Bradyrhizobium japonicum FixK 2 , a Crucial Distributor in the FixLJ-Dependent Regulatory Cascade for Control of Genes Inducible by Low Oxygen Levels

Abstract

ABSTRACT Bradyrhizobium japonicum possesses a second fixK -like gene, fixK 2 , in addition to the previously identified fixK 1 gene. The expression of both genes depends in a hierarchical fashion on the low-oxygen-responsive two-component regulatory system FixLJ, whereby FixJ first activates fixK 2 , whose product then activates fixK 1 . While the target genes for control by FixK 1 are unknown, there is evidence for activation of the fixNOQP , fixGHIS , and rpoN 1 genes and some heme biosynthesis and nitrate respiration genes by FixK 2 . FixK 2 also regulates its own structural gene, directly or indirectly, in a negative way.