A theoretical and empirical investigation of the invasion dynamics of colicinogeny

A mathematical model describing the dynamics of a colicinogenic and a colic in-sensitive population propagated under serial transfer culture conditions was formulated. In addition, a series of in vitro invasion experiments usi ng six representatives of the E colicin group was undertaken, together with the estimation of the growth rates and colicinogenic characteristics of th e strains. Growth rates among the strains varied by up to 44%. There were 1 4-fold differences among strains in their lysis rates and there were up to 10-fold differences in the amount of colicin produced per lysed cell. The i n vitro serial transfer invasion experiments revealed that regardless of in itial frequency all colicinogenic strains succeeded in displacing the sensi tive cell populations. The amount of time required for the colicin-sensitiv e cell population to be displaced declined as the initial frequency of the colicinogenic population increased and strains producing higher titres of c olicin tended to displace the sensitive strain more rapidly. Overall, the o bserved dynamics of the invasion of colicinogenic strains was adequately de scribed by the theoretical model. However, despite there being substantial differences among the strains in their growth rates and colicinogenic chara cteristics there were relatively few differences, observed or predicted, in the invasion dynamics of the six colicinogenic strains. These results sugg est that the characteristics of different colicinogenic strains cannot be u sed to explain the extensive variation in the relative abundance of differe nt colicins in natural populations of bacteria.