Background Thermophilic bacilli in both aerobic or facultative anaerobic forms have been isolated for over a hundred years from different mesophilic or thermophilic environments as they are potential source of bioactive secondary metabolites. But the taxonomic resolution in the Bacillus genus at species or at strain level is very challenging for the insufficient divergence of the 16S rRNA genes. One such recurring problem is among Bacillus anthracis, B. cereus and B. thuringiensis. The disease-causing B. anthracis strains have their characteristic virulence factors coded in two well-known plasmids, namely pXO1 (toxin genes) and pXO2 (capsule genes). Objective The present study aimed at the molecular and genomic characterization of a recently reported thermophilic and environmental isolate of B. anthracis, strain PFAB2. Methods We performed comparative genomics between the PFAB2 genome and different strains of B. anthracis, along with closely related B. cereus strains. Results The pangenomic analysis suggests that the PFAB2 genome harbors no complete prophage genes. Cluster analysis of Bray-Kurtis similarity resemblance matrix revealed that gene content of PFAB2 is more closely related to other environmental strains of B. anthracis. The secretome analysis and the in vitro and in vivo pathogenesis experiments corroborate the avirulent phenotype of this strain. The most probable explanation for this phenotype is the apparent absence of plasmids harboring genes for capsule biosynthesis and toxins secretion in the draft genome. Additional features of PFAB2 are good spore-forming and germinating capabilities and rapid replication ability. Conclusion The high replication rate in a wide range of temperatures and culture media, the non-pathogenicity, the good spore forming capability and its genomic similarity to the Ames strain together make PFAB2 an interesting model strain for the study of the pathogenic evolution of B. anthracis.

中文翻译：

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PFAB2 的分子和基因组特征：从印度温泉中分离出的无毒力炭疽芽孢杆菌菌株

背景 好氧或兼性厌氧形式的嗜热杆菌已经从不同的中温或嗜热环境中分离了一百多年，因为它们是生物活性次级代谢物的潜在来源。但是，由于 16S rRNA 基因的分歧不足，芽孢杆菌属在物种或菌株水平上的分类学分辨率非常具有挑战性。一个这样的反复出现的问题是炭疽杆菌、蜡状芽孢杆菌和苏云金芽孢杆菌。引起疾病的炭疽芽孢杆菌菌株具有在两个众所周知的质粒中编码的特征毒力因子，即 pXO1（毒素基因）和 pXO2（胶囊基因）。目的 本研究旨在对最近报道的一种嗜热和环境分离的炭疽杆菌 PFAB2 菌株进行分子和基因组表征。方法 我们在 PFAB2 基因组和不同的炭疽芽孢杆菌菌株以及密切相关的蜡状芽孢杆菌菌株之间进行了比较基因组学。结果泛基因组分析表明PFAB2基因组不包含完整的前噬菌体基因。Bray-Kurtis 相似性相似矩阵的聚类分析表明，PFAB2 的基因含量与炭疽杆菌的其他环境菌株关系更密切。分泌组分析和体外和体内发病机制实验证实了该菌株的无毒表型。对这种表型最可能的解释是在基因组草图中明显不存在含有胶囊生物合成和毒素分泌基因的质粒。PFAB2 的其他特点是良好的孢子形成和发芽能力以及快速复制能力。