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Cohan FM, Perry EB.. A systematics for discovering the fundamental units of bacterial diversity. Curr Biol 17: R373-R386

Department of Biology, Wesleyan University, Middletown, Connecticut 06459-0170, USA.
Current Biology (Impact Factor: 9.92). 06/2007; 17(10):R373-86. DOI: 10.1016/j.cub.2007.03.032
Source: PubMed

ABSTRACT Bacterial systematists face unique challenges when trying to identify ecologically meaningful units of biological diversity. Whereas plant and animal systematists are guided by a theory-based concept of species, microbiologists have yet to agree upon a set of ecological and evolutionary properties that will serve to define a bacterial species. Advances in molecular techniques have given us a glimpse of the tremendous diversity present within the microbial world, but significant work remains to be done in order to understand the ecological and evolutionary dynamics that can account for the origin, maintenance, and distribution of that diversity. We have developed a conceptual framework that uses ecological and evolutionary theory to identify the DNA sequence clusters most likely corresponding to the fundamental units of bacterial diversity. Taking into account diverse models of bacterial evolution, we argue that bacterial systematics should seek to identify ecologically distinct groups with evidence of a history of coexistence, as based on interpretation of sequence clusters. This would establish a theory-based species unit that holds the dynamic properties broadly attributed to species outside of microbiology.

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    • "Driven by positive selection, dnaE2 passes through one bacterium to another (by horizontal gene transfer or recombination), sweeping through different bacterial phyla and triggering new ecological differentiations. This view is consistent with the model of 'ecotype-formation mutations' (Cohan and Perry, 2007). However, significant work remains to be done in order to reveal the detailed genetic basis of these adaptive evolutionary changes. "
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    • "Ecotype formation occurs when an individual changes its ecological niche, thereby releasing itself from the cohesive force of periodic selection within its parental ecotype. Ecotype formation is therefore analogous to sexual isolation and speciation among macroorganisms (8,42). Estimating the rates of periodic selection and ecotype formation therefore can shine light on the evolutionary and ecological processes that drive microbial diversity. "
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    • "Studying in situ diversity of a given group of microbes is indeed problematic and providing a comprehensive study of any type of biological diversity would be complicated beyond feasibility if nearly every individual organism were ecologically unique [30]. "
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