EFFECT OF TUNGSTATE ON NITRATE REDUCTION BY THE HYPERTHERMOPHILIC ARCHAEON PYROBACULUM-AEROPHILUM

Pyrobaculum aerophilum, a hyperthermophilic archaeon, can respire eith er with low amounts of oxygen or anaerobically with nitrate as the ele ctron acceptor. Under anaerobic growth conditions, nitrate is reduced via the denitrification pathway to molecular nitrogen, This study demo nstrates that P. aerophilum requires the metal oxyanion WO42- for its anaerobic growth on yeast extract, peptone, and nitrate as carbon and energy sources. The addition of 1 mu M MoO42- did not replace WO42- fo r the growth of P. aerophilum. However, cell growth was completely inh ibited by the addition of 100 mu M MoO42- to the culture medium. At lo wer tungstate concentrations (0.3 mu M and less), nitrite was accumula ted in the culture medium. The accumulation of nitrite was abolished a t higher WO42- concentrations (<0.7 mu M). High-temperature enzyme ass ays for the nitrate, nitrite, and nitric oxide reductases were perform ed, The majority of all three denitrification pathway enzyme activitie s was localized to the cytoplasmic membrane, suggesting their involvem ent in the energy metabolism of the cell. While nitrite and nitric oxi de specific activities were relatively constant at different tungstate concentrations, the activity of nitrate reductase was decreased fourf old at WO42- levels of 0.7 mu M or higher. The high specific activity of the nitrate reductase enzyme observed at low WO42- levels (0.3 mu M or less) coincided with the accumulation of nitrite in the culture me dium. This study documents the first example of the effect of tungstat e on the denitrification process of an extremely thermophilic archaeon . We demonstrate here that nitrate reductase synthesis in P. aerophilu m occurs in the presence of high concentrations of tungstate.