Characterizing the Uncultivated Microbial Minority: towards Understanding the Roles of the Rare Biosphere in Microbial Communities

Abstract

Microbial communities are frequently numerically dominated by just a few species. Often, the long "tail" of the rank-abundance plots of microbial communities constitutes the so-called "rare biosphere," microorganisms that are highly diverse but are typically found in low abundance in these communities. Their presence in microbial communities has only recently become apparent with advances in high-throughput sequencing technologies. Despite their low numbers, they are thought to play important roles in their communities and may function as potential members to keep the communities intact and resilient. Their phylogenetic diversity also means that they are important subjects for better understanding the interplay between microbial diversity and evolution. I propose that more efforts should be put into characterizing these poorly understood and mostly unknown microbial lineages that hold vast potentials for our understanding of microbial diversity, ecology, and evolution of life on this planet.

Keywords: diversity; ecology; evolution; microbial; microbial ecology; microbial evolution; rare biosphere.

FIG 1

Word cloud and rank-abundance plots of archaeal, bacterial, and eukaryal phyla identified in the Silva database release 138.1. Word clouds were created from taxonomic classification of the nonredundant 16S rRNA sequences obtained from the Silva database. Note that only one out of every two bacterial phyla is shown in the figure.

FIG 2

Word cloud and rank-abundance plots of archaeal and bacterial phyla identified in the Genome Taxonomy Database (GTDB). Word clouds were created from GTDB taxonomic classification of curated genomes used in the database. Note that only one out of every three bacterial phyla is shown in the figure.