Global patterns of subsurface microbial diversity through deep time and space

Abstract

Marine and terrestrial subsurface sediments and rocks are the largest habitat for life on Earth. This deep biosphere harbors an estimated 7x1029microbial cells making up approximately 70% of all prokaryotes on Earth. These microorganisms influence global chemical cycles and may represent an essentially untapped archive of biological diversity and functions. Yet, their community structure, metabolic potential, global diversity, biogeography, and modes of dispersal are largely unknown. Here we compiled and analyzed 757 samples from 40 globally distributed marine and terrestrial subsurface ecosystems representing the largest 16S rRNA gene amplicon dataset of subsurface communities available to date. We also analyzed >150 metagenomes to investigate metabolic capabilities and shed light on essential biogeochemical cycling in these ecosystems. We resolved several hundred microbial genomes spanning many known but little studied phyla of bacteria and archaea. The distribution and variance across these diverse ecosystems is interpreted within the context of a suite of metadata of physicochemical and habitat features. So far we discovered the following major trends: 1. Marine subsurface ecosystems are more diverse than terrestrial subsurface ecosystems 2. The rate of microbial dispersal is higher in marine ecosystems. 3. Although phylogenetic diversity was not exhaustively sampled, the results suggest that we detected most of the gene families that enable life in the subsurface. These findings highlight the metabolic and phylogenetic diversity and longevity of these communities and have major implications for our understanding of microbial dispersal and community assembly over deep time and space.