Sequence and Organization of pXO1, the Large Bacillus anthracis Plasmid Harboring the Anthrax Toxin Genes

Abstract

The Bacillus anthracis Sterne plasmid pXO1 was sequenced by random, “shotgun” cloning. A circular sequence of 181,654 bp was generated. One hundred forty-three open reading frames (ORFs) were predicted using GeneMark and GeneMark.hmm, comprising only 61% (110,817 bp) of the pXO1 DNA sequence. The overall guanine-plus-cytosine content of the plasmid is 32.5%. The most recognizable feature of the plasmid is a “pathogenicity island,” defined by a 44.8-kb region that is bordered by inverted IS1627 elements at each end. This region contains the three toxin genes (cya, lef, and pagA), regulatory elements controlling the toxin genes, three germination response genes, and 19 additional ORFs. Nearly 70% of the ORFs on pXO1 do not have significant similarity to sequences available in open databases. Absent from the pXO1 sequence are homologs to genes that are typically required to drive theta replication and to maintain stability of large plasmids in Bacillus spp. Among the ORFs with a high degree of similarity to known sequences are a collection of putative transposases, resolvases, and integrases, suggesting an evolution involving lateral movement of DNA among species. Among the remaining ORFs, there are three sequences that may encode enzymes responsible for the synthesis of a polysaccharide capsule usually associated with serotype-specific virulent streptococci.

The CodY pleiotropic repressor controls virulence in gram-positive pathogens

“…Both a tripartite toxin encoded by pagA, lef and cya genes, as well as a poly-y-D-glutamate capsule encoded by the cap operon of B. anthracis are needed for host tissue invasion and immune system fighting during proliferation of B. anthracis vegetative bacteria (Mock & Fouet 2001). The toxin component genes are located on pXO1, a 182-kb plasmid (Okinaka et al, 1999). The biosynthetic enzymes for capsule production are encoded by the capBCADE operon located on plasmid pXO2 (Candela et al, 2005).…”

Lineage‐specific plasmid acquisition and the evolution of specialized pathogens in Bacillus thuringiensis and the Bacillus cereus group

“…Bacillus plasmids show great diversity and variety, can be large size and are thought to be involved in many processes (Zheng, Peng, Ruan, & Sun, 2013;Zheng et al, 2015Zheng et al, , 2017. Importantly, several characteristic and essential virulence factors are encoded on plasmids in B. cereus sensu lato, a group which includes B. cereus sensu stricto (Bc), Bt, Ba and which is collectively referred to as the B. cereus group (Gonzalez, Brown, & Carlton, 1982;Okinaka et al, 1999).…”

The roles of AtxA orthologs in virulence of anthrax‐like Bacillus cereus G9241

“…Strains of B. anthracis harbor two virulence plasmids, pXO1 and pXO2, that play critical roles in anthrax disease. The plasmid pXO1 contains the genes pagA, lef, and cya that encode the anthrax toxin components protective antigen (PA), lethal factor (LF), and edema factor (EF), respectively (Vodkin and Leppla, 1983;Robertson and Leppla, 1986;Tippetts and Robertson, 1988;Okinaka et al, 1999). The plasmid pXO2 contains the genes necessary for production of a poly-g-D-glutamic acid capsule (Makino et al, 1988).…”