Nitrate and ammonia as nitrogen sources for deep subsurface microorganisms.
Heini Kutvonen1, Pauliina Rajala2, Leena Carpén2
1Material Recycling and Geotechnology, VTT Technical Research Centre of Finland Espoo, Finland.
Frontiers in Microbiology
|November 4, 2015
Summary
This study reveals that specific bacteria, like Burkholderiales and Rhizobiales, are crucial for nitrogen cycling in deep Finnish bedrock groundwater, even when present in low numbers. Their activity was confirmed using stable isotope probing.
Area of Science:
- Microbiology
- Environmental Science
- Geochemistry
Background:
- Nuclear waste repositories require understanding microbial communities in deep anoxic environments.
- Nitrogen cycling is a critical biogeochemical process in subsurface ecosystems.
Purpose of the Study:
- To investigate the N-utilizing bacterial community in anoxic brackish groundwater of a nuclear waste repository.
- To identify key microbial players and their roles in the nitrogen cycle at 100 m depth.
Main Methods:
- Utilized (15)N-based stable isotope probing (SIP) combined with enrichment experiments.
- Incubated groundwater samples with (14/15)N-ammonium or (14/15)N-nitrate, with or without methane.
- Analyzed bacterial 16S rRNA, nitrate reductase (narG), and ammonia monooxygenase (amoA) gene abundance and diversity.
Main Results:
- Substrate amendment increased bacterial gene copies but decreased overall diversity.
- Hydrogenophaga/Malikia, Methylobacter, and Sulfuricurvum were enriched under specific conditions.
- Minority bacterial clades (Burkholderiales, Rhizobiales) utilized (15)N from ammonium and nitrate, indicating significant ecological roles.
Conclusions:
- Specific bacterial groups, despite low abundance, play vital roles in the groundwater nitrogen cycle.
- Substrate availability significantly influences microbial community structure and function in this deep subsurface environment.
- Findings contribute to understanding microbial ecology in engineered subsurface environments like nuclear waste repositories.
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