16SrDNA同源性所揭示的双歧杆菌与有关细菌的亲缘关系

Phylogenetic relationship between the genus Bifidobacterium and related bacteria based on 16S rDNA homology

本研究测定了低GC含量的双歧杆菌 (Bifidobacteriuminopinatum )和新种B .thermaci dophilum的 16SrDNA全序列 ,在同另外 19个双歧杆菌及 8个相关细菌的 16SrDNA同源性分析的基础上构建了系统发育树。结果表明 :除低GC含量的B .inopinatum外 ,所有双歧杆菌的种在 16SrDNA序列相似性≥ 92 %的水平上聚类为一个簇群。尽管B .inopinatum与其它种的双歧杆菌的相似性只有87%～ 89% ,但它仍与双歧杆菌的关系最密切 ,而并未显示出与GC含量相近属的特殊亲缘关系。本研究结果未显示出在革兰氏阳性细菌分支中 ,由低GC到高GC含量的细菌种群的系统演化模式。此外 ,研究结果提示在细菌系统发育研究中 ,由 16SrDNA序列和基因组DNA同源性产生的矛盾需借助于其它保守的生物大分子来澄清。

In the present study, the 16S rDNA of Bifidobacterium inopinatum with low GC content and B.thermacidophilum sp. nov. was sequenced. A phylogenetic dendrogram was constructed using the two sequences and other 16S rDNA sequences of 19 Bifidobacterium spp. and eight related genera obtained from DNA databases. The results showed that except for B.inopinutum, all the bifidobacteria were clustered at similarity levels(≥92%) of 16S rDNA sequences. Although B.inopinutum showed a relatively lower similarity (87%～89%) with the other bifidobacteria, it was closely related to the Bifidobacterium spp. rather than to other gram_positive bacteria with similar GC content. This study did not reveal the evolutionary pattern from low GC to high GC content in the gram_positive bacterial phylum. In addition, the divergence between 16S rDNA sequence and genomic DNA GC content in the study of bacterial phylogenetics has to be resolved using other conserved macrobiological moleculars.