Abstract
Several mud volcanoes are active in the Canadian Beaufort Sea. In this study, we investigated vertical variations in methanotrophic communities in sediments of the mud volcano MV420 (420 m water depth) by analyzing geochemical properties, microbial lipids, and nucleic acid signatures. Three push cores were collected with a remotely operated vehicle from visually discriminative habitats that were devoid of megafauna and/microbial mats (DM) to the naked eye, covered with bacterial mats (BM), or colonized by siboglinid tubeworms (ST). All MV420 sites showed the presence of aerobic methane oxidation (MOx)- and anaerobic methane oxidation (AOM)-related lipid biomarkers (4α-methyl sterols and sn-2-hydroxyarchaeol, respectively), which were distinctly different in comparison with a reference site at which these compounds were not detected. Lipid biomarker results were in close agreement with 16S rRNA analyses, which revealed the presence of MOx-related bacteria (Methylococcales) and AOM-related archaea (ANME-2 and ANME-3) at the MV420 sites. 4α-methyl sterols derived from Methylococcales predominated in the surface layer at the BM site, which showed a moderate methane flux (0.04 mmol cm−2 y−1), while their occurrence was limited at the DM (0.06 mmol cm−2 y−1) and ST (0.01 mmol cm−2 y−1) sites. On the other hand, 13C-depleted sn-2-hydroxyarchaeol potentially derived from ANME-2 and/or ANME-3 was abundant in down-core sediments at the ST site. Our study indicates that a niche diversification within this mud volcano system has shaped distinct methanotrophic communities due to availability of electron acceptors in association with varying degrees of methane flux and bioirrigation activity.
Highlights
In this study, we provide the first evidence for MOx- and AOM-related methanotrophic communities in connection with chemosynthetic communities at an active MV in the Canadian Beaufort Sea
Phylogenetic trees of major archaeal OTUs of Methanomicrobia, bacterial OTUs of Deltaproteobacteria and Methylococcales of Gammaprotoebacteria with greater than 5% relative abundance (Supplementary Information Sequence 1–3) were constructed using the maximum-likelihood algorithm[91] with the GTR evolutionary model using IQ-TREE92
Our results revealed that niche diversification of methanotrophic communities (i.e., Methylococcales and ANME-2 and ANME-3 groups, respectively) may have been shaped by environmental factors such as availability of electron acceptors and bioirrigation activities by chemosynthetic organisms
Summary
Sediment samples were obtained during the 2017 ARA08C cruise of the Korean icebreaker RV Araon at the Beaufort MV (water depth of 420 m) from different chemosynthetic provinces (ARA08CDIVE105-8 and -9: BO site, ARA08C-DIVE104-7 and-13: BM site, and ARA08C_DIVE105-12 and -14: ST site) using a push core operated by an ROV system and at the reference site (ARA08C-21BC, water depth of 420 m) using a box corer (Fig. 1). Push- and box-core samples were subsampled horizontally with 20 mL serum vials, which were sealed immediately with butyl rubber stoppers to prevent gas exchange and stored at 4 °C. Core sediments were sliced into 1cm sections and subsampled for analysis of bulk elements, lipid biomarkers, and 16S rRNA gene sequences.
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