Department of Bacteriology, National Veterinary Institute (SVA), SE 751 89 Uppsala, Sweden.
BMC Genomics. 2011 Aug 4;12:395. doi: 10.1186/1471-2164-12-395.
Brachyspira spp. colonize the intestines of some mammalian and avian species and show different degrees of enteropathogenicity. Brachyspira intermedia can cause production losses in chickens and strain PWS/AT now becomes the fourth genome to be completed in the genus Brachyspira.
15 classes of unique and shared genes were analyzed in B. intermedia, B. murdochii, B. hyodysenteriae and B. pilosicoli. The largest number of unique genes was found in B. intermedia and B. murdochii. This indicates the presence of larger pan-genomes. In general, hypothetical protein annotations are overrepresented among the unique genes. A 3.2 kb plasmid was found in B. intermedia strain PWS/AT. The plasmid was also present in the B. murdochii strain but not in nine other Brachyspira isolates. Within the Brachyspira genomes, genes had been translocated and also frequently switched between leading and lagging strands, a process that can be followed by different AT-skews in the third positions of synonymous codons. We also found evidence that bacteriophages were being remodeled and genes incorporated into them.
The accessory gene pool shapes species-specific traits. It is also influenced by reductive genome evolution and horizontal gene transfer. Gene-transfer events can cross both species and genus boundaries and bacteriophages appear to play an important role in this process. A mechanism for horizontal gene transfer appears to be gene translocations leading to remodeling of bacteriophages in combination with broad tropism.
短螺旋体属的物种定殖于一些哺乳动物和禽类的肠道中，表现出不同程度的肠致病性。中弯短螺旋体可导致鸡群生产损失，而 PWS/AT 菌株现在成为短螺旋体属中第四个完成基因组测序的菌株。
分析了中弯短螺旋体、B. murdochii、B. hyodysenteriae 和 B. pilosicoli 中的 15 类独特和共有基因。独特基因数量最多的是中弯短螺旋体和 B. murdochii。这表明存在更大的泛基因组。一般来说，独特基因中假设蛋白注释的数量较多。在中弯短螺旋体 PWS/AT 菌株中发现了一个 3.2kb 的质粒。该质粒也存在于 B. murdochii 菌株中，但不存在于其他 9 个短螺旋体分离株中。在短螺旋体基因组中，基因发生了易位，并且经常在领头链和滞后链之间切换，这一过程可以通过第三位置同义密码子的不同 AT 偏斜来跟踪。我们还发现了证据表明噬菌体正在被改造，基因被整合到它们中。
附加基因库塑造了物种特异性特征。它还受到还原基因组进化和水平基因转移的影响。基因转移事件可以跨越物种和属的界限，噬菌体似乎在这个过程中起着重要的作用。一种水平基因转移的机制似乎是导致噬菌体结构重塑的基因易位，同时具有广泛的嗜性。
