Copy number estimation for Bacillus anthracis plasmids pXO1 and pXO2. Copy number estimation for Bacillus anthracis plasmids pXO1 and pXO2. (A) Plasmid copy number distribution calculated for strains carrying one or both plasmids. B. anthracis cells maintain an estimated average of 3.86 copies of plasmid pXO1 and 2.29 copies of plasmid pXO2, indicating a general pattern where the copy number of pXO1 is nearly twice (1.68×) that of pXO2. (B) Correlation analysis of pXO1 and pXO2 estimated copy numbers showed a high degree of linear positive correlation (Pearson’s r = 0.68, Spearman’s ρ = 0.62). The red line indicates the estimated linear regression model, and the dashed blue lines depict the upper and lower confidence intervals at 95%. Angela Pena-Gonzalez et al. mSystems 2018; doi:10.1128/mSystems.00065-18