Jumas-Bilak E, Michaux-Charachon S, Bourg G, O'Callaghan D, Ramuz M
Institut National de la Santé et de la Recherche Médicale, Unité 431, Faculté de Médecine, Nîmes, France.
Mol Microbiol. 1998 Jan;27(1):99-106. doi: 10.1046/j.1365-2958.1998.00661.x.
We have studied the genomic structure and constructed the SpeI, PacI and I-CeuI restriction maps of the four biovars of the pathogenic bacterium Brucella suis. B. suis biovar 1 has two chromosomes of 2.1 Mb and 1.15 Mb, similar to those of the other Brucella species: B. melitensis, B. abortus, B. ovis and B. neotomae. Two chromosomes were also observed in the genome of B. suis biovars 2 and 4, but with sizes of 1.85 Mb and 1.35 Mb, whereas only one chromosome with a size of 3.1 Mb was found in B. suis biovar 3. We show that the differences in chromosome size and number can be explained by rearrangements at chromosomal regions containing the three rrn genes. The location and orientation of these genes confirmed that these rearrangements are due to homologous recombination at the rrn loci. This observation allows us to propose a scheme for the evolution of the genus Brucella in which the two chromosome-containing strains can emerge from an hypothetical ancestor with a single chromosome, which is probably similar to that of B. suis biovar 3. As the genus Brucella is certainly monospecific, this is the first time that differences in chromosome number have been observed in strains of the same bacterial species.
我们研究了致病性猪布鲁氏菌四个生物变种的基因组结构，并构建了SpeI、PacI和I-CeuI限制酶切图谱。猪布鲁氏菌生物变种1有两条染色体，大小分别为2.1 Mb和1.15 Mb，与其他布鲁氏菌物种（羊布鲁氏菌、牛布鲁氏菌、绵羊布鲁氏菌和墨西哥布鲁氏菌）的染色体相似。在猪布鲁氏菌生物变种2和4的基因组中也观察到两条染色体，但大小分别为1.85 Mb和1.35 Mb，而在猪布鲁氏菌生物变种3中仅发现一条大小为3.1 Mb的染色体。我们表明，染色体大小和数量的差异可以通过包含三个rrn基因的染色体区域的重排来解释。这些基因的位置和方向证实，这些重排是由于rrn位点的同源重组所致。这一观察结果使我们能够提出一个布鲁氏菌属的进化方案，其中含有两条染色体的菌株可能从一个假设的具有单条染色体的祖先演化而来，这个祖先可能与猪布鲁氏菌生物变种3的染色体相似。由于布鲁氏菌属肯定是单种属，这是首次在同一细菌物种的菌株中观察到染色体数量的差异。
