Nitrification and Nitrifying Bacteria in a Coastal Microbial Mat

Area of Science:

• Microbial Ecology
• Environmental Microbiology
• Biogeochemistry

Background:

• Nitrification, the oxidation of ammonia to nitrite, is a key microbial process in nitrogen cycling.
• This process can be carried out by ammonia-oxidizing archaea (AOA) or ammonium-oxidizing bacteria (AOB).
• Coastal microbial mats represent diverse environments where nitrification dynamics are crucial.

Purpose of the Study:

• To investigate the presence, abundance, and activity of AOA and AOB in three distinct coastal microbial mat types.
• To correlate the abundance and transcription of the amoA gene with potential nitrification rates.
• To understand the environmental factors influencing AOA and AOB community structure and function.

Main Methods:

• Sampling of three structurally different microbial mats along a tidal gradient on the North Sea coast.
• Quantification of AOA and AOB using the amoA gene (abundance and transcription).
• Measurement of potential nitrification rates and analysis of environmental parameters (salinity, ammonium, temperature, nitrate/nitrite).

Main Results:

• Potential nitrification rates varied seasonally, peaking in autumn and lowest in summer.
• Both AOA and AOB were detected in all mat types, with AOB amoA genes being significantly more abundant.
• AOB amoA gene transcription, but not abundance, positively correlated with potential nitrification rates, suggesting AOB are the primary drivers.

Conclusions:

• Ammonium-oxidizing bacteria (AOB) are the main contributors to nitrification in these coastal microbial mats.
• Environmental factors such as salinity, ammonium, temperature, and nitrate/nitrite concentrations influence AOA and AOB communities.
• The activity of AOB, indicated by amoA gene transcription, is a better predictor of nitrification rates than gene abundance alone.