Microbial malaise: how can we classify the microbiome?

Abstract

The names and lineages of microorganisms are critical to our understanding of the microbiome. However, microbial taxonomy and phylogeny are in perpetual flux, with emerging criteria being used to rename and reshape our views of the microbial world. Different candidate molecular and nonmolecular criteria are often broadly consistent with one another, which underpins the pluralistic approach to taxonomy. However, the taxonomic picture is clouded when underlying criteria are not in agreement, or when reference datasets contain erroneously named organisms. How does the shifting taxonomic landscape impact our interpretation of microbial communities, especially in the face of inconsistencies and errors? How can taxonomy be applied in a consistent way when different users have different requirements of the classifications that emerge? The key path forward involves finding ways to integrate conflicting taxonomic criteria, choosing the right units of analysis for microbiomic studies, and making molecular taxonomy transparent and accessible in a way that complements current genomic resources.

Keywords: 16S ribosomal RNA gene; Clostridium; genomes; microbiome; operational taxonomic units; taxonomy.