Thermoproteales: A novel type of extremely thermoacidophilic anaerobic archaebacteria isolated from Icelandic solfataras

Two types of anaerobic extremely thermoacidophilic bacteria have been isolated from more than 50% of the samples collected in solfataric fields throughout Iceland.

They both possess highly stable cell envelopes with a characteristic subunit structure, are usually rods of variable length (about 1 to more than 50 μ) without septa, but can give rise to spheric bodies which exist either attached to the rods or in free state. Under certain conditions, truly branched filaments are frequently observed. The similarities in morphology and growth characteristics indicate that the two types are related to each other. In view of its variable appearance the larger organism (diameter about 0.4 μm) was called Thermoproteus tenax.

Thermoproteus tenax forms H₂S and CO₂ from elemental sulfur and organic substrates, like glucose, ethanol, malate or formamide.

The absence of murein, the presence of polyisoprenoid ether lipids, the complete resistance against the antibiotics rifampicin, streptomycin, vancomycin and chloramphenicol and the component pattern and rifampicin insensitivity of the DNA-dependent RNA polymerase are evidence that Thermoproteus tenax belongs to the archaebacteria. It represents a novel order of the thermoacidophilic branch of this urkingdom.