Studying Of Gene TsT And SiR In Sinorhizobium Fredii WGF03

Sulfur is one of biological chemical element, necessary for interaction with nitrogen.it not only can be used as a biological macromolecular structure components, but also can play a certain role in metabolism. In recent years, research has shown that the modificaton to the reducted end of Nod factor, its sulfide modified determines the host specificity of the rhizobia.Thiosulfate sulfur transferase is encoded by the TsT gene.Using the Blast of the NCBI web, TsT gene shared95%identities at nucleotide level and98%positives at amino acid level with the reported TsT gene of Rhizobium sp. NGR234.To study the function of genes, deletion mutant TsTI was constructed respectively by homologous double exchange using pK18mobsacB.Deletion mutant of TsT gene, were unable to grow on MM medium with thiosulfate as sole sulfur source;while could grow on MM medium with sulfate,sulfite, cysteine or methionine as sole sulfur source.Compared with the wild strain S.fredii WGF03, the growth situations of deletion mutants TsTI showed no difference under the culture conditions with ammonium chloride as the sole nitrogen source, but the growth rate of mutants was decreased on MM medium with sodium nitrate as sole nitrogen source. Plant tests showed that the nodulation time of mutants was one day later of the wild strain S.fredii WGF03, its nodulate competitiveness and nodules number per plant were decreased too. There were significant differences in nodulation efficiency and the ability of nitrogen-fixation.Sulfite reductase is an enzyme in the sulfur metabolic pathway, can reduce sulfite to be sulfide.the enzyme is encoded by the SiR gene. Using the Blast of the NCBI web, SiR gene shared96%identities at nucleotide level and98%positives at amino acid level with the reported SiR gene of Rhizobium sp. NGR234.To study the function of genes, deletion mutant SiRI was constructed respectively by homologous double exchange using pK18mobsacB.deletion mutant of SiR gene, were unable to grow on MM medium with sulfate or sulflte as sole source; while could grow on MM medium with thiosulfate, cysteine or methionine as sole sulfur source.Compared with the wild strain S.fredii WGF03, the growth situations of deletion mutants SiRI showed no difference under the culture conditions with ammonium chloride as the sole nitrogen source, but the growth rate of mutants was decreased on MM medium with sodium nitrate as sole nitrogen source. Plant tests showed that the nodulation time of mutants was two day later of the wild strain S.fredii WGF03, its nodulate competitiveness and nodules number per plant were decreased too. There were significant differences in nodulation efficiency and the ability of nitrogen-fixation.