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Bacterial competition: surviving and thriving in the microbial jungle
Michael E. Hibbing*, Clay Fuqua*, Matthew R. Parsek‡ and S. Brook Peterson‡

Abstract | 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 cultureshave 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 studiesand to evaluate the predictions that they generate in more natural settings.
Competitive exclusion
When competition between species results in the elimination of one species from a given habitat or region.

*Department of Biology, Indiana University, Bloomington, Indiana 47405, USA. ‡ Department of Microbiology, University of Washington, Seattle, Washington 98195, USA. Correspondence toM.R.P. and S.B.P. e-mails: parsem@u.washington.edu; snowbp@u.washington.edu doi:10.1038/nrmicro2259 Published online 30 November 2009

Examples of true charity and altruism in human societies are highly lauded, and rightfully so, but they are far from the norm. Competition is a fact of modern life, with individuals and institutions vying to gain advantage in terms of finances, material resources andstatus. In capitalist societies, competition is thought to continually hone the attributes of competing entities, improving their efficiency and defining their activities and structure. The high level of competition in human society in many ways mirrors the comparatively ancient and complex interactions that can be observed at virtually every level in the natural world. The battle for theresources that organisms need in order to survive and pass on genes to the next generation can often be fierce and unforgiving. This leads to natural selection, which provides the driving force for innovation and diversification between competing organisms1. In animals and plants, there are a large number of well-studied examples of populations that are held in balance, or driven to transition, bycompetitive forces. Connell’s barnacles provide a classic example 2. He found that, in intertidal zones in Scotland, Balanus barnacles were always found closest to the shore, whereas Chthamalus barnacles grew further up the rocks. If he removed the Balanus barnacles from the lower areas, Chthamalus could grow there, but on reintroduction of the more competitive Balanus, Chthamalus would eventually becrowded out. However, Balanus could not grow further up the rocks, owing to its desiccation sensitivity. Thus, the habitat of Chthamalus was limited to areas where it could escape from competition with Balanus, in an example of competitive exclusion.

Similarly, most microorganisms face a constant battle for resources. Vast numbers of microorganisms are present in a wide range of differentenvironments. Tremendous microbial diversity has been revealed by new molecular methodologies such as metagenomic sequencing and deep microbial tag sequencing 3,4. These approaches and others have begun to reveal that underlying the numerically dominant microbial populations is a highly diverse, low-abundance population (described as the rare biosphere, see Ref. 3). Members of the rare biosphere that areamplified under favourable conditions to which they are pre-adapted can give rise to discrete, abundant populations. The potential pool of microbial competitors is therefore vast, and a wide range of mechanisms can be responsible for the emergence and radiation of dominant microbial populations. Nutritional resources are a focal point of microbial competition. Jacques Monod, a pioneer in the...
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