Bacterial competition: surviving and thriving in the microbial jungle

Key Points As has been studied extensively for macroorganisms, competition between and within microbial species constitutes a crucial facet of microbial life in the environment. Individuals in a population of a single bacterial species will be in competition with each other when nutrients are limiting. If the ecological opportunity arises (such as when populations are grown in a spatially structured environment, providing multiple niches), intraspecies competition can lead to selection for the diversification of a bacterial population. Under some conditions, cooperation among individuals in a bacterial population can facilitate competition between groups. However, cooperation can be vulnerable to cheating. Bacteria engage in diverse active competitive strategies. These include: accumulating and storing specific nutrients, thereby depriving potential competitors; blocking access to favourable habitats (such as binding sites on a surface) or forcing the dispersal of competitors; motility, especially when directed (chemotaxis); producing antimicrobial toxins; and interfering with competitors' signalling. Microbial systems should be exploited further for testing ecological theories of competition. Additionally, new technologies should aid in moving the study of bacterial competition from the test tube to the natural habitats of microorganisms. In the diverse microbial communities that are found in most natural environments, bacteria compete with their neighbours for space and resources. Here, the authors review the many active mechanisms that bacteria use to kill or impair their intra- and interspecies competitors. Most natural environments harbour a stunningly diverse collection of microbial species. In these communities, bacteria compete with their neighbours for space and resources. Laboratory experiments with pure and mixed cultures have revealed many active mechanisms by which bacteria can impair or kill other microorganisms. In addition, a growing body of theoretical and experimental population studies indicates that the interactions within and between bacterial species can have a profound impact on the outcome of competition in nature. The next challenge is to integrate the findings of these laboratory and theoretical studies and to evaluate the predictions that they generate in more natural settings.