Termite gas emissions select for hydrogenotrophic microbial communities in termite mounds

Area of Science:

• Microbiology
• Environmental Science
• Biogeochemistry

Background:

• Organoheterotrophs dominate soils, but atmospheric hydrogen (H₂) levels are usually too low for hydrogenotrophic growth.
• Termite guts produce high H₂ fluxes via fermentation, creating unique microenvironments in soil-derived termite mounds.

Purpose of the Study:

• To investigate the microbial community composition and activity in termite mounds concerning hydrogen (H₂) metabolism.
• To determine if termite emissions shape microbial communities and influence H₂ cycling in soil ecosystems.

Main Methods:

• Community profiling, metagenomic sequencing, and biogeochemical analysis of termite mounds and surrounding soils.
• In situ and ex situ measurements of H₂ oxidation rates and microbial activity.
• Genomic analysis to identify genes related to H₂ uptake and carbon fixation.

Main Results:

• Termite mounds host diverse hydrogenotrophic Actinobacteriota and Dormibacterota, distinct from surrounding soils.
• Genes for H₂ uptake (hydrogenase) and chemosynthesis (RuBisCO) were significantly enriched in mounds.
• High H₂-oxidizing bacterial activity in mounds efficiently consumed termite-derived H₂ and acted as net atmospheric H₂ sinks.
• Termite activity strongly correlated with H₂ oxidation rates across different termite species.
• Methane was produced but not efficiently consumed, with mounds acting as net methane sources.

Conclusions:

• Termite emissions create a responsive terrestrial sink for H₂, driven by specialized microbial communities.
• H₂ availability is a key factor shaping microbial community structure and function in these unique environments.
• A novel arthropod-bacteria interaction involving H₂ transfer between symbiotic and free-living microbes was revealed.