紫云英根瘤菌质粒功能研究

紫云英根瘤菌CH203含有3条质粒(pRHa,97MI);pRHb,168MD;pRHc,251MD为共生质粒),用带蔗糖敏感基因Tn5-sacB进行菌株质粒消除和质粒缺失突变株筛选,获得一系列突变株。与野生型菌相比,质粒pRHa的丢失导致菌株结无效根瘤,质粒pRHb的丢失使菌株失去共生能力,在TY培养基平板上菌落变得粗糙,失去了脂多糖(LPSI)。质粒pRHc(共生质粒)的丢失显然失去其菌株的共生能力,同时使菌株抗酸性明显减弱。质粒回复能恢复突变株的表现特征和共生能力。此外,紫云英根瘤菌CH205含有5条大小不同的质粒(分子量42MD～230MD),该菌株某些质粒的消除能显著增强菌株的结瘤固氮能力。研究结果也表明除共生质粒外,紫云英根瘤菌其它质粒明显影响菌株的共生效应。

FUNCTIONS OF PLASMIDS IN RHIZOBIUM HUAKUII

Rhizobium huakuii CH203 harbors three plasmids (pRHa, 97MD; pRHb, 108MD; pRHc, 251MD), and pRHc has been shown to be the symbiotic plasmid. By positive selection for curing and deletion of Rhizobium plasmid using transposon carrying Bacillus subtilus sucB gene, the derivatives cured of different plasmids were isolated. In comparison with the parent strain CH203, the strain crued of pRHa lost its ability to fix nitrogen, only forming ineffective nodules. The derivative crued of pRHb showed no nodulating on root of host plant. The strain lacking pRHb had rough colonies on TY medium and lost lipopolysaccharide (LPS I). The strain lacking pRHc(sym plasmid) obviously lost its symbiotic performance. Furthermore, curing of each plasmid in strain CH203 reduced the strain's tolerance to acid. Complementation of each plasmid cured with corresponding plasmid restored their original phenotypes. The study suggests that other plasmids in addition to sym plasmid affect symbiotic performance. Further studying on function of plasmids in Rhizobium huakuii CH205 also approved the hypothesis.