Genomes reveal the cohesiveness of bacterial species taxa and provide a path towards describing all of bacterial diversity.

Abstract This book chapter argues that bacterial systematists of the mid-20th century fortuitously created a species-level systematics that actually fits an important universal theory of speciation by discussing taxonomy would allow us to infer the important characteristics of any unknown organism once we classify it to species. It turns out, unexpectedly, that bacterial species taxa share a species-like property with the species taxa of zoology and botany. While recombination within species taxa of all these groups fails to prevent diversification within species, recombination nevertheless appears to act universally as a force of cohesion within species taxa. That is, recurrent recombination within species limits neutral sequence divergence within species taxa of plants, animals, and bacteria; recombination also allows a sharing of generally adaptive genes across a species range. The 95% ANI criterion that demarcates the traditionally defined species taxa of bacteria fortuitously also yields groups of bacteria that are subject to the species-like property of cohesion, where recombination prevents neutral sequence divergence among ecotypes within a species. Use of the ANI criterion, then, not only provides an easily used algorithm for demarcating bacterial species; it also places bacterial demarcation on the same theory-based foundation as the species taxonomy of animals and plants.