kern & Simon, 2016). Analysis of single nss mutants revealed that NssA controls production of the Nap and Nrf systems in fumarate-grown cells, while NssB was required to induce the Nap, Nrf and cNos systems specifically in response to NO-generators (Fig.…”