Functional genomic analysis of global regulator NoIR in Sinorhizobium meliloti

NolR is a regulator of nodullation genes present in species belonging to the genera Rhizobium and Sinorhizobium. The expression of the nolR gene in Sinorhizobium meliloti AK631 was investigated in relation to stage of growth, availability of nutrients, and different environmental stimuli using the nolR::lacZ fusion report system. It has been shown that the nolR gene is regulated in a population-density-dependent fashion and influenced by a number of environmental stimuli, including nutrients, pH, and oxygen. Exploration of the physiological functions of NolR under various laboratory conditions has shown that NolR is, required for the optimal growth of the bacteria on solid media, optimal survival of the bacteria in carbon-starved minimal medium, and after heat shock challenge. NolR also is involved in recipient-induced conjugative transfer of a plasmid. Proteome analysis of strain AK631 and its Tn5-induced no/R-deficient mutant EK698 revealed that a functional NoIR induced significant differences in the accumulation of 20 polypeptides in peptide mass fingerprinting early-log-phase cultures and 48 pollypeptides in stationarY7phase cultures. NoIR acted mainly as a repressor in the early-log-phase cultures, whereas it acted as both repressor and activator in the stationaryphase cultures. The NoIR protein and 59 NoIR-associated proteins have been identified by peptide mass fingerprinting. The NolR protein was differentially expressed only in the NolR' wild-type strain AK631 but not in its NolR- derivative EK698, confirming that no functional NolR was produced in the mutant. The NolR-associated proteins have diverse functions in amino acid metabolism, carbohydrate metabolism, lipid metabolism, nucleotide metabolism, energy metabolism, metabolism of Co-factors, and cellular adaptation and transportation. These results further support our previous proposal that the NolR is a global regulatory protein which is required for the optimization of nodulation, bacterial growth and survival, and conjugative transfer of a plasmid.