A novel two-component system of Bradyrhizobium japonicum:: ElmS and ElmR are encoded in diverse orientations

By completely sequencing the Bradyrhizobium japonicum insert of cosmid C27, a pair of genes was identified which was found to be highly similar to prokaryotic two-component systems. The genes of the putative regulator protein (214 aa), elmR, and the putative sensor histidine kinase (470 aa), elmS, are divergently oriented with their putative translational start sites separated by only 85 nucleotides. This new locus is located about 10 kb upstream of the sipS signal peptidase allele. The highest similarities were found to regulatory proteins of methylotrophic bacteria. Genetically defined B. japonicum mutants were tested for their growth on different monocarbon compounds and for the symbiotic interactions with soybeans. Because no obvious phenotype could be observed the functional importance of this sensor/regulator-pair remains to be determined.