Biosynthetic reactions, flux of metabolites and generation of ATP within the archaeal community Nanoarchaeum equitans and Ignicoccus KIN4/I
Zusammenfassung der Projektergebnisse
Nanoarchaeum equitans and Ignicoccus hospitalis represent a unique association of two Archaea. Both form a stable co-culture which is mandatory for N. equitans but not for the host I. hospitalis. In this project, we investigated interactions and mutual influences between these two organisms. The designated “host” I. hospitalis was described as a member of the crenarchaeal order Desulfurococcales. It is an anaerobic, strictly chemolithoautotrophic hyperthermophile growing exclusively by reduction of elemental sulfur using molecular hydrogen as electron donor. I. hospitalis cells exhibit a unique morphology: they lack an S-layer and are the only Archaea which are surrounded by an outer membrane. To our surprise, by the use of labelling experiments, NMR analyses, and enzymatic tests a novel CO2-fixation pathway and further unusual biosynthetic pathways for carbohydrates and amino acids could be elucidated in I. hospitalis. The new CO2- fixation pathway (named dicarboxylate/4-hydroxybutyrate pathway) is based on two carboxylation steps (acetylCoA and PEP). The primary acceptor-molecule acetyl-CoA is regenerated in a similar way as detected recently in Metallosphaera sedula. The “symbiont” N. equitans is the first representative of a novel archaeal phylum, the Nanoarchaeota. However, the exact branching point of this organism within phylogenetic trees depends on the molecule investigated and is an object of ongoing scientific discussion. Several nanoarchaeal 16S rDNA sequences could be obtained from many high temperature biotopes around the world, but no further members of this phylum could be cultivated so far. N. equitans cells are tiny cocci (Ø 350-500 nm; volume about 1% of a normal bacterial cell) growing attached to the surface of I. hospitalis. Various attempts to cultivate N. equitans in the absence of I. hospitalis or on alternative host organisms failed. In fermentation studies final cell concentrations of N. equitans could be significantly increased by expulsion of H2S, the major metabolic end product of I. hospitalis. After separation and purification about one to two grams of N. equitans cells out of 300 liters are obtained. With 490 kb N. equitans has one of the smallest genomes known, lacking nearly all genes for lipid, nucleotide, amino acid or cofactor biosynthesis. In consequence, isolation studies using the optical tweezers revealed that infection with N. equitans inhibited proliferation of individual I. hospitalis cells. However, N. equitans had no influence on doubling times, final cell concentrations, and growth ranges or optima of an I. hospitalis culture. The observed inhibition might be caused by the deprivation of cell components from the host. This was demonstrated by C labelling studies which revealed that N. equitans derives all its membrane lipids from its host. Furthermore, a transfer of amino acids from I. hospitalis to N. equitans could be demonstrated by the use 13C labelled acetate and succinate. At present it can be stated that both organisms exhibit a unique purely archaeal system of two microorganisms which combines characteristics of symbiosis, commensalisms, and parasitism and which we name “intimate association”.
Projektbezogene Publikationen (Auswahl)
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A new phylum of Archaea represented by a nano-sized hyperthermophilic symbiont. Nature 417, 63-67 (2002)
Huber H, Hohn MJ, Rachel R, Fuchs T, Wimmer VC, Stetter KO
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Detection of 16S rDNA sequences representing the novel phylum „Nanoarchaeota”: indication for a wide distribution in high temperature biotopes. System. Appl. Microbiol., 25, 551-554 (2002)
Hohn MJ, Hedlund BP, Huber H
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“Desulfurococcales,” In: M. Dworkin et al., eds., The Prokaryotes: An evolving electronic resource for the microbiological community, 3rd edition, release 3.11, 22th November 2002, Springer-Verlag, New York
Huber H, and Stetter KO
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Heiß, klein und “gemein”: das neue Phylum der “Nanoarchaeota“. Biospektrum 9, 353-355 (2003)
Huber H, Hohn MJ, Jahn U, Rachel R
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The phylum Nanoarchaeota: Present knowledge and future perspectives of a unique form of life. Res. Microbiol. 154, 165-171 (2003)
Huber H, Hohn MJ, Stetter KO, Rachel R
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“Nanoarchaeota” In: M. Dworkin et al., eds., The Prokaryotes: An evolving electronic resource for the microbiological community, 3rd edition, release 3.15, 22th March 2003, Springer-Verlag, New York
Huber H, Hohn MJ, Rachel R, Stetter KO
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Composition of the lipids Nanoarchaeum equitans and their origin from its host Ignicoccus sp. strain KIN4/I. Arch. Microbiol. 182, 404-413 (2004)
Jahn U, Summons R, Sturt H, Grosjean E, Huber H
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A novel kingdom of parasitic Archaea. In: Geothermal Biology and Geochemistry in Yellowstone National Park. Proceeding of the Thermal Biology Institute Workshop, Yellowstone National Park, WY, October 2003 (W.P. Inskeep and T.R. McDermott eds.). Montana State University Publications, Bozeman, MT, USA. pp. 249-259 (2005)
Stetter KO, Hohn MJ, Huber H, Rachel R, Mathur E, Hedlund B, Jahn U
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Ignicoccus hospitalis sp. nov., the host of “Nanoarchaeum equitans”. Int. J. System. Evol. Microbiol. 57, 803-808 (2007)
Paper W, Jahn U, Hohn MJ, Kronner M, Näther DJ, Burghardt T, Rachel R, Stetter KO, Huber H
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Insights into the autotrophic CO2 fixation pathway of the archaeon Ignicoccus hospitalis: comprehensive analysis of the central carbon metabolism. J. Bacteriol. 189, 4108-19 (2007)
Jahn U, Huber H, Eisenreich W, Hügler M, Fuchs G
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Nanoarchaeota. In: Archaea: Evolution, physiology and molecular biology (R Garrett & HP Klenck eds). Blackwell Publishing, Oxford, UK, pp 51-58 (2007)
Huber H, Rachel R
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The dominating outer membrane protein of the hyperthermophilic Archaeum Ignicoccus hospitalis: a novel pore-forming complex. Molec. Microbiol. 63, 168-176 (2007)
Burghardt T, Näther DJ, Junglas B, Huber H, Rachel R
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A dicarboxylate/4-hydroxybutyrate autotrophic carbon assimilation cycle in the hyperthermophilic Archaeum Ignicoccus hospitalis. PNAS 105, 7851-7856 (2008)
Huber H, Gallenberger M, Jahn U, Eylert E, Berg I, Kockelkorn D, Eisenreich W, Fuchs G
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Ignicoccus hospitalis and Nanoarchaeum equitans: Ultrastructure, cell-cell interaction, and 3D reconstruction from serial sections of freeze-substituted cells and by electron cryotomography. Arch Microbiol, 190, 395-408 (2008)
Junglas B, Briegel A, Burghardt T, Walther P, Huber H, Rachel R
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Nanoarchaeum equitans and Ignicoccus hospitalis: new insights into a unique, intimate association of two Archaea. J. Bacteriol. 190, 1731-1737 (2008)
Jahn U, Gallenberger M, Paper W, Junglas B, Stetter KO, Eisenreich W, Rachel R, Huber H
