A Microbial Biorealm page on the genus Methanothermobacter thermautotrophicus
Higher order taxa
Cellular organisms; Archaea; Euryarchaeota; Methanobacteria;Methanobacteriales; Methanobacteriaceae; Methanothermobacter
Description and significance
Methanothermobacter thermautotrophicus is a methanogenic Gram-positive microorganism with a cell wall consisting of pseudomurein. This organism is a strictly anaerobic, nonmotile, methane producting archeon. Growth occurs at a pH of 7.2-7.6. This organism is found in thermophilic, anaerobic sewage sludge digestors. Energy metabolism is by the reduction of carbon dioxide to methane. This strain was isolated from sewage sludge in 1971 in Urbana, Illinois.
So far only two prophage pseudomurein autolysins, PeiW and PeiP, have been reported. PeiW and PeiP contain two different N-terminal pseudomurein cell wall binding domains. This finding was used to identify a novel domain, PB007923, on the M. thermautotrophicus genome present in 10 predicted open reading frames. Three homologues were identified in the Methanosphaera stadtmanae genome. Binding studies of fusion constructs of three separate PB007923 domains to green fluorescent protein revealed that it also constituted a cell wall binding domain. Both prophage domains and the PB007923 domain bound to the cell walls of Methanothermobacter species and fluorescence microscopy showed a preference for the septal region. Domain specificities were revealed by binding studies with other pseudomurein-containing archaea. Localized binding was observed for M. stadtmanae and Methanobrevibacter species, while others stained evenly. The identification of the first pseudomurein cell wall binding domains reveals the dynamics of the pseudomurein cell wall and provides marker proteins to study the extracellular pseudomurein biology of M. thermautotrophicus and of other pseudomurein-containing archaea.
Methanothermobacter thermautotrophicus consist of 1 chromosome and is linear.
Describe the size and content of the genome. How many chromosomes? Circular or linear? Other interesting features? What is known about its sequence? Does it have any plasmids? Are they important to the organism's lifestyle?
Cell structure and metabolism
The MCM complex from the archaeon Methanother-mobacter thermautotrophicus is a model for the eukaryotic MCM2-7 helicase. Electron-microscopy single-particle reconstructions of a DNA treated M.thermautotrophicus MCM sample and a ADP.AlF(x) treated sample, respectively assembling as double hexamers and double heptamers. The electron-density maps display an unexpected asymmetry between the two rings, suggesting that large conformational changes can occur within the complex. The structure of the MCM N-terminal domain, as well as the AAA+ and the C-terminal HTH dom-ains of ZraR can be fitted into the reconstructions. Distinct configurations can be modelled for the AAA+ and the HTH domains, suggesting the nature of the conformational change within the complex. The pre-sensor 1 and the helix 2 insertions, important for the activity, can be located pointing towards the centre of the channel in the presence of DNA. We propose a mechanistic model for the helicase activity, based on a ligand-controlled rotation of the AAA+ subunits. Describe any interesting features and/or cell structures; how it gains energy; what important molecules it produces.
Describe any interactions with other organisms (included eukaryotes), contributions to the environment, effect on environment, etc.
How does this organism cause disease? Human, animal, plant hosts? Virulence factors, as well as patient symptoms.
Application to Biotechnology
Does this organism produce any useful compounds or enzymes? What are they and how are they used?
1. In vitro Biosynthesis of Ether-type Glycolipids in the Methanoarchaeon Methanothermobacter thermautotrophicus.
The biosynthesis of archaeal ether-type glycolipids was investigated in vitro using Methanothermobacter thermautotrophicus cell-free homogenates. The sole sugar moiety of glycolipids and phosphoglycolipids of the organism is the beta-D-glucosyl-(1->6)-D-glucosyl (gentiobiosyl) unit. The enzyme activities of archaeol:UDP-glucose beta-glucosyltransferase (monoglucosylarchaeol synthase, MGA synthase) and monoglucosylarchaeol:UDP-glucose beta-1,6-glucosyltransferase (diglucosylarchaeol synthase, DGA synthase) were found in the methanoarchaeon. The synthesis of DGA is probably a two-step glucosylation: (i) archaeol + UDP-glucose -> MGA + UDP; and (ii) MGA + UDP-glucose -> DGA + UDP. Both enzymes required the addition of K(+) ions and archaetidylinositol for their activities. Ten mM MgCl2 stimulated DGA synthase, in contrast to MGA synthase, which did not require Mg(2+). It was likely that the activities of MGA synthesis and DGA synthesis were carried out by different proteins because of the Mg(2+) requirement and their cellular localization. MGA synthase and DGA synthase can be distinguished in cell extracts greatly enriched for each activity by demonstrating differing Mg(2+) requirements of each enzyme. MGA synthase preferred a lipid-substrate with the sn-2,3 stereostructure of the glycerol backbone on which two saturated isoprenoid chains are bound at the sn-2 and sn-3 positions. A lipid-substrate with unsaturated isoprenoid chains or sn-1,2-dialkylglycerol configuration exhibited low activity. Tetraether type caldarchaetidylinositol was also actively glucosylated by the homogenates to form monoglucosyl caldarchaetidylinositol and small amount of diglucosyl caldarchaetidylinositol. The addition of Mg(2+) increased the formation of diglucosyl caldarchaetidylinositol. This suggested that the same enzyme set synthesized the sole sugar moiety of diether type glycolipids and tetraether type phosphoglycolipids.
2. Spontaneous Mutants in trpY and Mutational Analysis of the TrpY Archaeal Transcription Regulator.
Over 90% of Methanothermobacter thermautotrophicus mutants isolated as spontaneously resistant to 5-methyl tryptophan (5MT) had mutations in trpY. Most were single base pair substitutions that identified separate DNA- and tryptophan-binding regions in TrpY. In vivo and in vitro studies revealed that DNA binding was sufficient for TrpY repression of trpY transcription but that TrpY must bind DNA and tryptophan to assemble a complex that represses trpEGCFBAD.
3. Isolation and characterization of an amiloride-resistant mutant of Methanothermobacter thermautotrophicus possessing a defective Na+/H+ antiport.
A spontaneous mutant of Methanothermobacter thermautotrophicus resistant to the Na+/H+ antiporter inhibitor amiloride was isolated. The Na+/H+ exchanger activity in the mutant cells was remarkably decreased in comparison with wild-type cells. Methanogenesis rates in the mutant strain were higher than wild-type cells and resistant to the inhibitory effect of 2 mM amiloride. In contrast, methanogenesis in wild-type cells was completely inhibited by the same amiloride concentration. ATP synthesis driven by methanogenic electron transport or by an electrogenic potassium efflux in the presence of sodium ions was significantly enhanced in the mutant cells. ATP synthesis driven by potassium diffusion potential was profoundly inhibited in wild-type cells by the presence of uncoupler 3,3',4',5- tetrachlorosalicylanilide and sodium ions, whereas c. 50% inhibition was observed in the mutant cells under the same conditions.
(2) Nucleic Acids Res. 2006;34(20):5829-38. Epub 2006 Oct 24. Costa A, Pape T, van Heel M, Brick P, Patwardhan A, Onesti S. Structural basis of the Methanothermobacter thermautotrophicus MCM helicase activity PubMed
(3)Mol Microbiol. 2006 Dec;62(6):1618-30 Steenbakkers PJ, Geerts WJ, Ayman-Oz NA, Keltjens JT Department of Microbiology, Radboud University Nijmegen, Toernooiveld 1, 6525 ED Nijmegen, the Netherlands PubMed
Edited by Anthony Kim, student of Rachel Larsen and Kit Pogliano