Karl O. Stetter

Pyrococcus furiosus sp. nov. represents a novel genus of marine heterotrophic archaebacteria growing optimally at 100°C

Ten strains representing a novel genus of marine thermophilic archaebacteria growing at between 70 and 103°C with an optimal growth temperature of 100°C and a doubling time of only 37 min were isolated from geothermally heated marine sediments at the beach of Porto di Levante, Vulcano, Italy. The organisms are spherical-shaped, 0.8 to 2.5 μm in width and exhibit monopolar polytrichous flagellation. They are strictly anaerobic heterotrophs, growing on starch, maltose, peptone and complex organic substrates. Only CO2 and H2 could be detected as metabolic products, the latter being inhibitory to growth at high concentrations. Hydrogen inhibition can be prevented by the addition of So, whereupon H2S is formed in addition, most likely as the result of a “detoxification” reaction. The GC-content of the DNA of isolate Vc 1 is 38 mol%. The new genus is named Pyrococcus, the “fireball”. Type species and strain is Pyrococcus furiosus Vc 1 (DSM 3638).

Thermotoga maritima sp. nov. represents a new genus of unique extremely thermophilic eubacteria growing up to 90°C

A novel type of bacterium has been isolated from various geothermally heated locales on the sea floor. The organisms are strictly anaerobic, rod-shaped, fermentative, extremely thermophilic and grow between 55 and 90°C with an optimum of around 80°C. Cells show a unique sheath-like structure and monotrichous flagellation. By 16S rRNA sequencing they clearly belong to the eubacteria, although no close relationship to any known group could be detected. The majority of their lipids appear to be unique in structure among the eubacteria. Isolate MSB8 is described as Thermotoga maritima, representing the new genus Thermotoga.

A new phylum of Archaea represented by a nanosized hyperthermophilic symbiont

According to small subunit ribosomal RNA (ss rRNA) sequence comparisons all known Archaea belong to the phyla Crenarchaeota, Euryarchaeota, and—indicated only by environmental DNA sequences—to the ‘Korarchaeota’. Here we report the cultivation of a new nanosized hyperthermophilic archaeon from a submarine hot vent. This archaeon cannot be attached to one of these groups and therefore must represent an unknown phylum which we name ‘Nanoarchaeota’ and species, which we name ‘Nanoarchaeum equitans’. Cells of ‘N. equitans’ are spherical, and only about 400 nm in diameter. They grow attached to the surface of a specific archaeal host, a new member of the genus Ignicoccus. The distribution of the ‘Nanoarchaeota’ is so far unknown. Owing to their unusual ss rRNA sequence, members remained undetectable by commonly used ecological studies based on the polymerase chain reaction. ‘N. equitans’ harbours the smallest archaeal genome; it is only 0.5 megabases in size. This organism will provide insight into the evolution of thermophily, of tiny genomes and of interspecies communication.

The Sulfolobus-“Caldariella” group: Taxonomy on the basis of the structure of DNA-dependent RNA polymerases

The similarity of the morphology and of DNA composition, the homology of the component patterns of DNA-dependent RNA polymerases and their immunochemical crossreactivity support the conclusion that several extreme thermoacidophiles are related to each other. We name two new species of the genus Sulfolobus. The first, Sulfolobus solfataricus (DSM 1616 and DSM 1617) has the same GC content in its DNA and the same general properties as S. acidocaldarius, but differs significantly from the latter species in the molecular weights of the 11 components of its RNA polymerase and in the salt requirements of this enzyme. The second, Sulfolobus brierleyi, DSM 1651, differs from S. acidocaldarius in several respects. The cells show much less stability at neutral pH. The GC content is significantly lower. The RNA polymerase lacks two components present in the enzymes from the other species. The residual 9 components show larger size differences from the homologous subunits of the S. acidocaldarius enzyme.Like the enzyme from S. solfataricus, the polymerase from S. brierleyi yields an incomplete immunochemical crossreaction with an antibody against the RNA polymerase from S. acidocaldarius.The isolates DSM 1616 and DSM 1617 of Sulfolobus solfataricus are probably identical with or similar to the “Caldariella” strains MT 3 and MT 4, isolated by de Rosa et al. (1975).Like all other known archaebacterial RNA polymerases the enzymes from these species are insensitive to rifampicin and streptolydigin.

