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Related Experiment Videos

What are bacterial species?

Frederick M Cohan1

  • 1Department of Biology, Wesleyan University, Middletown, Connecticut 06459-0170, USA. fcohan@wesleyan.edu

Annual Review of Microbiology
|July 27, 2002
PubMed
Summary

Bacterial species definitions lack consensus. Research suggests ecotypes, not named species, represent the fundamental unit of bacterial diversity, aligning with universal species concepts.

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Area of Science:

  • Microbiology
  • Evolutionary Biology
  • Systematics

Background:

  • Bacterial systematics lacks a consensus species definition, unlike eukaryotes.
  • Current methods focus on phenotypic/genetic clusters without a guiding species concept.
  • Eukaryotic species concepts involve cohesion, irreversible divergence, and ecological distinctness.

Purpose of the Study:

  • To investigate whether bacterial ecotypes, rather than named species, align with universal species concepts.
  • To explore the applicability of cohesion, irreversible divergence, and ecological distinctness to bacterial populations.
  • To propose a revised understanding of bacterial diversity based on ecotypes.

Main Methods:

  • Utilized universal sequence-based approaches to identify and analyze bacterial populations.
  • Compared the properties of identified ecotypes with universal species concept criteria.
  • Examined the relationship between named bacterial species and discovered ecotypes.

Main Results:

  • Bacterial ecotypes, occupying specific ecological niches, exhibit properties of universal species.
  • These properties include cohesive forces and recurrent purging of divergence by natural selection.
  • Named bacterial species were found to encompass multiple distinct ecotypes.

Conclusions:

  • Bacterial ecotypes, not named species, function as the fundamental unit of biological diversity.
  • Named bacterial species are more analogous to genera due to containing multiple ecotypes.
  • A theory-based species concept for bacteria should focus on ecotypes and their ecological roles.

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