title: Autotrophic CO2 fixation pathways in archaea (Crenarchaeota).
abstract: Representative autotrophic and thermophilic archaeal species of different families of Crenarchaeota were examined for key enzymes of the known autotrophic CO(2) fixation pathways. Pyrobaculum islandicum ( Thermoproteaceae) contained key enzymes of the reductive citric acid cycle. This finding is consistent with the operation of this pathway in the related Thermoproteus neutrophilus. Pyrodictium abyssi and Pyrodictium occultum ( Pyrodictiaceae) contained ribulose 1,5-bisphosphate carboxylase, which was active in boiling water. Yet, phosphoribulokinase activity was not detectable. Operation of the Calvin cycle remains to be demonstrated. Ignicoccus islandicus and Ignicoccus pacificus ( Desulfurococcaceae) contained pyruvate oxidoreductase as potential carboxylating enzyme, but apparently lacked key enzymes of known pathways; their mode of autotrophic CO(2) fixation is at issue. Metallosphaera sedula, Acidianus ambivalens and Sulfolobus sp. strain VE6 ( Sulfolobaceae) contained key enzymes of a 3-hydroxypropionate cycle. This finding is in line with the demonstration of acetyl-coenzyme A (CoA) and propionyl-CoA carboxylase activities in the related Acidianus brierleyi and Sulfolobus metallicus. Enzymes of central carbon metabolism in Metallosphaera sedula were studied in more detail. Enzyme activities of the 3-hydroxypropionate cycle were strongly up-regulated during autotrophic growth, supporting their role in CO(2) fixation. However, formation of acetyl-CoA from succinyl-CoA could not be demonstrated, suggesting a modified pathway of acetyl-CoA regeneration. We conclude that Crenarchaeota exhibit a mosaic of three or possibly four autotrophic pathways. The distribution of the pathways so far correlates with the 16S-rRNA-based taxa of the Crenarchaeota.
authors.affiliation: Mikrobiologie, Institut für Biologie II, Universität Freiburg, Schänzlestrasse 1, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Hügler
authors.forename: Harald
authors.initials: H
authors.lastname: Huber
authors.forename: Karl Otto
authors.initials: KO
authors.lastname: Stetter
authors.forename: Georg
authors.initials: G
authors.lastname: Fuchs
mesh_terms: D002245:Carbon Dioxide / Q000378:metabolism*; D002952:Citric Acid Cycle; D019615:Crenarchaeota / Q000145:classification / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D008954:Models, Biological; D010802:Phylogeny
chemical_list: D002245:Carbon Dioxide