Commensal S. epidermidis has an open pan-genome. Pan-genome size of S. epidermidis. (a) Gene accumulation curves for pan-genome (squares) and core-genome (circles) as a function of genomes sequenced (N). Error bars are ±1 standard deviation for the 100 simulations. Core gene data are fit by: y = a·exp-N/b + c. Pan-genome data are fit by: y = a·Nb + c. (b) Partitioning of core and variable genes for each COG. COGs significantly enriched (P < 0.05, Fisher exact test) in variable or core genes are marked with single and double asterisks, respectively. The dashed line indicates the expected proportions.