Effects of Oxygen Levels on the Transcription of nif and gln Genes in Bradyrhizobium japonicum

Abstract

The transciption of genes that function in N2 fixation (nif) and nitrogen assimilation (gln11) in Bradyrhizobiurn japonicum is coordinately induced in response to O2 limitation as well as symbiotic development. We have determined the relative steady-state mRN A levels for the nzfH, nfDK and glnll transcription units in bradyrhizobial cells grown under a variety of levels of aerobiosis and in cells isolated from soybean root nodules. All three transcripts are found in cells grown in a rich medium sparged with O2 concentrations of 5 % (v/v) or less. This expression is qualitatively similar to that observed for Bradyrhizobium during symbiotic development. Potential physiological mechanisms for the coordinate control of these genes are discussed.

Dissociation by NH4Cl treatment of the enzymic activities of glutamine synthetase II from Rhizobium leguminosarum biovar viceae

“…A post-transcriptional control was suggested by Adams & Chelm (1988) to explain the finding of the presence of GSII transcript in the absence of GSII transferase activity in N,-fixing bacteroids or free living microaerobic B. japonicum (Rao et al, 1978). We believe it is likely that GSII activity in bacteroids is modified by a mechanism similar to that reported in Fig.…”

Rhizobium meliloti 1021 has three differentially regulated loci involved in glutamine biosynthesis, none of which is essential for symbiotic nitrogen fixation

“…TnS mutations at the beginning of the locus (A and B, Fig. 1C) (14,41), as well as to the oxygen concentration (1,14,51). ginA (GSI) gene expression in B. japonicum (1, 10) and A. tumefaciens (56,57) appears to be constitutive.…”

“…Sixty pFB616::TnS plasmids were screened for their Gln phenotype in E. coli FDB213, and seven insertions were identified which resulted in a Gln-phenotype, all of which mapped 1 (Fig. 1C), which complemented the Gln-phenotypes of E. coli YMC11 and FDB213 as efficiently as did pFB54, which carries the K. pneumoniae glnA gene.…”

Bradyrhizobium japonicum glnB, a putative nitrogen-regulatory gene, is regulated by NtrC at tandem promoters

“…Transcript levels were quantitated by the S1 nuclease protection method adapted from Berk and Sharp (9) and described previously (2) in which mRNA transcribed from glnA and glnB could be detected in a single reaction. Approximately 5 ,ug of total cellular RNA was used per lane.…”

“…Expression of nitrogen assimilation capacity in B. japonicum is coordinated by separate regulatory networks that respond to nitrogen or oxygen limitation (2,17,39). The network responsive to nitrogen status shares many features with Ntr control in members of the Enterobacteriaceae (26,36), and genes that have functional roles similar to those of the ntrC and ntrA genes of enteric bacteria have been characterized from several rhizobial species (39,44,50,51,54).…”