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 neu tral volcanic hot spring. The gram-negative, rod-shaped cells were mot ile 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 occu rred 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 accepters and H2S was formed as final pr oduct. Pyruvate was fermented to acetate, CO2 and hydrogen. The GC-con tent of the DNA was 54 mol%. On the basis of its 16S rRNA sequence, th e neu isolate represents a new genus, belonging to the ''low G+C'' sub group of the gram-positive bacteria. Strain KC4 (DSM 10501) is describ ed as the type strain of a new genus and species, which we name Ammoni fex degensii.