Phylogenetic Species Concept in Microbiology

The phylogenetic species concept defines a species as the smallest group of organisms that share a common ancestor and have unique genetic traits.

Microbes reproduce asexually, show limited morphological diversity, and engage in horizontal gene transfer. So, traditional species definitions cannot be used.

The phylogenetic species concept is suited for microbial classification, as it compares gene sequences or whole genomes to show evolutionary relationships.

For example, if two DNA sequences have approximately 98.7% similarity in their 16S rRNA gene sequence, they are generally considered to belong to the same species.

Average Nucleotide Identity, or ANI, compares entire genomes and is considered a more accurate method.

A threshold of 95–96% ANI, indicating 95-96% genomic similarity, is widely accepted for species-level identity.

The phylogenetic species concept is usually combined with ecological traits and metabolic features to more accurately define a microbial species.