The Ecology and Evolution of Microbial Defense Systems in Escherichia coli

Microbes produce an extraordinary array of microbial defense systems. These include broad-spectrum classical antibiotics critical to human health concerns; metabolic by-products, such as the lactic acids produced by lactobacilli; lytic agents, such as lysozymes found in many foods; and numerous types of protein exotoxins and bacteriocins. The abundance and diversity of this biological arsenal are clear. Lactic acid production is a defining trait of lactic acid bacteria. Bacteriocins are found in almost every bacterial species examined to date, and within a species, tens or even hundreds of different kinds of bacteriocins are produced. Halobacteria universally produce their own version of bacteriocins, the halocins. Streptomycetes commonly produce broad-spectrum antibiotics. It is clear that microbes invest considerable energy in the production and elaboration of antimicrobial mechanisms. What is less clear is how such diversity arose and what roles these biological weapons play in microbial communities. One family of microbial defense systems, the bacteriocins, has served as a model for exploring evolutionary and ecological questions. In this review, current knowledge of how the extraordinary range of bacteriocin diversity arose and is maintained in one species of bacteria, Escherichia coli, is assessed and the role these toxins play in mediating microbial dynamics is discussed.