FUNCTIONS OF PLASMIDS IN RHIZOBIUM HUAKUII
紫云英根瘤菌质粒功能研究

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.