Hydrocarbon Cycling in the Tokamachi Mud Volcano (Japan): Insights from Isotopologue and Metataxonomic Analyses

Abstract

Understanding hydrocarbon cycling in the subsurface is important in various disciplines including climate science, energy resources and astrobiology. Mud volcanoes provide insights into biogeochemical processes occurring in the subsurface. They are usually associated with natural gas reservoirs consisting mainly of methane and other hydrocarbons as well as CO2. Stable isotopes have been used to decipher the sources and sinks of hydrocarbons in the subsurface, although the interpretation can be ambiguous due to the numerous processes involved. Here we report new data for hydrocarbon isotope analysis, including position-specific isotope composition of propane, for samples from the Tokamachi mud volcano area, Japan. The data suggest that C2+ hydrocarbons are being biodegraded, with indirect production of methane (“secondary methanogenesis”). Data from chemical and isotopic composition are discussed with regard to 16S rRNA analysis, which exhibits the presence of hydrogenotrophic and acetoclastic methoanogens. Overall, the combination of isotopologue analysis with 16S rRNA gene data allows refining of our understanding of hydrocarbon cycling in subsurface environments.

Recent and episodic activity of decoupled mud/fluid discharge at Sartori mud volcano in the Calabrian Arc, Mediterranean Sea

“…The deepest samples from GC01 and GC38 plot close to the field representative of methane originating from secondary microbial Frontiers in Earth Science frontiersin.org sources, which are based on methanogenic petroleum biodegradation (Milkov and Etiope, 2018). The presence of secondary microbial methane has also been proposed for submarine and terrestrial MVs in other regions (Stadnitskaia et al, 2008;Etiope et al, 2009;Gilbert et al, 2022). For Sartori MV, stable C isotope signatures of CO 2 , which would provide better information on the presence of secondary microbial methane (Milkov and Etiope, 2018), are not available.…”

Acetylene Tunes Microbial Growth During Aerobic Cometabolism of Trichloroethene

“…COMET1 contained a variety of amplicon sequence variance (ASVs) with known TCE cometabolic capability, including Burkholderiaceae (3.2%), Xanthobacteraceae (0.6%), Comamonadaceae (9.6%), Alcaligenaceae (4.3%), and Mycobacteriaceae (5.5%) (Figure A, No exposure). ,− Additionally, Rhodocyclaceae (13.8%) and Beijerinckiaceae (1.5%) (Figure A, No exposure) were also abundant. Rhodocylclaceae (13.8%) and Beijerinckiaceae (1.5%) can use propane in their energy metabolism but are not known to cometabolize TCE. ,− We expected that exposure to acetylene would decrease the relative abundance of ASVs known to have TCE cometabolic capacity or be able to consume propane. Contrary to expectations, exposure to acetylene for 1, 2, 4, or 8 d did not yield major differences in the relative abundance of the top ten most abundant ASVs when compared to ‘No exposure’ control (Figure A).…”

“…Rhodocylclaceae (13.8%) and Beijerinckiaceae (1.5%) can use propane in their energy metabolism but are not known to cometabolize TCE. 53 , 86 − 88 We expected that exposure to acetylene would decrease the relative abundance of ASVs known to have TCE cometabolic capacity or be able to consume propane. Contrary to expectations, exposure to acetylene for 1, 2, 4, or 8 d did not yield major differences in the relative abundance of the top ten most abundant ASVs when compared to ‘No exposure’ control ( Figure 3 A).…”