Formation of ammonium from nitrate during chemolithoautotrophic growth of the extremely thermophilic bacterium ammonifex degensii gen. nov. sp. nov.

A novel, extremely thermophilic bacterium has been isolated from a neutral volcanic hot spring. The gram-negative, rod-shaped cells were motile and exhibited a complex cell wall composed of murein and a surface protein layer covered by a surface coat. The core lipids consisted of non-phytanyl mono- and diethers and of fatty acid esters. Growth occurred between 57 and 77 degrees C (opt.: 70 degrees C), pH 5.0 and 8.0 (opt.: 7.5) and 0 to 1.5% NaCl (opt.: 0.1% NaCl). The new isolate was a strict anaerobe, growing autotrophically by oxidation of hydrogen or formate, reducing nitrate to ammonium. Instead of nitrate, sulfate or sulfur were used as electron acceptors and H2S was formed as final product. Pyruvate was fermented to acetate, CO2, and hydrogen. The GC-content of the DNA was 54 mol%. On the basis of its 16S rRNA sequence, the new isolate represents a new genus, belonging to the "low G+C" subgroup of the gram-positive bacteria. Strain KC4 (DSM 10501) is described as the type strain of a new genus and species, which we name Ammonifex degensii.