PDF(Pubmed)
Abstract：
Bacillus cereus biovar anthracis (Bcbva) is an untypical pathogen causing a fatal anthrax-like disease in a variety of wildlife species in African rainforest areas. In contrast to Bacillus anthracis and most species of the B. cereus group, all strains of the Bcbva cluster contain a 22 kb insertion in the sigK gene which encodes the essential late sporulation sigma factor σK. This insertion is excised during sporulation in a site-specific recombination process resulting in an intact sigK gene and a circular molecule. The sporulation kinetics of two strains each of Bcbva and B. anthracis were compared by the expression analysis of eight sporulation-associated genes, including sigK, using reverse transcriptase quantitative real-time PCR. In addition, morphological sporulation stages were analyzed and quantified by electron microscopy. Our results indicated that the necessary excision of the insertion in Bcbva neither delayed nor inhibited its sporulation. In two spontaneous mutants of Bcbva, the excision of the sigK insertion and sporulation were impeded due to mutations in the spo0A and spoVG regulator genes, respectively. The spo0A frameshift mutation was overcome by intragenic suppression in a revertant which was able to sporulate normally, despite an M171S amino acid exchange in the global regulator Spo0A. A screening of the NCBI database identified further strains of the B. cereus group which possess unrelated insertions in the sigK gene, and two strains containing almost identical insertions at the same gene position. Some of the sigK insertions encode putative prophages, whereas the Bcbva insertion encoded a type I restriction-modification system. The function of these insertions and if they are possibly essential for sporulation remains to be assessed.
摘要：
蜡状芽孢杆菌炭疽杆菌（Bcbva）是一种非典型的病原体，可在非洲雨林地区的各种野生动植物中引起致命的炭疽样疾病。与炭疽芽孢杆菌和蜡状芽孢杆菌组的大多数物种相反，Bcbva簇的所有菌株在sigK基因中都包含22kb的插入，该基因编码必需的晚期孢子形成sigma因子σK。该插入在孢子形成过程中以位点特异性重组过程切除,产生完整的sigK基因和环状分子。通过8个孢子形成相关基因的表达分析，比较了Bcbva和炭疽芽孢杆菌两个菌株的孢子形成动力学，包括SigK,使用逆转录酶定量实时PCR。此外,通过电子显微镜对形态孢子形成阶段进行分析和定量。我们的结果表明，在Bcbva中插入的必要切除既不会延迟也不会抑制其孢子形成。在Bcbva的两个自发突变体中，由于spo0A和spoVG调节基因的突变，sigK插入和孢子形成的切除受到阻碍，分别。spo0A移码突变通过能够正常形成孢子的回复体中的基因内抑制来克服，尽管在全球监管机构Spo0A中进行了M171S氨基酸交换。对NCBI数据库的筛选确定了蜡状芽孢杆菌组的其他菌株，这些菌株在sigK基因中具有无关的插入，和两个菌株在相同的基因位置包含几乎相同的插入。一些sigK插入编码推定的预言，而Bcbva插入编码了I型限制修改系统。这些插入的功能以及它们是否可能对孢子形成至关重要仍有待评估。
