Abstract

The earth contains a huge number of largely uncharacterized Bacteria and Archaea. Microbiologists are struggling to summarize their genetic diversity and classify them, which has resulted in heated debates on methods for defining species, mechanisms that lead to speciation and whether microbial species even exist. This Review proposes that decisions on the existence of species and methods to define them should be guided by a method-free species concept that is based on cohesive evolutionary forces. It summarizes current approaches to defining species and the problems of these approaches, and presents selected examples of the population genetic patterns at and below the species level.

Author affiliations

1. Environmental Research Institute, University College Cork, Ireland and Department of Molecular Biology, Max-Planck Institut für Infektionsbiologie, 10117 Berlin, Germany.
2. Department of Microbial Ecology, Faculty of Life Sciences, Vienna Ecology Centre, University of Vienna, A-1090 Vienna, Austria.

Correspondence to: Mark Achtman¹ Email: m.achtman@ucc.ie

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