华癸中生根瘤菌(Mesorhizobium huakuii)研究进展

综述了华癸中生根瘤菌(Mesorhizobium huakuii)遗传多样性、质粒多样性、质粒的功能、结瘤因子、结瘤基因、胞外多糖等方面的研究进展。这类菌只能在紫云英上结瘤,1997年并入Mesorhizobium。选取大量菌株进行REP-PCR、16S和23S rDNAPCR-RFLP等分析,揭示其分为16种16S rDNA基因型。选用不同16S rDNA基因型的部分代表菌株进行部分16S rDNA测序。能够在紫云英上结瘤的根瘤菌可以分为2个类群。表明这类菌具有遗传多样性,存在不同的种。它们多数含共生质粒,共生质粒定位于最大或次大质粒上,质粒数1~5个不等,其分子量范围在53~906 kb之间。质粒缺失菌株表现为不结瘤(Nod-)和结瘤而不固氮(Nod ,Nif-)。某些质粒缺失还影响LPS合成、抗酸性、竞争结瘤能力。其结瘤因子能诱导紫云英根毛变形,它们的结瘤因子结构类似于苜蓿根瘤菌的结瘤因子。它们的结瘤基因具独特性,nodA与nodBC分隔一定距离,且具有保守性。它们产生的胞外多糖在侵染结瘤过程中发挥重要作用。

Researches on Mesorhizobium huakuii

The diversity of genetics and plasmids,functions of plasmids,Nod factors,nod genes and exopolysaccharide in Mesorhizobium huakuii were reviewed.Mesorhizobium huakuii could only form nodules in Astragalus sinicus L.,and was incorporated in Mesorhizobium in 1997.Lots of strains were isolated and characterized by PCR and RFLP analysis of 16S rDNA,23S rDNA.Results indicated that M.huakuii was belonged to two groups.The minor group could be a new species in Mesorhizobium.The strains generally harbored 1~5 plasmids and the symbiotic genes located on the largest or second one,pSym.Its sequence was between 53 kb and 906 kb.Some deleted plasmids showed Nod~(-)and Nod~(-)Fix~(-),other deleted plasmids affected synthesis of LPS,tolerance to acid,abilities of nodulation competition.Nod factors of M.huakuii could provoke root hair deformation in A.sinicus L..Its chemical structure was similar to Nod factors of Sinorhizobium melitoti.The nodA was separated from nodBC.This was unique nod gene organization and nodA gene sequences were highly conseved among different types of M.huakuii.The exopolysaccharides produced by M.huakuii could affect the infection and nodule formation.