Thermosipho africanus gen. nov., a Member of the "Thermotogales"

No abstract

SummaryFive new isolates of archaeal coccoid thermoacidophiles were obtained from Icelandic solfataric fields. They are strict chemolithoautotrophs gaining energy by oxidation of S° and sulfidic ores. The new strains grow between 50 and 75 °C and pH 1 and 4.5 and tolerate NaCl concentrations of up to 3.0%. The GCcontent of their DNA is 38 mol%.The new isolates resemble members of Sulfolobus in their morphology, their ability to oxidize reduced sulfur compounds and their GC-content. They are different in their strictly chemolithoautotrophic mode of life, their ore-leaching capacity, DNA/DNA hybridization and incomplete serological cross-reaction of RNA polymerase. Therefore, we describe here a new species, Sulfolobus metallicus. Type strain is Sulfolobus metallicus (Kra 23; DSM 6482).

Abstract. Hot springs and hydrothermal systems occurring within volcanic areas are inhabited by hyperthermophilic microorganisms, some of which grow at temperatures up to 110 °C. Hyperthermophiles grow anaerobically or aerobically by diverse metabolic types. Within the high temperature ecocystems, primary production is independent from solar energy.

SummaryMembers of the genera Sulfolobus, Acidianus and Metallosphaera were found to be able to grow chemolithoautotrophically on H2/02. Under these conditions, the strains grew between about 0.2 and 10% 02 per vol. (opt: -1% 02). The oxidation of H2 by 02 was confirmed by the addition of D2 as a tracer. To our knowledge, this is the first demonstration of H2 oxidation by 02 among the Archaea. , 1986). In this respect they resemble members of the genus Thiobacillus. In order to identify possibly existing archaeal H2-oxidizers we examined different members of the Sulfolobales for this metabolic property (Table 1). Type strains and new isolates within the genera Acidianus, Metallosphaera and Sulfolobus were precultured on suitable substrates (Table 1) under shaking (100 rev/min) in 100 ml Erlenmeyer flasks containing 30 ml of Allen's medium, adjusted to pH 2.5 [Allen, 1959). /ml). Sulfolobus metallicus failed to grow under these conditions. Attempts to adapt cells by subcultivation on H2 and air in the presence of decreasing amounts of S° were unsuccessful. With the exception of Sulfolobus metallicus, all strains were successfully transferred more than 10 times in sequence into fresh mineral medium with H2/C02/02 as gas phase always yielding approximately the same final cell concentrations (not shown). This indicated that the cultures were able to grow on H2/02 as energy source. During growth, H2 was determined by gas chromatography (Hewlett-Packard 5890). Consumption of H2 correlated with growth, as shown for Metallosphaera sedula DSM 5348 (Fig. 1) Allen's medium, in the absence of 02, all strains failed to grow (not shown). In order to prove the new metabolic property of the organisms, H2 in the gas phase was replaced by D2 (99.9% pure; Linde, Höllriegelskreuth, Germany). After 4 days incubation, the cultures were centrifuged and the concentration of HDO in the supernatants were determined by NMR spectroscopy (reference: D20). The results are shown in Table 2. Significant amounts of HDO had been formed (for example: 200 |imol/ml HDO in the case of Metallosphaera sedula; cell concentration 2 x 10 8 cells/ml), indicating that the organisms were H2 oxidizers. The strains grew in the presence of 02 concentrations from about 0.2% to 10% Ö2 with an optimum around 0.5% (not shown). Therefore, they can be considered as microaerophilic. Since members of the deepest bacterial phylogenetic branch (Aquifex pyrophilus) exhibit the same type of metabolism, hydrogenoxidation may be a rather ancient property of microbial life on Earth. Key words: Hydrogen oxidation -Acknowledgements. We wish to thank E. Lang for NMR spectroscopy, L. Schwarzfischer-Pfeilschifter for technical assistance and Dennis Grogan and Patricia Hartzell for critically reading the manuscript. This work was supported by grants of the Bundesministerium für Forschung und Technologie (BMFT, Projektleitung Rohstofforschung, FKZ 03R085A) and the Fonds der Chemischen Industrie.