Anaerobic growth of halophilic archaeobacteria by reduction of fumarate

A number of strains of halophilic archaeobacteria of the genera Halobacterium and Haloferax were able to grow anaerobically using fumarate as electron acceptor. The species showing the best anaerobic growth with fumarate were Haloferax volcanii and Haloferax denitrificans. The two Haloarcula species tested did not show anaerobic growth enhancement with fumarate. During anaerobic growth of Haloferax volcanii in the presence of fumarate, succinate accumulated in the medium with a stoichiometry of only 0.16-0.23 mmol succinate per mmol fumarate consumed; this can be explained by the use of succinate for assimilatory purposes. The ability to reduce fumarate to succinate did not correlate with the ability to grow anaerobically using nitrate, dimethylsulphoxide or trimethylamine N-oxide as terminal electron acceptors. Anaerobic respiration with fumarate as electron acceptor supplies the halophilic archaeobacteria with an additional mode of energy generation in the absence of molecular oxygen.