Department of Bacteriology, National Veterinary Institute (SVA), Uppsala, Sweden.
BMC Genomics. 2011 Apr 12;12:185. doi: 10.1186/1471-2164-12-185.
Clostridium botulinum strains can be divided into four physiological groups that are sufficiently diverged to be considered as separate species. Here we present the first complete genome of a C. botulinum strain from physiological group III, causing animal botulism. We also compare the sequence to three new draft genomes from the same physiological group.
The 2.77 Mb chromosome was highly conserved between the isolates and also closely related to that of C. novyi. However, the sequence was very different from the human C. botulinum group genomes. Replication-directed translocations were rare and conservation of synteny was high. The largest difference between C. botulinum group III isolates occurred within their surprisingly large plasmidomes and in the pattern of mobile elements insertions. Five plasmids, constituting 13.5% of the total genetic material, were present in the completed genome. Interestingly, the set of plasmids differed compared to other isolates. The largest plasmid, the botulinum-neurotoxin carrying prophage, was conserved at a level similar to that of the chromosome while the medium-sized plasmids seemed to be undergoing faster genetic drift. These plasmids also contained more mobile elements than other replicons. Several toxins and resistance genes were identified, many of which were located on the plasmids.
The completion of the genome of C. botulinum group III has revealed it to be a genome with dual identity. It belongs to the pathogenic species C. botulinum, but as a genotypic species it should also include C. novyi and C. haemolyticum. The genotypic species share a conserved chromosomal core that can be transformed into various pathogenic variants by modulation of the highly plastic plasmidome.
肉毒梭菌菌株可分为四个生理组，它们之间的差异足以被视为不同的种。本文呈现了首个来自生理组 III 的导致动物肉毒中毒的肉毒梭菌菌株的全基因组。我们还将该序列与来自同一生理组的三个新的草图基因组进行了比较。
2.77 Mb 的染色体在分离株之间高度保守，与新型肉毒梭菌也密切相关。然而，其序列与人类肉毒梭菌组的基因组有很大的不同。复制定向易位很少，且基因的排列高度保守。肉毒梭菌组 III 分离株之间最大的差异出现在它们非常大的质粒组和移动元件插入模式中。5 个质粒，占总遗传物质的 13.5%，存在于完整基因组中。有趣的是，与其他分离株相比，这组质粒有所不同。携带肉毒神经毒素的大质粒与染色体的保守水平相似，而中等大小的质粒似乎经历了更快的遗传漂移。这些质粒还包含比其他复制子更多的移动元件。鉴定出了几种毒素和抗性基因，其中许多位于质粒上。
完成肉毒梭菌组 III 的基因组揭示了它具有双重身份。它属于病原种肉毒梭菌，但作为基因型种，它也应该包括新型肉毒梭菌和溶血梭菌。基因型种共享一个保守的染色体核心，通过调节高度可塑的质粒组，可以将其转化为各种致病变体。
