title: The nitrate-sensing NasST system regulates nitrous oxide reductase and periplasmic nitrate reductase in Bradyrhizobium japonicum.
abstract: The soybean endosymbiont Bradyrhizobium japonicum is able to scavenge the greenhouse gas N2O through the N2O reductase (Nos). In previous research, N2O emission from soybean rhizosphere was mitigated by B. japonicum Nos(++) strains (mutants with increased Nos activity). Here, we report the mechanism underlying the Nos(++) phenotype. Comparative analysis of Nos(++) mutant genomes showed that mutation of bll4572 resulted in Nos(++) phenotype. bll4572 encodes NasS, the nitrate (NO3(-))-sensor of the two-component NasST regulatory system. Transcriptional analyses of nosZ (encoding Nos) and other genes from the denitrification process in nasS and nasST mutants showed that, in the absence of NO3(-) , nasS mutation induces nosZ and nap (periplasmic nitrate reductase) via nasT. NO3(-) addition dissociated the NasS-NasT complex in vitro, suggesting the release of the activator NasT. Disruption of nasT led to a marked decrease in nosZ and nap transcription in cells incubated in the presence of NO3(-). Thus, although NasST is known to regulate the NO3(-)-mediated response of NO3(-) assimilation genes in bacteria, our results show that NasST regulates the NO3(-) -mediated response of nosZ and napE genes, from the dissimilatory denitrification pathway, in B. japonicum.
authors.affiliation: Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, 980-8577, Japan.
authors.forename: Cristina
authors.initials: C
authors.lastname: Sánchez
authors.forename: Manabu
authors.initials: M
authors.lastname: Itakura
authors.forename: Takashi
authors.initials: T
authors.lastname: Okubo
authors.forename: Takashi
authors.initials: T
authors.lastname: Matsumoto
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Yoshikawa
authors.forename: Aina
authors.initials: A
authors.lastname: Gotoh
authors.forename: Masafumi
authors.initials: M
authors.lastname: Hidaka
authors.forename: Takafumi
authors.initials: T
authors.lastname: Uchida
authors.forename: Kiwamu
authors.initials: K
authors.lastname: Minamisawa
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics*; D020369:Bradyrhizobium / Q000201:enzymology* / Q000235:genetics* / Q000378:metabolism; D058440:Denitrification; D015964:Gene Expression Regulation, Bacterial; D015971:Gene Expression Regulation, Enzymologic; D016680:Genome, Bacterial; D026901:Membrane Transport Proteins / Q000235:genetics; D009154:Mutation; D050901:Nitrate Reductase / Q000235:genetics*; D009566:Nitrates / Q000378:metabolism*; D010088:Oxidoreductases / Q000235:genetics* / Q000378:metabolism; D019897:Periplasm / Q000201:enzymology; D016601:RNA-Binding Proteins / Q000235:genetics; D058441:Rhizosphere; D013025:Glycine max / Q000382:microbiology
chemical_list: D001426:Bacterial Proteins; D026901:Membrane Transport Proteins; D009566:Nitrates; D016601:RNA-Binding Proteins; C064872:antiterminator proteins, Bacteria; D010088:Oxidoreductases; C022763:nitrous oxide reductase; D050901:Nitrate Reductase