Ammonia oxidizers offset acidification stress via adaptive substrate affinity in aquatic ecosystems

Area of Science:

• Environmental microbiology
• Biogeochemical cycles
• Microbial adaptation

Background:

• Ammonia oxidation is a crucial process in the nitrogen cycle.
• Aquatic acidification shows varied effects on ammonia oxidation, with mechanisms unclear.
• Understanding these responses is vital for predicting ecosystem changes.

Purpose of the Study:

• To investigate the adaptive mechanisms of ammonia-oxidizing microorganisms to aquatic acidification.
• To reconcile conflicting observations regarding ammonia oxidation rates under acidification.
• To establish a framework for predicting nitrogen cycle dynamics under future environmental conditions.

Main Methods:

• pH manipulation experiments across diverse aquatic ecosystems.
• Utilizing a model ammonia-oxidizing archaea species, Nitrosopumilus maritimus strain SCM1.
• Incorporating microbial substrate affinity responses into ecological models.

Main Results:

• Acidification induces a compensatory increase in substrate affinity in ammonia-oxidizing microorganisms.
• This adaptation is more pronounced in ammonia-oxidizing archaea than bacteria.
• Archaea-dominated systems maintain or increase oxidation rates under moderate acidification, while bacteria-dominated systems decline.
• Models incorporating substrate affinity accurately reconcile previous field observations.

Conclusions:

• Regulation of substrate affinity is a key factor in microbial resilience to acidification.
• This adaptive mechanism explains divergent responses in archaea- and bacteria-dominated systems.
• Provides a predictive framework for nitrogen cycle dynamics under ongoing ocean acidification.