Nitrogen fixation in distinct microbial niches within a chemoautotrophy-driven cave ecosystem.
Mahesh S Desai1, Karoline Assig, Sharmishtha Dattagupta
1Courant Research Center Geobiology, Georg-August-Universität Göttingen, Göttingen, Germany.
The ISME Journal
|August 9, 2013
Summary
This study reveals nitrogen fixation occurs in dark Frasassi cave ecosystems. Nitrogenase gene expression shows niche differentiation among diazotrophs in symbiotic, biofilm, and sediment microbial communities.
Area of Science:
- Microbiology
- Geochemistry
- Ecology
Background:
- Chemoautotrophy-driven microbial sulfur and carbon cycles are known in deep-sea vents, cold seeps, and sulfidic caves.
- Nitrogen fixation, a crucial process for ecosystem productivity, remains poorly understood in these unique environments.
Purpose of the Study:
- To investigate nitrogen fixation in the Frasassi cave ecosystem, a sulfide-rich, chemoautotrophy-based environment.
- To identify and characterize diazotrophic microbial communities in different niches within the cave waters.
Main Methods:
- Utilized (15)N2 isotope labeling, acetylene reduction assay, and nitrogenase gene (nifH) expression analyses.
- Examined nitrogen fixation in three distinct microbial niches: symbiotic communities of Niphargus amphipods, Beggiatoa-dominated biofilms, and sulfidic sediment.
Main Results:
- Evidence of nitrogen fixation was found across all three investigated niches.
- Nitrogenase gene expression demonstrated niche differentiation of diazotrophic Proteobacteria.
- Specific diazotrophs were identified in symbiotic communities (Thiothrix-related), Beggiatoa biofilms (Beggiatoa- and Desulfovibrio-related), and sulfidic sediment (Geobacter, Azoarcus, Desulfovibrio-related).
Conclusions:
- This study provides the first insights into nitrogen fixation within permanently dark cave ecosystems.
- Diazotrophy is likely widespread in chemosynthetic communities, contributing significantly to nutrient cycling in aphotic environments.
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