The ecology and evolution of bacteriocins

In this review we focus on the ecological and evolutionary forces that determine the frequency and diversity of colicins in Escherichia coli, To begin, we describe that this killing phenotype is ubiquitous in E. coli, with as many as 50% of the isolates from a population producing colicin toxins, and that each population sampled has its own unique distribution of the more than 20 known colicin types, Next, we explore the dynamics of colicinogeny, which exhibits a typical form of frequency dependence, where the likelihood of successful colicin invasion into a population increases as the initial density of colicinogenic cells increases. We then incorporate thoughts on the evolution of chromosomal resistance to colicins and describe how resistance might influence the dynamics of colicinogen invasion and maintenance and the resulting colicin diversity. The final section deals with a genetic and phylogenetic characterization of colicins and a discussion of the evolutionary mechanisms responsible for generating colicin diversity, In this final section we provide details of the different molecular mechanisms known to play a role in generating colicin diversity, including the two most dominant forces in colicin evolution: recombination and positive, diversifying, selection.