V. T. Marteinsson CNRS, UPR 9042, Station Biologique, B.P. 74, 29682 Roscoff Cédex, France
J. L. Birrien CNRS, UPR 9042, Station Biologique, B.P. 74, 29682 Roscoff Cédex, France
J. K. Kristjansson Technological Institute of Iceland and University of Iceland, Keldnaholt, 112 Reykjavik, Iceland
D. Prieur CNRS, UPR 9042, Station Biologique, B.P. 74, 29682 Roscoff Cédex, France
The first thermophilic (optimal temperature >60°C) and hyperthermophilic (optimal temperature >80°C) micro-organisms were isolated from continental and shallow water biotopes where the temperature of liquid water does not exceed 100°C under atmospheric pressure. The discovery of deep-sea hydrothermal vents and black smokers with fluids up to 350°C represented a new challenge for microbiologists searching for the upper limit of temperature allowing life. However, the maximum temperature demonstrated for growth of micro-organisms is still 110°C. Two genera can grow up to this temperature: Pyrodictium and Methanopyrus. The first is represented by 3 species (occultum, brockii and abyssi), the last isolated from deep-sea vents. The second is represented by one species, M. kandleri and has been found in shallow waters and deep-sea vents as well. These micro-organisms belong to the Archaeal domain, and are strictly anaerobic.
Because of the steep temperature gradient existing in between the inner pipe of an hydrothermal chimney and the deep ocean water surrounding it, it was almost certain that hot temperatures were associated with reduced i.e. anaerobic niches. Thus, searches for anaerobic hyperthermophiles were encouraged and most of the deep-sea hyperthermophiles isolated and described to date are strictly anaerobic (peptide fermenters, sulphur or sulphate reducers, methanogens).
Stimulating conversations with geologists involved in the study of Mid-Atlantic Ridge (MAR) deep-sea vents revealed to us that some particular mineral structures of this area (beehive-like chimneys) could represent a new kind of biotope for thermophilic life. Because of its porosity, a "beehive" allows some mixing of hot fluid with cold water, so generating niches with temperatures around 70°C that could also be oxygenated.
Hydrothermal vents of the Snake Pit area have been explored by the manned submersible ALVIN (WHOI) during the MAR 93 cruise, co-organized by WHOI and INSU. Samples of hot fluids and pieces of active smokers were collected and colonization modules exposed for several days. These samples were processed aboard the RV Jean Charcot, and further in the laboratory for enrichment of aerobic thermophilic organisms. Twenty-eight non-sporulating aerobes and 45 spore forming bacilli were isolated, described and their phenotypes compared with those of relative type strains by numerical taxonomy.
The non-sporulating isolates consisted of pleomorphic rods, single cells or pairs, formed filaments of variable lengths and grew at 70°C or some up to 80°C. They were halotolerant and unable to grow anaerobically, except for some strains in the presence of nitrate. Rhodothermus (R-10), Thermus aquaticus (YT-1), Thermus scotoductus (X-1) and one yellow pigmented Thermus were included in the numerical taxonomy analysis. Results from unweighted average linkage (UPGMA) clustering applied to a similaritary matrix derived from the simple matching coefficient showed the formation of five main clusters which were defined for at least 80% similarity, and gathered all wild strains except 2. Reference strain X-1 was included in one cluster at a level of 83%, but other reference strains showed less than 55% similarity with the deep-sea isolates.
The spore-forming bacilli were all halotolerant and grew aerobically above 65°C. Numerical taxonomy analysis carried out with 11 high temperature Bacillus reference strains showed 7 main clusters, defined for at least 83% similarity. None of the reference strains was included in a cluster containing wild isolates.
Data available on these 2 kinds of aerobic thermophiles are not enough to assign the strains to a well defined taxonomic position, particularly for the non sporulating isolates. Further biochemical features such as lipid composition, but also genotypic data (G+C%, DNA/DNA hybridization with type strains, 16S rRNA sequences) are required to assign the strains to the already known genera (Thermus or Bacillus), or eventually new taxa. However, this work demonstrated clearly that thermophilic aerobic niches do exist in the deep-sea vent biotopes. Although it is not yet possible to estimate the sizes of these niches, it is certain that they are colonized by aerobic thermophilic microbial communities with a significant specific diversity (several novel species are expected), as shown by the numerical taxonomy data.
Burggraf, S., Stetter, K.O., Rouviere, P. & Woese, C.R., Systematic and Applied Microbiology 14, 346-351 (1991).
Marteinsson, V.T., Birrien, J.L., Kristjansson, J.K. & Prieur, D., FEMS Microbiology Ecology 18, 163-174 (1995).
Marteinsson, V.T., Birrien, J.L., Jeanthon, C. & Prieur, D. (submitted).
Pley, U., Schipka, J., Gambacorta, A., Jannasch, H.W., Fricke, H., Rachel, R. & Stetter, K.O., Systematic and Applied Microbiology 14, 245-253 (1991).
Prieur, D., Erauso, G. & Jeanthon, C., Planet. Space Sci. 43, 115-122 (1995).
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