Genomic characteristics and geographical distribution of uncultivated soil prokaryotes

Abstract Most soil prokaryotic species remain uncultivated, limiting our understanding of the terrestrial microbiome. Metagenomic sequencing, and particularly the study of metagenome-assembled genomes (MAGs), represents an unprecedented opportunity to characterize the genomic features and biogeography of uncultivated prokaryotic taxa at the large scale. Here, we analyze 40,039 genomic bins from cultivated and uncultivated soil taxa within the SMAG catalog, and examine the occurrence of uncultivated prokaryotes in 9,012 metagenomic samples from the Sandpiper resource. Compared to genera with cultivated representatives, uncultivated soil prokaryotes show smaller genomes, lower G + C content, tendency to acidophilic, non-alkaline, thermophilic and host-associated lifestyles, and slower growth rates, with the latter having the highest predictive power for cultivation status. Uncultivated soil microbes also show unique gene repertoires, characterized by a depletion of biosynthetic and motility genes. We also show that completely uncultivated genera are more abundant in tropical and arctic soils, indicating substantial hidden diversity in these regions. Our work emphasizes that current cultivation efforts systematically fail to capture a particular fraction of soil prokaryotic diversity, and provides guidelines for future cultivation strategies.