Table 1 Natural selection analysis. The mean of p values for all the comparisons among all yaaW and htgA homologs plus standard deviations, SD. * p < 0.05; ** p < 0.01. Neutrality: a statistically significant p value indicates non-neutral evolution; Purifying selection: a statistically significant p value indicates purifying selection

yaaW (all sequences)

0.042 ± 0.1215 *

0.024 ± 0.0869 *

A versus B

2.079E-09 ± 1.6218E-09 **

1.168E-09 ± 6.5436E-10 **

A versus O

0.009 ± 0.0266 **

0.005 ± 0.0139 **

B versus O

0.031 ± 0.0696 *

0.015 ± 0.0337 *

htgA (all sequences)

0.116 ± 0.2171

0.068 ± 0.1456

A versus B

6.69E-06 ± 8.3638E-06 **

2.378E-06 ± 3.0695E-06**

A versus O

0.118 ± 0.2358

0.057 ± 0.1187

B versus O

0.097 ± 0.2122

0.050 ± 0.1050