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Autotrophic CO2 fixation pathways in archaea (Crenarchaeota)
Michael Hügler1, Harald Huber, Karl Otto Stetter
1Mikrobiologie, Institut für Biologie II, Universität Freiburg, Schänzlestrasse 1, Germany.
Archives of Microbiology
|March 1, 2003
Summary
Crenarchaeota utilize diverse autotrophic pathways for carbon dioxide fixation, including the reductive citric acid cycle, 3-hydroxypropionate cycle, and potentially the Calvin cycle. These pathways vary across different Crenarchaeota taxa.
Area of Science:
- Microbiology
- Biochemistry
- Archaea
Background:
- Autotrophic pathways are crucial for carbon fixation in many microorganisms.
- Crenarchaeota are a domain of archaea known for their diverse metabolic capabilities.
- Understanding CO2 fixation pathways in archaea provides insights into early life and microbial ecology.
Purpose of the Study:
- To investigate the autotrophic carbon dioxide fixation pathways in various thermophilic Crenarchaeota species.
- To identify key enzymes associated with known CO2 fixation routes within different Crenarchaeota families.
- To elucidate the diversity and distribution of these metabolic pathways across Crenarchaeota taxa.
Main Methods:
- Enzyme activity assays were performed on representative Crenarchaeota species.
- Key enzymes of the reductive citric acid cycle, Calvin cycle, and 3-hydroxypropionate cycle were targeted.
- Comparative analysis of enzyme profiles across different families (Thermoproteaceae, Pyrodictiaceae, Desulfurococcaceae, Sulfolobaceae).
Main Results:
- Pyrobaculum islandicum utilizes the reductive citric acid cycle.
- Pyrodictium abyssi and Pyrodictium occultum possess ribulose 1,5-bisphosphate carboxylase but lack phosphoribulokinase, indicating potential Calvin cycle limitations.
- Ignicoccus islandicus and Ignicoccus pacificus show pyruvate oxidoreductase but lack key enzymes for known pathways.
- Metallosphaera sedula, Acidianus ambivalens, and Sulfolobus sp. strain VE6 employ the 3-hydroxypropionate cycle, with enzymes upregulated during autotrophic growth.
- A modified acetyl-CoA regeneration pathway may exist in Metallosphaera sedula.
Conclusions:
- Crenarchaeota exhibit a mosaic of at least three distinct autotrophic CO2 fixation pathways.
- The distribution of these pathways correlates with 16S rRNA-based taxonomic classification.
- Further research is needed to confirm the Calvin cycle in Pyrodictium and the exact CO2 fixation mechanism in Ignicoccus.