[LPS mutants of Sinorhizobium meliloti and their nodulation competitiveness].

Four Tn5-transposon LPS mutants of Sinorhizobium meliloti (Tb9, Tb29, Ts22 and Ts32) have been studied. Each of four mutants has been established to contain a single insertion of Tn5-transposon in its genome. All mutations are located on a chromosome. Nodulation competitiveness (NC) of mutants towards the parent strain of S. meliloti CXM1-188 was investigated by resistant method using coinoculation of mutant and parent strain in the ratio 1:1. It was shown that NC was only 19-31% and 8-10%, for two strains Tb29 and Ts22, respectively which had lost the capability to synthesize higher molecular weight form of lipopolysaccharide (LPS1). Nodulation competitiveness of two other strains (Tb9 and Ts32) which retained the capability to synthesize LPS1 although in modified form varied from 49 to 62% and did not differ from NC of strain CXM1-188. The investigation of nodule formation rate has shown that four LPS-mutants did not differ from the parent strain by the number of root nodules. However the appearance of nodules induced by the mutant Tb29 was registered 7 days later than the nodules formed by other LPS-mutants and CXM1-188 strain. Obtained data concerning a single Tn5-insertion in genome of each of four S. meliloti LPS-mutants testify to the fact that both the disturbance of lipopolysaccharide synthesis and change of nodulation competitiveness in mutants Tb29 and Ts22 are results of a single mutation.