Acetate Synthesis from H(2) plus CO(2) by Termite Gut Microbes

Area of Science:

• Microbiology
• Insect Physiology
• Biochemistry

Background:

• Termites rely on hindgut fermentation for nutrient acquisition.
• Acetate is a primary energy source for termites, derived from hindgut fermentation.
• The specific microbial pathways for acetate production from CO2 in termites are not fully elucidated.

Purpose of the Study:

• To investigate the role of gut microbiota in synthesizing acetate from carbon dioxide (CO2) and hydrogen (H2) in termites.
• To determine the contribution of H2-CO2 acetogenesis to the overall acetate production in termite hindgut fermentation.
• To identify the microbial agents responsible for H2-CO2 acetogenesis in termite guts.

Main Methods:

• In vitro incubation of termite gut microbiota with H2 and CO2.
• Quantification of acetate and other fermentation products using gas chromatography.
• Inhibition studies using specific chemicals and antibacterial drugs.
• Microbial defaunation experiments.
• Isolation and characterization of pure bacterial cultures.

Main Results:

• Gut microbiota from Reticulitermes flavipes catalyzed H2-dependent acetate synthesis from CO2 at significant rates.
• This H2-CO2 acetogenesis accounted for approximately one-third of the total acetate produced during hindgut fermentation.
• Acetogenesis was inhibited by oxygen and specific chemicals, and abolished by antibacterial drugs, indicating bacterial involvement.
• H2-CO2 acetogenesis was observed across multiple termite species and in the wood-eating cockroach Cryptocercus punctulatus.
• Pure cultures of H2-CO2-acetogenic bacteria were isolated from Nasutitermes nigriceps.

Conclusions:

• CO2 reduction to acetate via H2-CO2 acetogenesis is a major electron sink pathway in termite hindgut fermentation.
• Bacterial symbionts are the primary agents responsible for H2-CO2 acetogenesis in termites.
• This microbial process provides a substantial fraction of the termites' principal energy source, acetate.