Aquifex pyrophilus gen.nov. sp. nov., represents a novel group of marine hyperthermophilic hydrogen-oxidizing bacteria

Summary From hot marine sediments (depth: 106 m) at the Kolbeinsey Ridge, Iceland, novel bacterial hyperthermophiles were isolated. Cells were Gram-negative highly motile rods exhibiting a complex envelope consisting of murein, an outer membrane and a surface protein layer. Growth occurred between 67 and 95 °C (opt.: 85 °C; 75 min doubling time), pH 5.4 and 7.5 (opt.: pH 6.8), and 1 to 5% NaCl (opt.: 3% NaCl). The novel isolates were strict chemolithoautotrophs. They used molecular hydrogen, thiosulfate and elemental sulfur as electron donors and oxygen (low concentrations) and nitrate as electron acceptors. During growth, sulfuric acid was formed from S° and thiosulfate. In the late logarithmic growth phase, H2S was formed from S° and H2. The core lipids consisted mainly of alkyl ethers of glycerol. The GC content of the DNA was 40 mol%. By 16S rRNA comparisons, the new isolates did not belong to any of the phyla known and represent the deepest phylogenetic branch-off within the Bacteria domain. Based on the physiological and molecular properties of the new isolates, we describe here a new genus, which we name Aquifex (the “water-maker”). The type species is Aquifex pyrophilus (type strain: Kol5a; DSM 6858).

Pyrodictium gen. nov., a New Genus of Submarine Disc-Shaped Sulphur Reducing Archaebacteria Growing Optimally at 105°C.

Six isolates of a new genus of anaerobic archaebacteria, named Pyrodictium, were isolated from a submarine solfataric field off Vulcano, Italy. These disc-shaped organisms grew at at least 110°C with an optimum around 105°C, and formed highly unusual networks of fibres. They were hydrogen-sulphur-autotrops. During growth in a fermenter, pyrite was formed. Two species can be distinguished: Pyrodictium occultum - which has a G + C-content of 62 mol%, and, as the dominant component in its cell envelope, a glycoprotein with a molecular weight of 172000 - and Pyrodictium brockii - which has a G + C-content of 51.5 to 56.6 mol%, a protein of molecular weight 150000 as its major cell envelope component, and whose growth yield is greatly increased in the presence of yeast extract.

Extremophiles and their adaptation to hot environments

Water‐containing terrestrial, subterranean and submarine high temperature areas harbor a variety of hyperthermophilic bacteria and archaea which are able to grow optimally above 80°C. Hyperthermophiles are adapted to hot environments by their physiological and nutritional requirements. As a consequence, cell components like proteins, nucleic acids and membranes have to be stable and even function best at temperatures around 100°C. The chemolithoautotrophic archaeon Pyrolobus fumarii is able to grow at 113°C and, therefore, represents the upper temperature border of life. For the first time, (vegetative) cultures of Pyrolobus and Pyrodictium are able to survive autoclaving.

Isolation of Extremely Thermophilic Sulfate Reducers: Evidence for a Novel Branch of Archaebacteria

Extremely thermophilic archaebacteria are known to be metabolizers of elemental sulfur and the methanogens. A novel group of extremely thermophilic archaebacteria is described, which consists of sulfate-respiring organisms that contain pure factor 420 and that have been isolated from marine hydrothermal systems in Italy. They possess a third type of archaebacterial RNA polymerase structure previously unknown, indicating an exceptional phylogenetic position. Most likely, this group represents a third major branch within the archaebacteria. The existence of sulfate reducers at extremely high temperatures could explain hydrogen sulfide formation in hot sulfate-containing environments, such as submarine hydrothermal systems and deep oil wells.

The complete genome of hyperthermophile Methanopyrus kandleri AV19 and monophyly of archaeal methanogens

We have determined the complete 1,694,969-nt sequence of the GC-rich genome of Methanopyrus kandleri by using a whole direct genome sequencing approach. This approach is based on unlinking of genomic DNA with the ThermoFidelase version of M. kandleri topoisomerase V and cycle sequencing directed by 2′-modified oligonucleotides (Fimers). Sequencing redundancy (3.3×) was sufficient to assemble the genome with less than one error per 40 kb. Using a combination of sequence database searches and coding potential prediction, 1,692 protein-coding genes and 39 genes for structural RNAs were identified. M. kandleri proteins show an unusually high content of negatively charged amino acids, which might be an adaptation to the high intracellular salinity. Previous phylogenetic analysis of 16S RNA suggested that M. kandleri belonged to a very deep branch, close to the root of the archaeal tree. However, genome comparisons indicate that, in both trees constructed using concatenated alignments of ribosomal proteins and trees based on gene content, M. kandleri consistently groups with other archaeal methanogens. M. kandleri shares the set of genes implicated in methanogenesis and, in part, its operon organization with Methanococcus jannaschii and Methanothermobacter thermoautotrophicum. These findings indicate that archaeal methanogens are monophyletic. A distinctive feature of M. kandleri is the paucity of proteins involved in signaling and regulation of gene expression. Also, M. kandleri appears to have fewer genes acquired via lateral transfer than other archaea. These features might reflect the extreme habitat of this organism.

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).