microtaxa

Microtaxa is a term used in ecology and microbiology to describe small or low-abundance taxonomic groups within a community. It is not an official rank in biological nomenclature; rather, it serves as a descriptive label for taxa that occupy minor relative abundances in a sample but may have outsized ecological roles. The concept is widely used in studies of microbial communities, where tiny fractions of sequences can correspond to bacteria, archaea, fungi, or protists that are nonetheless persistent or responsive to environmental changes.

Identification and measurement of microtaxa typically rely on high-throughput sequencing of marker genes, such as 16S rRNA or ITS regions, analyzed as amplicon sequence variants (ASVs) or operational taxonomic units (OTUs). Because their abundance is often very low, detecting microtaxa requires deep sequencing, careful quality control, and robust statistical analysis. Taxonomic resolution varies, so microtaxa may be annotated only at the genus or, less often, species level.

Ecological significance and challenges: Microtaxa can contribute to ecosystem processes, act as reservoirs of genetic diversity, or become more prominent after disturbances. However, their small numbers make them susceptible to sampling bias, sequencing errors, and misassignment. Distinguishing true microtaxa from artifacts requires replication, appropriate controls, and careful data processing. The term is commonly used alongside other descriptors such as the rare biosphere or low-abundance taxa.

Notes and alternatives: The use of microtaxa is informal; some researchers prefer explicit descriptors like low-abundance taxa or rare biosphere. The concept highlights the importance of considering diversity beyond the most abundant community members in ecological and microbiological studies.