Characterization of Saccharimonadia bacteria in Lakes Baikal and Khubsugul: taxonomic and functional diversity

Abstract

Ultra-small bacteria are ubiquitous in the environment, but for some time they have remained out of scientific focus. One of the reasons is their small size. Ultramicrobacteria, which are defined as bacteria with a cell size of less than 0.1 µm³, can pass through a filter with a pore size of 0.2 µm. Moreover, there are some difficulties associated with their cultivation. Currently, relatively pure cultures have been obtained, but mostly for dominant phyla. Rare phyla are represented only by single strains. At the same time, ultramicrobacteria are found in a wide range of environments, and their high-ordered, small genomes and unique physiological features attract the increasing attention of researchers. The development of metagenomics allows us to partially overcome cultivation limitations, and in this article, we present metagenomic assemblies derived from water samples of the largest oligotrophic lakes on the Earth, Baikal (Russian Federation) and Khubsugul (Mongolia). In this study, we carried out the taxonomic and functional analysis of reconstructed genomes of Saccharimonadia class bacteria (phylum Patescibacteria), which is intended to expand our knowledge of rare representatives of microbial communities and supplement the already available information regarding the inhabitants of the oldest ecosystems.