Studies On The Diversity Of Plasmid Replication Gene RepC Of Sinorhizobium Fredii

1. Two to four indigenous plasmids were detected from thirty three strains of Sinorhizobium fredii by using Eckhardt fast detection method.2. A pair of primer RC1/RC3 was designed according to conservative sequences of repC gene and used for the amplification of repC genes from the 33 strains of S. fredii tested, 3 strains of Mesorhizobium huakuii and 1 strain of Bradyrhizobium japonicum. The results suggested that the repC gene existed in most strains of Sinorhizobium fredii. The results indicated that most Sinorhizobium fredii plasmids could be grouped into repABC family.3. Amplified repC gene fragments were cloned into pMD18-T and then sequenced. The sequences were used to compare with repC genes reported in the literature. Results from cluster analysis indicated that strains tested could be divided into group a and group b. The sequences in the same group were very conservative but had great differences from those in the other group. The repC gene of group b was significantly different from repC genes reported. Compared to results of cluster analysis based on 16S rDNA RFLP and gene sequencing, strains isolated from different plants or different environmental sampling sites might have the same repC sequence.There were also no correlations between repC gene and phenotypic characteristics.4. Southern hybridization was conducted between plasmids isolated from strains tested and repC probes of the typical strains from group IBa orllb. The sizes of hybridized band were different and only one positive band was detected for each strain which indicated that repC types were composed of different plasmid types. None of strains tested in one repABC family but belonged to different incompatibility groups.