根瘤菌基因组结构的多样性及其与系统发育的关系*

研究探讨依据基因组结构对根瘤菌进行系统发育分类的可行性。采用I-CeuI酶切及脉冲场电泳分析确定25株根瘤菌模式菌株的基因组结构，据此对根瘤菌进行聚群，并与16S rRNA聚群结果相比较。依据基因组结构的近似或不同，25株根瘤菌共分为11个基因组型(genome type，GT)。这些基因组型与依据16S rRNA序列的聚群结果大体一致，其不同之处显示了两种方法各自的特点。因此，基因组的物理结构，即本研究中rm纵子的数量及其在基因组上的位置，可作为系统发育关系的标志而用于根瘤菌的分类。

DIVERSITY OF GENOME STRUCTURE AMONG RHIZOBIA AND ITS CORRELATION WITH PHYLOGENY EVALUATED BY I-CeuI

This study has attempted to categorize the rhizobia based on their gen omic features, hoping to use them as phylogenetic markers for natural classifica tion of rhizobia Genome structures of 25 rhizobial type strains were resolved by I CeuI cleavage and subsequent pulsed field gel electrophoresis (PFGE) Then they were divided into groups according to the similarity and differences of th eir genome structures The 25 rhizobial strains were grouped into 11 genome ty p es (GTs) These rhizobial strains were also clustered by 16S rRNA sequence com p arison The two methods had a general agreement, with each also reflecting dif f erent aspect of the genomes It can be concluded that physical structure of th e bacterial genome, here specifically the copy number and genomic distribution of genes coding for ribosomal RNA, can unambiguously be revealed by the endonuclea se I CeuI and used as phylogenetic marker to categorize rhizobia according to evolutionary relationship