摘要

炭疽杆菌是一种革兰氏阳性的内生孢子形成细菌，在人类和动物中都会产生炭疽。在赞比亚，炭疽病病例经常在牲畜和野生动物中报告，偶尔传染给人类，在该国造成严重的公共卫生问题。为了解赞比亚炭疽杆菌菌株的遗传多样性，我们对全国分离的炭疽芽孢杆菌菌株的基因组DNA进行了测序和比较。单核苷酸多态性将这些菌株聚类成三组。基因组序列比较揭示了属于其中一组的菌株的大量缺失，可能是由于一对rRNA操纵子之间的不等交换。缺失的基因组区域包括赋予杆菌肽抗性的基因，并且具有缺失的菌株被证实具有杆菌肽抗性的丧失。在一些远离赞比亚菌株的系统发育上的炭疽芽孢杆菌菌株中也观察到rRNA操纵子之间的类似缺失。侧翼为rRNA操纵子的杆菌肽抗性基因的结构仅在蜡状芽孢杆菌组的成员中保守。本研究中确定的炭疽芽孢杆菌菌株的多样性和基因组特征将有助于赞比亚的炭疽遗传标记的开发和治疗。重要性炭疽病是由炭疽杆菌（Bacillus anthracis）引起的，炭疽芽孢杆菌是一种形成内生孢子的土壤细菌。已知炭疽芽孢杆菌的遗传多样性与芽孢杆菌属的遗传多样性相比较低。在这项研究中，我们对赞比亚炭疽芽孢杆菌分离株进行了全基因组测序，以了解密切相关菌株之间的遗传多样性。基因组序列的比较揭示，基于分布在整个基因组中的单核苷酸多态性，将密切相关的菌株分成三组。在含有侧翼为rRNA操纵子的杆菌肽抗性基因簇的区域中检测到大的基因组缺失，导致杆菌肽抗性的丧失。缺失区域的结构在蜡状芽孢杆菌种群中也是保守的，具有删除和扩增的潜力，因此可能使物种能够灵活地控制杆菌肽抗性以适应进化。

Bacillus anthracis is a Gram-positive endospore-forming bacterial species that causes anthrax in both humans and animals. In Zambia, anthrax cases are frequently reported in both livestock and wildlife, with occasional transmission to humans, causing serious public health problems in the country. To understand the genetic diversity of B. anthracis strains in Zambia, we sequenced and compared the genomic DNA of B. anthracis strains isolated across the country. Single nucleotide polymorphisms clustered these strains into three groups. Genome sequence comparisons revealed a large deletion in strains belonging to one of the groups, possibly due to unequal crossing over between a pair of rRNA operons. The deleted genomic region included genes conferring resistance to bacitracin, and the strains with the deletion were confirmed with loss of bacitracin resistance. Similar deletions between rRNA operons were also observed in a few B. anthracis strains phylogenetically distant from Zambian strains. The structure of bacitracin resistance genes flanked by rRNA operons was conserved only in members of the Bacillus cereus group. The diversity and genomic characteristics of B. anthracis strains determined in this study would help in the development of genetic markers and treatment of anthrax in Zambia. IMPORTANCE Anthrax is caused by Bacillus anthracis, an endospore-forming soil bacterium. The genetic diversity of B. anthracis is known to be low compared with that of Bacillus species. In this study, we performed whole-genome sequencing of Zambian isolates of B. anthracis to understand the genetic diversity between closely related strains. Comparison of genomic sequences revealed that closely related strains were separated into three groups based on single nucleotide polymorphisms distributed throughout the genome. A large genomic deletion was detected in the region containing a bacitracin resistance gene cluster flanked by rRNA operons, resulting in the loss of bacitracin resistance. The structure of the deleted region, which was also conserved among species of the Bacillus cereus group, has the potential for both deletion and amplification and thus might be enabling the species to flexibly control the level of bacitracin resistance for adaptive evolution.

https://www.ncbi.nlm.nih.gov/pubmed/30417107