Thermal-stability and growth-rate effects of all seven mutations.

We measured the effects of beneficial mutations gained under a two-stage selection scheme that naturally induces a two-component fitness, which consists of a growth rate and a decay rate (stability). (A) For visual clarity, we plotted , , and for growth, decay, and fitness effects. Overall, under the heat-shock conditions, the four unique heat-shock mutations improved growth rate, decay rate, and overall fitness relative to the ancestor genotype, ID8. The three unique low-pH mutations improved growth rate but worsened decay rate relative to the ancestor. (B) The circle plots assume an optimal decay rate of zero and an optimal growth rate of 29 (the highest we have ever seen for this family of phages) [39]. Inside the curve is beneficial overall. Inside the dotted lines is beneficial for both traits. All of the heat-shock mutations were beneficial for both traits relative to the ancestor under heat-shock conditions, but the effect for T1 was nonsignificant for .