A Putatively Denitrifying Anaerobic Methanotroph from South Africa's Deep Biosphere Belonging to Candidate Phylum Bathyarchaeota
Abstract
The Bathyarchaeota (formerly known as the Miscellaneous Crenarchaeotal Group) are an evolutionarily diverse and cosmopolitan phylum in the deep biosphere, often representing a significant fraction of archaeal diversity. Though a pure culture isolate remains elusive, diverse metabolic capabilities such as acetogenesis, fermentation, methanogenesis, and denitrification have been suggested by isotopic, lipidomic, and metagenomic studies. The dissimilatory anaerobic oxidation of methane (AOM) has previously been suggested in the Bathyarchaeota but has yet to be directly evidenced by laboratory or bioinformatic analyses.
Metagenomic sequencing of fracture fluid from the BE326-BH2 borehole located 1.39 km below land surface in South Africa's Beatrix Gold Mine has yielded a nearly complete (89.8%), low-contamination (3.7%) metagenome-assembled genome (MAG) of a Bathyarchaeota archaeon. This Bathyarchaeota MAG contains a nearly complete pathway for hydrogenotrophic and acetoclastic methanogenesis, a partial reductive tricarboxylic acid cycle, and complete dissimilatory nitrate reduction. 16S rRNA gene analysis places this MAG (hereafter BE326-BA-RLH) in the Bathyarchaeota subgroup MCG-A. The gene encoding for methyl coenzyme reductase subunit A (mcrA) is missing from BE326-BA-RLH, but a short (265 bp) mcrA contig belonging to a deeply branched clade sister to Bathyarchaeota mcrA was discovered in the community metagenome assembly. Analyses of GC content and variance in tetranucleotide frequency do not rule out the possibility that this mcrA belongs to BE326-BA-RLH, but the contig is too short to be binned to the MAG without significantly increasing contamination. Nonetheless, given the bi-directionality of enzymes involved in methanogenesis, whose reversal is thermodynamically favored under the high pCH4 conditions observed in situ at BE326-BH2 (upwards of 90% of dissolved gases), we propose the possibility that BE326-BA-RLH may be capable of coupling AOM with dissimilatory nitrate reduction in the studied borehole. This study provides further support that members of Bathyarchaeota may perform AOM.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.B43F..14H
- Keywords:
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- 0428 Carbon cycling;
- BIOGEOSCIENCES