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Genetic analysis of a cluster of exo genes required for EPS synthesis in Rhizobium astragalus

Huang Jianbing, Wang Jianhai, Hua Zhen, Shu WenYin, Song Hongyu

Shanghai Institute of Plant Physiology,The Chinese Academmy of Sciences.Shanghai 200032

Abstract

Twelve exopolysaccharide(EPS)-deficient(Exo) mutants were isolated after Rhizobium astragalus strain 107 was subjected to transposon Tn5 mutagenesis.Using the broad host range vector plasmid pMN2,a kanamycin-sensitive derivative of plasmid R68.45,seven R-primmes (exoR^)from seven EPS~(-) mutants of Rhizobium astragalus strain 107 were isolad.Each exoR^ plasmid carried a specific Tn5 insertion site and its flanking fragment coding for exopolysaccharide synthesis. When these exoR^ plasmids were introduced back into the twelve mutants,exoR^ plasmids were able to complement the EPS~(-) phenotype of most mutants. Based on complementation analysis, twelve EPS~(-) mutants were classified into six distinct complementation groups. Five of the six exoloci were genetically linked.By restriction enzyme analysis, it was shown that in all exoR^ plasmids but exoR-02 and exoR^-4,the foreign DNA fragments were integrated between the tandem repeat sequence IS21.The mobilization of megaplasmid and Southern hybridization experiments showed that the probeexctly hybridized the total DNA of these strains with the pRa 107b. It means that the five linked exo loci were located on the megaplas-mid pRa107b.

Key words: Genetic analysis;Rhizobium astragalus;Exocluster;Exoploysaccharide

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Citing This Article：

Huang Jianbing, Wang Jianhai, Hua Zhen, Shu WenYin, Song Hongyu. Genetic analysis of a cluster of exo genes required for EPS synthesis in Rhizobium astragalus. Acta Physiol Sin 1996; 48 (2): (in Chinese with English abstract).