INDUCTION OF AMMONIA MONOOXYGENASE AND HYDROXYLAMINE OXIDOREDUCTASE MESSENGER-RNAS BY AMMONIUM IN NITROSOMONAS-EUROPAEA

In Nitrosomonas eoropaea, ammonia monooxygenase (AMO) and hydroxylamin e oxidoreductase (HAO) catalyse the oxidation of ammonia (NH3) to nitr ite (NO2-). A transcript of 3500 bases hybridizes to probes for amoA a nd amoB (genes that code for AMO proteins). A transcript of 2100 bases hybridizes to probes for hao (the gene that codes for HAO). Induction of the mRNAs detected by amo and hao probes required the presence of ammonium (NH4+). To correlate new levels of mRNA with de novo activity , existent mRNA pools and AMO activity were depleted prior to inductio n by NH4+. The mRNAs of AMO and HAO were depleted by depriving the cel ls of energy for at least 8h; AMO activity was inactivated with acetyl ene (C2H2) after mRNA depletion. In cells treated this way, levels of new AMO mRNA and de novo AMO enzyme activity were correlated with incr eased NH4+ concentrations up to 1 mM after 3 h of incubation. HAO mRNA also increased in the NH4+-treated cells. Other proteins and RNAs ind uced by NH4+ were detected in (CO2)-C-14-labelling experiments. The AM O and HAO mRNAs were preferentially synthesized during energy-limiting conditions.