Genetic analysis of Bradyrhizobium japonicum isolates possessing highly reiteratied DNA sequences

利用重复序列法（RSalpha和rbeta）对日本本土慢生根瘤菌进行DNA指纹图谱分析，发现来自日本2个产地的多株慢生根瘤菌具有高度重复的RSs （HRS分离株）。一些HRS分离株在其基因组上含有大约200个RSalpha拷贝。脉冲场凝胶电泳分析表明，RSalpha拷贝分布在HRS分离物基因组的74%区域，正常分离物基因组的17%区域。在共生特征方面，HRS分离株结瘤、氮酶活性和氢化酶活性与正常菌株相似。然而，HRS和正常分离株在YM培养基中的生长速率不同。HRS分离株的世代时间为5 ~ 9 h，而正常分离株的世代时间为4 ~ 6 h。这些结果强烈提示日本血吸虫HRS分离株的基因组发生了RSs转位和基因组重排。

During DNA fingerprinting of indigenous Bradyrhizobium japonicum by repeated sequence (RSalpha and RSbeta), we found many isolates possessing highly reiterated RSs (HRS isolates) from two fields in Japan. Some HRS isolates harbors approximately 200 copies of RSalpha on their genomes. Analysis of pulse field gel electrophoresis indicates that RSalpha copies are distributed to 74% region on HRS isolate genomes and to 17% region on normal isolate genomes. With respect to symbiotic features of HRS isolates, nodulation, nitrogenase activity and hydrogenase activity of HRS isolates were similar to that of normal isolates. However, HRS and normal isolates differed in growth rates in YM medium. Generation time of HRS isolates showed 5-9 h, While normal isolates showed 4-6 h of genaration time. These results strongly suggest that RSs transposition and genomic rearrangement occur on the genomes of B.japonicum HRS isolates.