Ammonia leakage can underpin nitrogen-sharing among soil microorganisms

Area of Science:

• Soil microbiology
• Microbial ecology
• Biogeochemical cycling

Background:

• Soil microbial communities are vital for ecological functions like nutrient cycling.
• Interactions between soil microorganisms significantly impact ecosystem stability.
• Mechanisms driving these microbial interactions remain incompletely understood.

Purpose of the Study:

• To investigate nutrient-based interactions between the soil fungus Serendipita indica and bacterium Bacillus subtilis.
• To elucidate the role of nitrogen metabolism in mediating interactions between these two model organisms.

Main Methods:

• Co-culturing experiments with S. indica and B. subtilis using nitrate as the nitrogen source.
• Utilizing a mathematical model to explore pH-dependent ammonia/ammonium dynamics.
• Employing a mutant B. subtilis strain deficient in ammonia uptake.

Main Results:

• S. indica cannot grow on nitrate alone but thrives when co-cultured with B. subtilis.
• B. subtilis utilizes nitrate and releases ammonia, which S. indica assimilates.
• A mathematical model predicted and experiments confirmed that reduced ammonium uptake by B. subtilis enhances ammonia release and S. indica growth.

Conclusions:

• Ammonia-mediated nitrogen sharing (N-sharing) is a significant, previously under-appreciated interaction mechanism in soil.
• This N-sharing process is sensitive to environmental factors like pH and microbial physiology.
• Understanding these interactions is crucial for predicting soil ecosystem functions.