初步研究我国土拉菌的亚种及遗传进化关系

Preliminary study and phylogenetic analysis of the subspecies of Francisella tularensis in China

目的研究我国土拉弗朗西斯菌(土拉菌)亚种类型及各菌株之间的遗传进化关系。方法对于来源于我国北方地区的10株土拉菌,采用2种型特异引物C1C4和RD1进行PCR,根据扩增产物片段长度来判断所属亚种;同时,使用fopA、tul4和16SrRNA引物,进行3种特异基因的PCR,然后测序;这10株土拉菌及网上已公布基因组序列的3株B型土拉菌、1株subsp.novicida,应用MEGA4软件,进行3种特异基因为基础的系统进化分析。结果采用2种型特异引物C1C4和RD1,鉴定10株土拉菌均为B型亚种;根据MEGA4构建的进化树,我国10株土拉菌可以分为2种基因型,410108、410109和410111为B1型,另外7株土拉菌为B2型;而国外的3株B型土拉菌归为B3型。结论我国北方地区分离的土拉菌可能以B型为主,对于土拉菌B型亚种的起源,我国土拉菌可能早于欧美国家。3种基因为基础的系统进化分析可作为土拉菌基因分型的一种可靠方法。

Objective To study the subspecies of Francisella tularensis in China and the genetic relationships among the various strains of them. Methods Ten strains of F. tularensis from North China were subject to PCR using two specific primers C1C4 and RD1. Their subspecies were identified based on the length of the amplification products. At the same time, PCR on three specific genes was performed using fopA, tul4 and 16S rRNA primers, followed by sequencing. Based on the three specific genes, phylogenetic analysis was conducted using MEGA 4 software to involve the 10 strains of F. tularensis and the three strains of F. tularensis type B and one strain of subsp. novicida published on the NCBI website. Results The 10 strains of F. tularensis were identified as type B based on the PCR results using two specific primers C1C4 and RD1. According to the phylogenetic tree structured by MEGA 4, the 10 strains of F. tularensis from China can be classified into two types： B1 type, including 410108, 410109 and 410111, and B2 type including the other seven strains. In contrast, the three foreign strains were of type B3. Conclusion The F. tularensis isolated in North China may be predominated by type B. As for the origin of F. tularensis type B, the F. tularensis in China has probably emerged earlier than those in Europe and America. Phylogenetic analysis based on the three specific genes can be used as a reliable genotyping tool for F. tularensis.