Abstract

The hydrocarbon-enriched environments, such as oil reservoirs and oil sands tailings ponds, contain a broad diversity of uncultured microorganisms. Despite being one of the few prokaryotic lineages that is consistently detected in both production water from oil reservoirs and stable hydrocarbon-degrading enrichment cultures originated from oil reservoirs, the physiological and ecological roles of candidate phylum “Atribacteria” (OP9/JS1) are not known in deep subsurface environments. Here, we report the expanded metabolic capabilities of Atribacteria as inferred from genomic reconstructions. Seventeen newly assembled medium-to-high-quality metagenomic assembly genomes (MAGs) were obtained either from co-assembly of two metagenomes from an Alaska North Slope oil reservoir or from previous studies of metagenomes coming from different environments. These MAGs comprise three currently known genus-level lineages and four novel genus-level groups of OP9 and JS1, which expands the genomic coverage of the major lineages within the candidate phylum Atribacteria. Genes involved in anaerobic hydrocarbon degradation were found in seven MAGs associated with hydrocarbon-enriched environments, and suggest that some Atribacteria could ferment short-chain n-alkanes into fatty acid while conserving energy. This study expands predicted metabolic capabilities of Atribacteria (JS1) and suggests that they are mediating a key role in subsurface carbon cycling.

Highlights

  • Atribacteria is a candidate phylum that has been recently proposed to be inclusive of JS1 and OP9 lineages [1, 2]

  • Most of the Atribacteria-like metagenomic assembly genomes (MAGs) in this study do not contain 16S rRNA gene sequences (Supplementary Fig. S1), and the phylogeny of these MAGs was mainly inferred from genome trees and average amino acid identity (AAI) using standards for taxa descriptions of uncultivated microorganisms proposed recently

  • The newly assembled high-quality and medium-quality MAGs reported in this study enable metabolic insight into the previously unknown lineages of JS1-4, JS1-5, JS1-6, JS1-7 and OP-3, and enlarge the current understanding about JS1-1 and JS1-2 lineages

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Summary

Introduction

Atribacteria is a candidate phylum that has been recently proposed to be inclusive of JS1 and OP9 lineages [1, 2]. Members from JS1 and OP9 are widely distributed in both the terrestrial and marine subsurface, including geothermal springs [3], anaerobic marine sediments [4, 5], petroleum reservoirs [6, 7], and brackish waters [8]. Recent studies based on culture-independent genomics have attempted to answer this question. Metabolic reconstruction suggested an anaerobic lifestyle for members of the OP9 lineage based on (hemi)cellulose fermentation through the Embden-Meyerhof glycolysis pathway with hydrogen, acetate and ethanol production in thermal environments. In contrast to the OP9 lineage represented by “Ca. Caldatribacterium” spp., Atribacteria members from the JS1-1 and JS1-2

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