Nitrogen cycling and microbial cooperation in the terrestrial subsurface

Area of Science:

• Environmental microbiology
• Geochemistry
• Biogeochemical cycles

Background:

• The nitrogen cycle is crucial for aquatic ecosystems, yet terrestrial subsurface nitrogen transformations are understudied.
• Understanding microbial responses to varying aquifer chemistries is essential for predicting nitrogen cycling.

Purpose of the Study:

• To investigate how nitrogen-cycling microorganisms in groundwater respond to diverse aquifer chemistries.
• To quantify the prevalence and activity of key nitrogen cycling pathways in groundwater.

Main Methods:

• Sampling of groundwater from 55 sites for gene quantification and 26 sites for transcript quantification.
• Metagenomic and metatranscriptomic analysis of samples from oxic and dysoxic groundwater.
• Quantification of genes and transcripts for major nitrogen cycling pathways.

Main Results:

• Nitrogen cycling mechanisms like ammonia oxidation and denitrification were prevalent and redundant across varying aquifer conditions.
• Simultaneous transcriptional activity of multiple nitrogen cycling pathways (nitrification, denitrification, anammox) was observed, indicating oxic-anoxic interfaces.
• Complete denitrifiers drove significant transcriptional activity, especially in dysoxic conditions, with a focus on energy-efficient N2O reduction.

Conclusions:

• Nitrogen cycling is a core function of aquifer microbial communities, characterized by redundancy and potential for synergistic interactions.
• Groundwater microbial communities exhibit rich metabolic diversity, contributing to significant fixed nitrogen loss.
• Microbial communities prioritize energy efficiency in nitrogen loss pathways, particularly under varying environmental conditions.