Atribacteria Reproducing over Millions of Years in the Atlantic Abyssal Subseafloor

Abstract

The deep subseafloor sedimentary biosphere is one of the largest ecosystems on Earth, where microbes subsist under energy-limited conditions over long timescales. It remains poorly understood how mechanisms of microbial metabolism promote increased fitness in these settings. We discovered that the candidate bacterial phylum “ Candidatus Atribacteria” dominated a deep-sea subseafloor ecosystem, where it exhibited increased transcription of genes associated with acetogenic fermentation and reproduction in million-year-old sediment. We attribute its improved fitness after burial in the seabed to its capabilities to derive energy from increasingly oxidized metabolites via a bacterial microcompartment and utilize a potentially reversible Wood-Ljungdahl pathway to help meet anabolic and catabolic requirements for growth. Our findings show that “ Ca . Atribacteria” can perform all the necessary catabolic and anabolic functions necessary for cellular reproduction, even under energy limitation in anoxic sediments that are millions of years old.