Genomic Characterization and Copy Number Variation of Bacillus anthracis Plasmids pXO1 and pXO2 in a Historical Collection of 412 Strains
Angela Pena-Gonzalez,
Luis M. Rodriguez-R,
Chung K. Marston,
Jay E. Gee,
Christopher A. Gulvik,
Cari B. Kolton,
Elke Saile,
Michael Frace,
Alex R. Hoffmaster,
Konstantinos T. Konstantinidis
Affiliations
Angela Pena-Gonzalez
School of Biological Sciences, Georgia Institute of Technology, Atlanta, Georgia, USA
Luis M. Rodriguez-R
School of Civil & Environmental Engineering, Georgia Institute of Technology, Atlanta, Georgia, USA
Chung K. Marston
Bacterial Special Pathogens Branch, Division of High-Consequence Pathogens and Pathology, National Center for Emerging and Zoonotic Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, USA
Jay E. Gee
Bacterial Special Pathogens Branch, Division of High-Consequence Pathogens and Pathology, National Center for Emerging and Zoonotic Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, USA
Christopher A. Gulvik
Bacterial Special Pathogens Branch, Division of High-Consequence Pathogens and Pathology, National Center for Emerging and Zoonotic Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, USA
Cari B. Kolton
Bacterial Special Pathogens Branch, Division of High-Consequence Pathogens and Pathology, National Center for Emerging and Zoonotic Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, USA
Elke Saile
Bacterial Special Pathogens Branch, Division of High-Consequence Pathogens and Pathology, National Center for Emerging and Zoonotic Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, USA
Michael Frace
Biotechnology Core Facility Branch, Division of Scientific Resources, National Center for Emerging and Zoonotic Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, USA
Alex R. Hoffmaster
Bacterial Special Pathogens Branch, Division of High-Consequence Pathogens and Pathology, National Center for Emerging and Zoonotic Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, USA
Konstantinos T. Konstantinidis
School of Biological Sciences, Georgia Institute of Technology, Atlanta, Georgia, USA
ABSTRACT Bacillus anthracis plasmids pXO1 and pXO2 carry the main virulence factors responsible for anthrax. However, the extent of copy number variation within the species and how the plasmids are related to pXO1/pXO2-like plasmids in other species of the Bacillus cereus sensu lato group remain unclear. To gain new insights into these issues, we sequenced 412 B. anthracis strains representing the total phylogenetic and ecological diversity of the species. Our results revealed that B. anthracis genomes carried, on average, 3.86 and 2.29 copies of pXO1 and pXO2, respectively, and also revealed a positive linear correlation between the copy numbers of pXO1 and pXO2. No correlation between the plasmid copy number and the phylogenetic relatedness of the strains was observed. However, genomes of strains isolated from animal tissues generally maintained a higher plasmid copy number than genomes of strains from environmental sources (P 400) that were recovered from human, animal, and environmental sources around the world. Our results confirmed the remarkable stability of gene content and synteny of the anthrax plasmids and revealed no signal of plasmid exchange between B. anthracis and pathogenic B. cereus isolates but rather predominantly vertical descent. These findings advance our understanding of the biology and pathogenomic evolution of B. anthracis and its plasmids.
