Copper availability controls niche differentiation between comammox Nitrospira and ammonia-oxidizing bacteria

Area of Science:

• Environmental microbiology
• Water treatment technologies
• Biogeochemistry

Background:

• Biological oxidation of ammonia (nitrification) is crucial for nitrogen removal in water purification.
• Low copper concentrations often limit nitrification efficiency in drinking water treatment, especially for groundwater sources.
• Copper dosing impacts nitrification rates and the composition of nitrifying microbial communities, but underlying mechanisms are unclear.

Purpose of the Study:

• To investigate the effect of copper availability on the relative abundance of complete ammonia-oxidizing bacteria (comammox) and canonical ammonia-oxidizing bacteria (AOB).
• To explore differences in copper transport mechanisms between comammox and AOB.
• To understand copper's role in shaping microbial communities for engineered water treatment processes.

Main Methods:

• Comparative metagenomic analysis of nitrifying communities in a drinking water treatment plant.
• Laboratory-scale bioreactor experiments manipulating copper concentrations.
• Quantification of comammox and AOB activity using catalyzed reporter deposition-fluorescent in situ hybridization (CARD-FISH).

Main Results:

• Comammox Nitrospira possess high-affinity copper uptake systems (PcoB/CopB), making them competitive in low-copper environments.
• Comammox Nitrospira dominated under copper-limited conditions, whereas AOB were more abundant at high copper concentrations.
• Transcriptional activity of comammox Nitrospira was significantly higher than AOB under copper limitation.

Conclusions:

• Copper availability is a key factor influencing the dominance of comammox versus AOB in nitrification processes.
• Comammox Nitrospira's specialized copper uptake mechanisms confer a competitive advantage in low-copper environments.
• These findings have significant implications for optimizing engineered water treatment processes by managing copper levels to control ammonia-oxidizing guilds.