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 producin g 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 freque ncy dependence, where the likelihood of successful colicin invasion in to a population increases as the initial density of colicinogenic cell s increases. We then incorporate thoughts on the evolution of chromoso mal resistance to colicins and describe how resistance might influence the dynamics of colicinogen invasion and maintenance and the resultin g colicin diversity. The final section deals with a genetic and phylog enetic characterization of colicins and a discussion of the evolutiona ry mechanisms responsible for generating colicin diversity, In this fi nal section we provide details of the different molecular mechanisms k nown to play a role in generating colicin diversity, including the two most dominant forces in colicin evolution: recombination and positive , diversifying, selection.