Abstract
The transcription level of amoA mRNA encoding a subunit of ammonia monooxygenase (amo) in ammonia-oxidizing bacteria (AOB) was quantified by competitive reverse transcription (RT)-PCR methods. The effects of ammonia concentration and dissolved oxygen (DO) on the transcription levels of amoA mRNA and 16S rRNA in AOB were evaluated to conduct batch experiments with nitrifying biofilms taken from a lab-scale reactor treating artificial wastewater. A batch incubation without ammonia resulted in the rapid decrease in the transcription level of amoA mRNA from 2.2 X 105 copies·ng-1-total RNA to 2.3 X 104 copies·ng-1 within four hours, while the 16S rRNA transcription level in AOB reduced to almost 50% of the level at the start of incubation. At a subsequent incubation with ammonia for eight hours a slight increase in the transcription level of amoA mRNA occurred, whereas the 16S rRNA transcription level recovered to 80% of the level at the start of incubation. The copy numbers of amoA mRNA and 16S rRNA showed almost fixed values for over eight hours in the absence of dissolved oxygen. RT-PCR will provide a basis for the development of new monitoring technologies and operational strategies for ammonia removal processes.
