Ammonia-oxidizing bacteria and archaea exhibit differential nitrogen source preferences.

Area of Science:

• Microbiology
• Environmental Science
• Biogeochemistry

Background:

• Ammonia-oxidizing microorganisms (AOM) are key players in global nitrogen cycling.
• Four main AOM lineages (AOA, β-AOB, γ-AOB, comammox) compete for ammonia, a primary nitrogen substrate.
• Many AOM can also metabolize urea, but how this impacts their ecology is unclear.

Purpose of the Study:

• To investigate the coordination of ammonia and urea metabolism in different AOM lineages.
• To understand how differential substrate utilization influences AOM ecology and coexistence.

Main Methods:

• Stable isotope tracing
• Enzyme kinetics assays
• Transcriptomics

Main Results:

• Ammonia-oxidizing archaea (AOA) and comammox preferentially use ammonia over urea.
• Beta-proteobacterial ammonia-oxidizing bacteria (β-AOB) favor urea, repressing ammonia transport in its presence.
• Gamma-proteobacterial ammonia-oxidizing bacteria (γ-AOB) co-utilize both ammonia and urea.

Conclusions:

• AOM lineages exhibit distinct regulatory strategies for ammonia and urea metabolism.
• These contrasting strategies minimize direct substrate competition, facilitating niche adaptation and coexistence.
• Metabolic flexibility in nitrogen substrate utilization is crucial for understanding microbial community structure in nitrogen cycling.