Molecular characterization of nosRZDFYLX genes coding for denitrifying nitrous oxide reductase of Bradyrhizobium japonicum

The nosRZDFYLX gene cluster for the respiratory nitrous oxide reductase from Bradyrhizobium japonicum strain USDA110 has been cloned and sequenced. Seven protein coding regions corresponding to nosR, nosZ, the structural gene, nosD, nosF, nosY, nosL, and nosX were detected. The deduced amino acid sequence exhibited a high degree of similarity to other nitrous oxide reductases from various sources. The NosZ protein included a signal peptide for protein export. Mutant strains carrying either a nosZ or a nosR mutation accumulated nitrous oxide when cultured microaerobically in the presence of nitrate. Maximal expression of a PnosZ-lacZ fusion in strain USDA110 required simultaneously both low level oxygen conditions and the presence of nitrate. Microaerobic activation of the fusion required FixLJ and FixK2.