Gong, Xianzhe

AbstractAsgard archaea were pivotal in the origin of complex cellular life. Hodarchaeales (Asgardarchaeota class Heimdallarchaeia) were recently shown to be the closest relatives of eukaryotes. However, limited sampling of these archaea constrains our understanding of their ecology and evolution1–3, including their anticipated role in eukaryogenesis. Here, we nearly double the number of Asgardarchaeota metagenome-assembled genomes (MAGs) to 869, including 136 new Heimdallarchaeia (49 Hodarchaeales) and several novel lineages. Examining global distribution revealed Hodarcheales are primarily found in coastal marine sediments. Detailed analysis of their metabolic capabilities revealed guilds of Heimdallarchaeia are distinct from other Asgardarchaeota. These archaea encode hallmarks of aerobic eukaryotes, including electron transport chain complexes (III and IV), biosynthesis of heme, and response to reactive oxygen species (ROS). The predicted structural architecture of Heimdallarchaeia membrane-bound hydrogenases includes additional Complex-I-like subunits potentially increasing the proton motive force and ATP synthesis. Heimdallarchaeia genomes encode CoxD, which regulates the electron transport chain (ETC) in eukaryotes. Thus, key hallmarks for aerobic respiration may have been present in the Asgard-eukaryotic ancestor. Moreover, we found that Heimdallarchaeia is present in a variety of oxic marine environments. This expanded diversity reveals these Archaea likely conferred energetic advantages during early stages of eukaryogenesis, fueling cellular complexity.

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. Recent studies using metagenomic techniques have shown the complexity of these communities and identified novel microorganisms from the ocean floor. Here, we obtained 77 metagenome-assembled genomes (MAGs) from the bacterial phylum Armatimonadota in the Guaymas Basin, Gulf of California, and the Bohai Sea, China. These MAGs comprise two previously undescribed classes within Armatimonadota, which we propose naming Hebobacteria and Zipacnadia. They are globally distributed in hypoxic and anoxic environments and are dominant members of deep-sea sediments (up to 1.95% of metagenomic raw reads). The classes described here also have unique metabolic capabilities, possessing pathways to reduce carbon dioxide to acetate via the Wood-Ljungdahl pathway (WLP) and generating energy through the oxidative branch of glycolysis using carbon dioxide as an electron sink, maintaining the redox balance using the WLP. Hebobacteria may also be autotrophic, not previously identified in Armatimonadota. Furthermore, these Armatimonadota may play a role in sulfur and nitrogen cycling, using the intermediate compounds hydroxylamine and sulfite. Description of these MAGs enhances our understanding of diversity and metabolic potential within anoxic habitats worldwide.

AbstractMicrobes in marine sediments play crucial roles in global carbon and nutrient cycling. However, our understanding of microbial diversity and physiology on the ocean floor is limited. Here, we use phylogenomic analyses of thousands of metagenome-assembled genomes (MAGs) from coastal and deep-sea sediments to identify 55 MAGs that are phylogenetically distinct from previously described bacterial phyla. We propose that these MAGs belong to 4 novel bacterial phyla (Blakebacterota, Orphanbacterota, Arandabacterota, and Joyebacterota) and a previously proposed phylum (AABM5-125-24), all of them within the FCB superphylum. Comparison of their rRNA genes with public databases reveals that these phyla are globally distributed in different habitats, including marine, freshwater, and terrestrial environments. Genomic analyses suggest these organisms are capable of mediating key steps in sedimentary biogeochemistry, including anaerobic degradation of polysaccharides and proteins, and respiration of sulfur and nitrogen. Interestingly, these genomes code for an unusually high proportion (~9% on average, up to 20% per genome) of protein families lacking representatives in public databases. Genes encoding hundreds of these protein families colocalize with genes predicted to be involved in sulfur reduction, nitrogen cycling, energy conservation, and degradation of organic compounds. Our findings advance our understanding of bacterial diversity, the ecological roles of these bacteria, and potential links between novel gene families and metabolic processes in the oceans.

Abstract Microbes are the most abundant form of life on Earth and play crucial roles in carbon and nutrient cycling. Despite their crucial role, our understanding of microbial diversity and physiology on the ocean floor is limited. To address this gap in knowledge, we obtained 55 novel bacterial metagenome-assembled genomes (MAGs) from coastal and deep sea sediments. Phylogenomic analyses revealed they belong to four new and one poorly described bacterial phyla. Comparison of their rRNA genes with public databases revealed they are all globally distributed. These novel bacteria are capable of the anaerobic degradation of polysaccharides and proteins, and the respiration of sulfur and nitrogen. These genomes code for an unusually high proportion (~ 9, and up to 20% per genome) of protein families lacking representatives in public databases. Hundreds of these protein families are predicted to be co-localized with genes for sulfur reduction, nitrogen cycling, energy conservation, and the degradation of organic compounds. These findings expand our understanding of microbial diversity and link previously overlooked gene families with key metabolic processes in the oceans.