Metabolic stratification driven by surface and subsurface interactions in a terrestrial mud volcano

Abstract

Terrestrial mud volcanism represents the prominent surface geological feature, where fluids and hydrocarbons are discharged along deeply rooted structures in tectonically active regimes. Terrestrial mud volcanoes (MVs) directly emit the major gas phase, methane, into the atmosphere, making them important sources of greenhouse gases over geological time. Quantification of methane emission would require detailed insights into the capacity and efficiency of microbial metabolisms either consuming or producing methane in the subsurface, and establishment of the linkage between these methane-related metabolisms and other microbial or abiotic processes. Here we conducted geochemical, microbiological and genetic analyses of sediments, gases, and pore and surface fluids to characterize fluid processes, community assemblages, functions and activities in a methane-emitting MV of southwestern Taiwan. Multiple lines of evidence suggest that aerobic/anaerobic methane oxidation, sulfate reduction and methanogenesis are active and compartmentalized into discrete, stratified niches, resembling those in marine settings. Surface evaporation and oxidation of sulfide minerals are required to account for the enhanced levels of sulfate that fuels subsurface sulfate reduction and anaerobic methanotrophy. Methane flux generated by in situ methanogenesis appears to alter the isotopic compositions and abundances of thermogenic methane migrating from deep sources, and to exceed the capacity of microbial consumption. This metabolic stratification is sustained by chemical disequilibria induced by the mixing between upward, anoxic, methane-rich fluids and downward, oxic, sulfate-rich fluids.

Niche specialization of bacteria in permanently ice‐covered lakes of the McMurdo Dry Valleys, Antarctica

“…Bacteria belonging to candidate division WM88 have been detected in various anoxic environments, including hydrothermal vents (Schauer et al ., ), biofilms of sulfur‐rich caves (Macalady et al ., ) and hypersaline microbial mats (Harris et al ., ). Sequences obtained from two WM88 clones (Fryxell_set2 and Fryxell_13) identified in the present study matched most closely to sequences deriving from bacteria collected from a terrestrial mud volcano (98.6–98.8% 16S rRNA gene sequence similarities) (Cheng et al ., ). These sequences were placed into a distinct clade that was separated from other WM88 lineages in the phylogenetic tree.…”

A Post-Genomic View of the Ecophysiology, Catabolism and Biotechnological Relevance of Sulphate-Reducing Prokaryotes

“…Terrestrial mud volcanoes in the South Caspian Basin (Azerbaijan) displayed high SRRs under thermophilic conditions corresponding to the presence of Desulfotomaculum phylotypes; additionally present members of Desulfobacteraceae and Desulfobulbaceae are linked to mesophilic sulphate reduction (GreenSaxena et al, 2012). Based on 16S rRNA gene and metagenomic sequences, members of the Desulfobacterales and Desulfovibrionales are likely to account for sulphate reduction in the shallow, methane-rich zone of a stratified terrestrial mud volcano (SYNHMV) in the Yan-Chou area of southwestern Taiwan (Cheng et al, 2012).…”

Chasing the elusive Euryarchaeota class WSA2: genomes reveal a uniquely fastidious methyl-reducing methanogen

“…However, one potentially class-level Euryarchaeota clade thought to be capable of methanogenesis, WSA2 (or Arc 1), (Hugenholtz 2002;Chouari et al, 2005) remains uncharacterized, despite the identification through 16S ribosomal RNA (rRNA) sequencing more than 15 years ago (Dojka et al, 1998). Moreover, members of this clade have been observed in a wide range of natural and engineered environments (for example, freshwater and marine sediments, contaminated groundwater and bioreactors; Dhillon et al, 2005;Cheng et al, 2012;Saito et al, 2015;Wilkins et al, 2015). To fill this gap in our understanding of methanogen phylogeny and WSA2's potential roles in anaerobic biogeochemical cycles, we construct the first WSA2 genomes through metagenomics of methanogenic bioreactors treating wastewater.…”