Expansion of Armatimonadetes through marine sediment sequencing reveals three classes with unique ecological roles

Abstract

Marine sediments comprise one of the largest environments on the planet, and their microbial inhabitants are significant players in global carbon and nutrient cycles. With the advent of improved sampling techniques, recent scientific studies have shown the complexity of these communities and identified novel microorganisms from the ocean floor. Here we add to our understanding of understudied microbes by obtaining 77 metagenome-assembled genomes from the bacterial phylum Armatimonadetes in the Guaymas Basin, Gulf of California, and the Bohai Sea, coastal China. Seven of these MAGs are not classified at the class level. Thus, we propose to name these organisms Zipacnadia. Searches of public databases revealed that the 77 Armatimonadetes described in this study (including Zipacnadia) are globally distributed in hypoxic and anoxic environments and are dominant members of deep-sea sediments (up to 1.95% of the GB metagenomic raw reads). The Armatimonadetes described here also have unique metabolic capabilities for this phylum. They have pathways to reduce CO₂ to acetate via the Wood-Ljungdahl pathway (WLP) and generate energy through the oxidative branch of the Embden-Meyerhof-Parnas pathway using CO2 as an electron sink, maintaining the redox balance via WLP. Some of these organisms may also have an autotrophic lifestyle not previously identified in Armatimonadetes. Furthermore, these Armatimonadetes may play a role in sulfur and nitrogen cycling, using the intermediate compounds hydroxylamine and sulfite. The description of the Armatimonadetes identified in this study enhances our understanding of the diversity and metabolic potential of anoxic habitats worldwide.Marine Scienc