Hyperthermophilic Methanogen Research Articles

Methanopyrus kandleri, gen. and sp. nov. represents a novel group of hyperthermophilic methanogens, growing at 110�C

A novel group of hyperthermophilic rod-shaped motile methanogens was isolated from a hydrothermally heated deep sea sediment (Guaymas Basin, Gulf of California) and from a shallow marine hydrothermal system (Kolbeinsey ridge, Iceland). The grew between 84 and 110°C (opt: 98°C) and from 0.2% to 4% NaCl (opt. 2%) and pH 5.5 to 7 (opt: 6.5). The isolates were obligate chemolithoautotrophes using H2/CO2 as energy and carbon sources. In the presence of sulfur, H2S was formed and cells tended to lyse. The cell wall consisted of a new type of pseudomurein containing ornithin in addition to lysine and no N-acetylglucosamine. The pseudomurein layer was covered by a detergent-sensitive protein surface layer. The core lipid consisted exclusively of phytanyl diether. The GC content of the DNA was 60 mol%. By 16S rRNA comparisons the new organisms were not related to any of the three methanogenic lineages. Based on the physiological and molecular properties of the new isolates, we describe here a new genus, which we name Methanopyrus (the “methane fire”). The type species is Methanopyrus kandleri (type strain: AV19; DSM 6324).

Analysis and nucleotide sequence of the genes encoding the surface‐layer glycoproteins of the hyperthermophilic methanogens Methanothermus fervidus and Methanothermus sociabilis

The genes (slgA) encoding the surface-layer glycoproteins of the hyperthermophilic methanogens Methano-thermus pervidus and Methanothermus sociabilis were cloned and sequenced. The nucleotide sequences of these genes differ at only nine positions, resulting in three amino acid differences. In both organisms, the transcription start site was localized by primer extension analyses. The DNA sequence at this site conforms to the promotor box B motif for promotors of archaea. 24 nucleotides upstream of the transcription start is an A + T-rich region, which closely resembles the consensus box A motif of promoters of methanogens. Ribosome binding sites are exactly complementary to the 3' end of the 16S rRNA of these methanogens. Both slgA genes encode for a precursor of the mature surface-layer protein containing 593 amino acid residues with a putative N-terminal signal sequence of 22 amino acid residues. The deduced protein sequences contain 20 sequon structures representing possible carbohydrate-binding sites. In comparison with other surface-layer proteins, these obtained from the two hyperthermophilic methanogens contain unusually high amounts of isoleucine, asparagine and cysteine residues. Predicted secondary structures have a high content of beta-sheet structure (44%) and only 7% alpha-helix structures.

A novel group of abyssal methanogenic archaebacteria (Methanopyrus) growing at 110 °C

THE organisms with the highest growth temperature known so far are members of the archaebacterial genus Pyrodictium1'2. These anaerobic sulphur reducers thrive at temperatures of up to 110 °C within a shallow hydrothermal system off Vulcano, Italy. Only a few hyperthermophilic methanogens are known—members of the genus Methanothermus, which grow exclusively within terrestrial fields of fumaroles from which sulphurous gas is emitted and show an upper growth temperature of 97 °C (ref. 3), and some members of the genus Methanococcus, which grow within deep-sea hydro-thermal systems at temperatures up to about 90 °C (ref. 4). We have now isolated a novel group of methanogenic archaebacteria growing at least at 110°C from sediment samples taken by the research submersible Alvin at the Guaymas Basin hot vents (Gulf of California). This finding demonstrates the unexpected biogenic methanogenesis at temperatures above 100 °C, and, in view of biogeochemistry, could explain isotope discrimination at temperatures that were thought to be unfavourable for biological methanogenesis.