Massive horizontal gene transfer, strictly vertical inheritance and ancient duplications differentially shape the evolution of Bacillus cereus enterotoxin operons hbl, cytK and nhe.
Massive horizontal gene transfer, strictly vertical inheritance and ancient duplications differentially shape the evolution of Bacillus cereus enterotoxin operons hbl, cytK and nhe.
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DOI：
10.1186/s12862-015-0529-4
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发表时间：
2015-11-10
影响因子：
3.4
通讯作者：
Scherer S
中科院分区：
文献类型：
--
作者：
Böhm ME;Huptas C;Krey VM;Scherer S
广义蜡样芽孢杆菌包括八个密切相关的物种，包括人类病原体炭疽芽孢杆菌和蜡样芽孢杆菌。在B范围内。广义蜡状芽孢杆菌存在染色体和质粒编码的毒素。虽然呕吐毒素、炭疽和杀虫毒素的质粒介导的水平基因转移是已知的，但该组内肠毒素基因的进化尚未研究。我们报告了25个菌株的基因组装配草图，基于来自基因组序列的ANI的142个菌株的系统发育网络和基于全基因组SNP分析的系统发育。数据清楚地支持B的细分。cereus sensu lato分为七个系统发育组。而基团I、V和VII代表B。假蕈样菌B. pseudomycoides，B. toyonensis和B.细胞毒的菌株在种水平上是可区分的（ANI边界≥ 96%），归属于其他5个种的菌株不匹配致突变群。染色体肠毒素操纵子nheABC和hblCDAB在B内是丰富的。蜡状芽孢杆菌既从感染中分离出来，也从环境中分离出来。虽然在所有研究的菌株中有22%存在重复的hbl变体hbla，但nheABC的重复非常罕见（0.02%），并且似乎在遗传学上不稳定。毒素基因的分布与基于七个串联管家基因的主树相匹配，该主树描述了B中的种间关系。蜡状病毒的精确度不亚于全基因组比较。与肠毒素基因同源性的比较揭示了hbl、cytK和plcR水平转移的充分证据，以及两种毒素的频繁缺失和hbl的重复。没有发现nhe缺失的证据，nhe稳定的水平转移也很少见。因此，B.蜡状肠毒素操纵子的形状出乎意料地不同，原因尚不清楚。B中致病因子hbl、cytK和plcR的频繁交换。蜡状细胞似乎是B的一个重要机制。蜡样芽胞杆菌毒力演变，包括所谓的益生菌或非致病性菌种，这可能对风险评估程序产生影响。相比之下，完全垂直遗传的nhe观察，因为nhe阴性菌株似乎是非常罕见的，我们认为，健身损失可能与删除或水平转移的nhe操纵子。本文的在线版本（doi：10.1186/s12862-015-0529-4）包含补充材料，可供授权用户使用。
Bacillus cereus sensu lato comprises eight closely related species including the human pathogens Bacillus anthracis and Bacillus cereus. Within B. cereus sensu lato, chromosomally and plasmid-encoded toxins exist. While plasmid-mediated horizontal gene transfer of the emetic toxin, anthrax and insecticidal toxins is known, evolution of enterotoxin genes within the group has not been studied. We report draft genome assemblies of 25 strains, a phylogenetic network of 142 strains based on ANI derived from genome sequences and a phylogeny based on whole-genome SNP analysis. The data clearly support subdivision of B. cereus sensu lato into seven phylogenetic groups. While group I, V and VII represent B. pseudomycoides, B. toyonensis and B. cytotoxicus, which are distinguishable at species level (ANI border ≥ 96 %), strains ascribed to the other five species do not match phylogenic groups. The chromosomal enterotoxin operons nheABC and hblCDAB are abundant within B. cereus both isolated from infections and from the environment. While the duplicated hbl variant hbla is present in 22 % of all strains investigated, duplication of nheABC is extremely rare (0.02 %) and appears to be phylogenetically unstable. Distribution of toxin genes was matched to a master tree based on seven concatenated housekeeping genes, which depicts species relationships in B. cereus sensu lato as accurately as whole-genome comparisons. Comparison to the phylogeny of enterotoxin genes uncovered ample evidence for horizontal transfer of hbl, cytK and plcR, as well as frequent deletion of both toxins and duplication of hbl. No evidence for nhe deletion was found and stable horizontal transfer of nhe is rare. Therefore, evolution of B. cereus enterotoxin operons is shaped unexpectedly different for yet unknown reasons. Frequent exchange of the pathogenicity factors hbl, cytK and plcR in B. cereus sensu lato appears to be an important mechanism of B. cereus virulence evolution, including so-called probiotic or non-pathogenic species, which might have consequences for risk assessment procedures. In contrast, exclusively vertical inheritance of nhe was observed, and since nhe-negative strains appear to be extremely rare, we suggest that fitness loss may be associated with deletion or horizontal transfer of the nhe operon. The online version of this article (doi:10.1186/s12862-015-0529-4) contains supplementary material, which is available to authorized users.