ammonifex ammonifex ammonifex is a gram-negative, extremely thermophilic, strictly anaerobic and motile genus of bacteria from the family of thermoanaerobacteraceae. ammonifex scientific classification domain: bacteria phylum: bacillota order: thermoanaerobacterales family: thermoanaerobacteraceae genus: ammonifexhuber and stetter 1996 type species ammonifex degensii species a. degensii a. thiophilus