Stinear T P, Jenkin G A, Johnson P D, Davies J K
Bacterial Pathogenesis Research Group, Department of Microbiology, Monash University, Clayton, Victoria, Australia.
J Bacteriol. 2000 Nov;182(22):6322-30. doi: 10.1128/JB.182.22.6322-6330.2000.
Previous studies of the 16S rRNA genes from Mycobacterium ulcerans and Mycobacterium marinum have suggested a very close genetic relationship between these species (99.6% identity). However, these organisms are phenotypically distinct and cause diseases with very different pathologies. To investigate this apparent paradox, we compared 3,306 nucleotides from the partial sequences of eight housekeeping and structural genes derived from 18 M. ulcerans strains and 22 M. marinum strains. This analysis confirmed the close genetic relationship inferred from the 16S rRNA data, with nucleotide sequence identity ranging from 98.1 to 99.7%. The multilocus sequence analysis also confirmed previous genotype studies of M. ulcerans that have identified distinct genotypes within a geographical region. Single isolates of both M. ulcerans and M. marinum that were shown by the sequence analysis to be the most closely related were then selected for further study. One- and two-dimensional pulsed-field gel electrophoresis was employed to compare the architecture and size of the genome from each species. Genome sizes of approximately 4.4 and 4.6 Mb were obtained for M. ulcerans and M. marinum, respectively. Significant macrorestriction fragment polymorphism was observed between the species. However, hybridization analysis of DNA cleaved with more frequently cutting enzymes identified significant preservation of the flanking sequence at seven of the eight loci sequenced. The exception was the 16S rRNA locus. Two high-copy-number insertion sequences, IS2404 and IS2606, have recently been reported in M. ulcerans, and significantly, these elements are not present in M. marinum. Hybridization of the AseI restriction fragments from M. ulcerans with IS2404 and IS2606 indicated widespread genome distribution for both of these repeated sequences. Taken together, these data strongly suggest that M. ulcerans has recently diverged from M. marinum by the acquisition and concomitant loss of DNA in a manner analogous to the emergence of M. tuberculosis, where species diversity is being driven mainly by the activity of mobile DNA elements.
先前对溃疡分枝杆菌和海分枝杆菌16S rRNA基因的研究表明，这些菌种之间存在非常密切的遗传关系（序列同一性为99.6%）。然而，这些微生物在表型上是不同的，并且会引发具有截然不同病理特征的疾病。为了探究这一明显的矛盾现象，我们比较了来自18株溃疡分枝杆菌菌株和22株海分枝杆菌菌株的8个管家基因和结构基因部分序列中的3306个核苷酸。该分析证实了从16S rRNA数据推断出的密切遗传关系，核苷酸序列同一性范围为98.1%至99.7%。多位点序列分析也证实了先前对溃疡分枝杆菌的基因型研究，这些研究已在一个地理区域内鉴定出不同的基因型。然后选择序列分析显示为关系最密切的溃疡分枝杆菌和海分枝杆菌的单株分离菌进行进一步研究。采用一维和二维脉冲场凝胶电泳来比较每个菌种基因组的结构和大小。溃疡分枝杆菌和海分枝杆菌的基因组大小分别约为4.4 Mb和4.6 Mb。在这两个菌种之间观察到显著的宏观限制性片段多态性。然而，用切割频率更高的酶切割DNA后的杂交分析表明，在测序的8个位点中的7个位点，侧翼序列有显著的保留。例外的是16S rRNA位点。最近在溃疡分枝杆菌中报道了两个高拷贝数插入序列，即IS2404和IS2606，重要的是，这些元件在海分枝杆菌中不存在。溃疡分枝杆菌的AseI限制性片段与IS2404和IS2606的杂交表明这两个重复序列在基因组中广泛分布。综上所述，这些数据有力地表明，溃疡分枝杆菌最近是通过获取并伴随DNA丢失而从海分枝杆菌分化出来的，其方式类似于结核分枝杆菌的出现，在结核分枝杆菌中，物种多样性主要由可移动DNA元件的活性驱动。
