FIG. 3.
The ratio of nonsynonymous to synonymous nucleotide polymorphisms (πa/πs) reveals different patterns of evolution for NADase-active and NADase-inactive strains. The ratios of nonsynonymous to synonymous polymorphisms (πa/πs) of the concatenated internal fragments of the seven housekeeping genes (HK), spn, and ifs are presented for comparison. Strains with NADase activity and strains without NADase activity are compared. Only ifs from the NADase-inactive strains has a ratio consistent with a nonfunctional gene, while spn remains relatively conserved despite the loss of NADase activity.