Microbial methane cycling in a terrestrial mud volcano in eastern Taiwan

Area of Science:

• Geomicrobiology
• Biogeochemistry
• Environmental Science

Background:

• Methane cycling in terrestrial mud volcanoes is not well understood.
• Mud volcanoes are significant sources of methane emissions.
• Characterizing microbial communities is crucial for understanding methane biogeochemistry.

Purpose of the Study:

• To investigate microbial communities and methane cycling in onshore mud volcanoes.
• To identify the microbial processes involved in methane transformation.
• To understand the role of metal reduction in methane metabolism.

Main Methods:

• Analysis of bubbling fluids and sediment cores from a Taiwanese mud volcano.
• Pore water chemistry profiling to determine methane and metal concentrations.
• Methane carbon isotope analysis (δ(13)C).
• 16S rRNA gene-based microbial community analysis.

Main Results:

• Methane concentrations increased with depth and varied significantly.
• Methane concentrations correlated inversely with Fe(2+)/Mn(2+) and δ(13)C values, indicating metal-methane transition zones.
• Archaeal communities were dominated by ANME-2a and methylotrophic methanogens.
• Bacterial communities comprised Proteobacteria, Firmicutes, and Bacteroidetes.
• ANME-2a and metal-reducing bacteria populations correlated with metal and methane isotope profiles.

Conclusions:

• A coupling between anaerobic methanotrophy and metal reduction occurs in metal-methane transition zones under sulfate-deficient conditions.
• This metabolic strategy differs from that observed in marine cold seeps.
• Anaerobic methanotrophs consume both in situ produced and deep-sourced methane.
• Microbial processes in different depth intervals quantitatively and isotopically alter methane before atmospheric emission.