Isolation and Regulation of Sinorhizobium meliloti 1021 Loci Induced by Oxygen Limitation

Eleven Sinorhizobium meliloti 1021 loci whose expression was induced under low oxygen concentrations were identified in a collection of 5,000 strains carrying Tn5-1063 (luxAB) transcriptional reporter gene fusions. The 11 Tn5-1063-tagged loci were cloned and characterized. The dependence of the expression of the tagged loci on the FixL/FixJ oxygen-sensing two-component regulatory system was examined. Three of the loci were found to be dependent upon fixL and fixJ for their expression, while one locus showed a partial dependence. The remaining seven loci showed fixL- and fixJ-independent induction of expression in response to oxygen limitation. This suggests that in S. meliloti, additional regulatory system(s) exist that respond either directly or indirectly to oxygen limitation conditions.