T H E formation of pyrite (FeS 2 ), an important factor in determining the global redox balance 1 , has recently attracted biological interest as a possible direct source of energy for early life 2-5 . The theory implies that carbon dioxide fixation, in competition with hydrogen formation, can serve as the electron sink for pyrite formation and it seems to be supported by the detection of minute grains of pyrite and iron sulphides inside bacteria [5][6][7][8] . Yet it clashes with the conventional assumption that elemental sulphur or a sulphur equivalent (polysulphide or thiosulphate) is the mandatory oxidant for pyrite formation 9,10 . It has been stressed that the reaction FeS + H 2 S-FeS 2 + H 2 (with H + as the oxidant) has "never been observed... during several years of experimentation" 10. Here we report the formation of both pyrite and molecular hydrogen under fastidiously anaerobic conditions in the aqueous system of FeS and H 2 S.Of the geochemical environments in which pyrite can form, two are of particular biological significance: sedimentary systems, in which pyrrhotite (Fe^S) is extremely rare 11 and in which pyrite seems to be formed from amorphous FeS 1012 , and hydrothermal systems in which pyrite may be formed not only from amorphous FeS but also from pyrrhotite 11. We have modelled these by reacting aqueous H 2 S at 100 °C for 14 days, under strictly anaerobic and nearly neutral conditions, either with amorphous FeS, precipitated from aqueous FeS0 4 , or with synthetic (metal basis) pyrrhotite. Our experiments show a linkage between pyrite formation (ascertained by X-ray diffraction) and hydrogen evolution (determined by gas chromatography). Typical results are shown in Table 1 All procedures were carried out under C02. The solutions were prepared from doubly distilled water, through which N2-C02 had been bubbled for 2 h. Serum bottles (120 ml) were charged with the suspension of FeS, stoppered and supplied with a N2-C02 atmosphere (80:20,100 kPa) and then charged with an injection of 2 mmol H2S gas and adjusted to pH 6.5 with NaOH. The HaS gas was prepared by adding 50% H2S04 to Na2S • 9H20 in an evacuated serum bottle. During incubation for 14 d at 100 °C in a rotary shaker (100 r.p.m.), the serum bottles were kept in anaerobic cylinders with an N2-C02 atmosphere (80:20, 180 kPa). H2 was determined by gas chromatography (Hewlett Packard 5890). A packed column filled with Molecular Sieve 5A (Supelco) was used (injection temperature, 190 °C; oven temperature, 140 °C; detection temperature, 220 °C; carrier gas, N2). For runs 1, 3 and 4, the averages and the standard deviations of the H2 measurements of three repeats of the reaction are given. Run 2 was not repeated. The traces of Ha in control runs lb, 2b and 4b are barely above the background (detection limit 0.1 n-mol) and may be due to the reaction 2FeS+2H + -» FeS2 +Fe 2+ +H2. In control run 5, the trace of H2 may be due to thermal decomposition (H2S ^ H2+S). The solid phase was dried in an anaerobic chamber (N2:H2=95:5) and the mineral comp...

A novel rod-shaped hyperthermophilic archaeum has been isolated from a boiling marine water hole at Maronti Beach, Ischia, Italy. It grew optimally at 100°C and pH 7.0 by aerobic respiration as well as by dissimilatory nitrate reduction, forming dinitrogen as a final product. Organic and inorganic compounds served as substrates during aerobic and anaerobic respiration. Growth was inhibited by elemental sulfur. The cell wall was composed of a surface layer of hexameric protein complexes arranged on a p6 lattice. The core * Corresponding author.

The type strain (ATCC 23270) and two other strains of Thiobacillus ferrooxidans were able to grow by hydrogen oxidation, a feature not recognized before. When cultivated on H2, a hydrogenase was induced and the strains were less extremely acidophilic than during growth on sulfidic ores. Cells of T. ferrooxidans grown on H2 and on ferrous iron showed 100% DNA homology. Hydrogen oxidation was not observed in eight other species of the genus Thiobacillus and in Leptospirillum ferrooxidans. Members of the eubacterial genus Thiobacillus are presently characterized by their ability to oxidize elemental sulfur and other sulfur compounds (7). T. ferrooxidans is able to grow by oxidation of ferrous iron or sulfidic ores. As a result of these properties, it is the most important bacterium in bioleaching (6). Novel rod-shaped isolates are able to grow by oxidation of galena (PbS). Alternatively, they are oxidizers of molecular hydrogen (E. Drobner, H. Huber, and K. 0. Stetter, unpublished data). In this study, we examined

Abstract. From an uranium mine three strains of rodshaped, mesophilic, chemolithoautotrophic bacteria were isolated. They grow by oxidation of H 2 S, galena (PbS) and H 2 . Anglesite (PbS0 4 ) is formed from galena. No ferrous iron is oxidized by the isolates. They grow between pH 4 and 6.5 at temperatures of about 9 to 41 °C (optimum around 27 °C). The G + C content of the DNA is around 66 mol %. Based on their ability to oxidize sulfur compounds, the new organisms belong to the genus Thiobacillus. No significant homology with Thiobacillus ferrooxidans and Thiobacillus cuprinus was detected by DNA-DNA hybridization. Therefore the new isolates represent a new species within the genus Thiobacillus. Based on the unusual growth on galena, we name the new species Thiobacillus plumbophilus (type strain Gro7; DSM 6690).

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.