Cardazzo Barbara, Negrisolo Enrico, Carraro Lisa, Alberghini Leonardo, Patarnello Tomaso, Giaccone Valerio
Department of Public Health, Comparative Pathology and Veterinary Hygiene, University of Padova, Agripolis, Viale dell'Università 16, 35020 Legnaro, Italy.
Appl Environ Microbiol. 2008 Feb;74(3):850-60. doi: 10.1128/AEM.01495-07. Epub 2007 Dec 14.
In the present study we characterized 47 food-borne isolates of Bacillus cereus using multilocus sequence typing (MLST). Newly determined sequences were combined with sequences available in public data banks in order to produce the largest data set possible. Phylogenetic analysis was performed on a total of 296 strains for which MLST sequence information is available, and three main lineages--I, II, and III--within the B. cereus complex were identified. With few exceptions, all food-borne isolates were in group I. The occurrence of horizontal gene transfer (HGT) among various strains was analyzed by several statistical methods, providing evidence of widespread lateral gene transfer within B. cereus. We also investigated the occurrence of toxin-encoding genes, focusing on their evolutionary history within B. cereus. Several patterns were identified, indicating a pivotal role of HGT in the evolution of toxin-encoding genes. Our results indicate that HGT is an important element in shaping the population structure of the B. cereus complex. The results presented here also provide strong evidence of reticulate evolution within the B. cereus complex.
在本研究中，我们使用多位点序列分型（MLST）对47株食源性蜡样芽孢杆菌分离株进行了特征分析。将新测定的序列与公共数据库中可用的序列相结合，以生成尽可能大的数据集。对总共296株有MLST序列信息的菌株进行了系统发育分析，在蜡样芽孢杆菌复合体中鉴定出三个主要谱系——I、II和III。除少数例外，所有食源性分离株都属于I组。通过几种统计方法分析了不同菌株间水平基因转移（HGT）的发生情况，为蜡样芽孢杆菌内广泛的侧向基因转移提供了证据。我们还研究了毒素编码基因的发生情况，重点关注它们在蜡样芽孢杆菌内的进化历史。识别出了几种模式，表明HGT在毒素编码基因的进化中起关键作用。我们的结果表明，HGT是塑造蜡样芽孢杆菌复合体种群结构的一个重要因素。这里呈现的结果也为蜡样芽孢杆菌复合体内的网状进化提供了有力证据。
