Gut Microbiota Represent a Major Thermogenic Biomass

Area of Science:

• Microbiology
• Metabolic Physiology
• Animal Science

Background:

• Microbial metabolites influence host energy flux, but the energy use of gut microbes themselves is poorly understood.
• Standard respirometry methods cannot measure anaerobic energy flux from gut microbiota.

Purpose of the Study:

• To quantify the energy utilization of gut microbial biomass.
• To assess the impact of reduced gut biomass on host energy expenditure.

Main Methods:

• Surgical reduction of gut biomass (cecectomy) in C57BL/6J mice.
• Assessment of energy expenditure using bomb and direct calorimetry, sensitive to anaerobic flux.
• Evaluation of heat dissipation changes under anesthesia and effects of microbiome-modifying interventions.

Main Results:

• Cecectomy accelerated weight gain, indicating reduced host plus microbial energy expenditure and increased energy efficiency.
• Immediate changes in heat dissipation were observed post-cecectomy, modifiable by microbiome interventions.
• These anaerobic energy flux effects were undetectable by standard O2/CO2 respirometry.

Conclusions:

• The cecum, despite being ~1% of body mass, accounts for ~8% of resting energy expenditure.
• This energy contribution is primarily anaerobic and significantly influenced by microbial composition and abundance.
• Gut microbial biomass plays a crucial, measurable role in host energy flux beyond metabolite production.