Scarff Jennifer M, Raynor Malik J, Seldina Yuliya I, Ventura Christy L, Koehler Theresa M, O'Brien Alison D
Department of Microbiology and Immunology, Uniformed Services University of the Health Sciences, Bethesda, MD, USA.
Department of Microbiology and Molecular Genetics, The University of Texas Health Sciences Center at Houston, Houston, TX, USA.
Mol Microbiol. 2016 Nov;102(4):545-561. doi: 10.1111/mmi.13478. Epub 2016 Sep 4.
AtxA is a critical transcriptional regulator of plasmid-encoded virulence genes in Bacillus anthracis. Bacillus cereus G9241, which caused an anthrax-like infection, has two virulence plasmids, pBCXO1 and pBC210, that each harbor toxin genes and a capsule locus. G9241 also produces two orthologs of AtxA: AtxA1, encoded on pBCXO1, and AtxA2, encoded on pBC210. The amino acid sequence of AtxA1 is identical to that of AtxA from B. anthracis, while the sequences of AtxA1 and AtxA2 are 79% identical and 91% similar to one another. We found by qRT-PCR that AtxA1 and AtxA2 function as positive regulators of toxin (AtxA1) and capsule operon (both) transcription in G9241 and that a ΔatxA1 mutant produced lower levels of the anthrax toxins and no hyaluronic acid capsule. Deletion of atxA1 or atxA2 decreased the virulence of spores administered intranasally or subcutaneously to C57BL/6 mice but not to A/J mice, and deletion of both genes rendered spores avirulent in A/J mice. In addition, unlike AtxA1, AtxA2 did not form stable homomultimers in vitro, although AtxA1 and AtxA2 formed heterodimers. Our data show that AtxA1 is the primary regulator of G9241 virulence factor expression and that AtxA1 and AtxA2 are both required for full virulence.
AtxA是炭疽芽孢杆菌中质粒编码的毒力基因的关键转录调节因子。蜡样芽孢杆菌G9241引起了类似炭疽的感染，它有两个毒力质粒，pBCXO1和pBC210，每个质粒都含有毒素基因和一个荚膜基因座。G9241还产生了AtxA的两个直系同源物：AtxA1，由pBCXO1编码；AtxA2，由pBC210编码。AtxA1的氨基酸序列与炭疽芽孢杆菌的AtxA相同，而AtxA1和AtxA2的序列彼此相同性为79%，相似性为91%。我们通过qRT-PCR发现，AtxA1和AtxA2在G9241中作为毒素（AtxA1）和荚膜操纵子（两者）转录的正调节因子起作用，并且ΔatxA1突变体产生的炭疽毒素水平较低且没有透明质酸荚膜。缺失atxA1或atxA2会降低经鼻内或皮下接种到C57BL/6小鼠但不会降低接种到A/J小鼠的孢子的毒力，并且缺失这两个基因会使孢子在A/J小鼠中无毒。此外，与AtxA1不同，AtxA2在体外不形成稳定的同多聚体，尽管AtxA1和AtxA2形成异二聚体。我们的数据表明，AtxA1是G9241毒力因子表达的主要调节因子，并且AtxA1和AtxA2都是完全毒力所必需的。
