Aims: To quantitatively analyse the changes to amoA mRNA (ammonia mono-oxygenase encoding mRNA) profiles in response to a change in ammonia oxidation activity in a complex microbial community. Methods and Results: The amoA mRNA levels in both a batch-mode incubation and a continuously fed nitrification reactor were determined by real-time reverse transcription-PCR analysis. The amoA mRNA level changed rapidly in response to the change in environmental conditions which affect ammonia oxidation activity. Conclusion: An increase in amoA mRNA level can be detected within 1-2 h in response to an initiation of cell activity whereas a decrease in amoA mRNA level is detected within 24 h in response to a cessation of activity. Significance and Impact of the Study: amoA mRNA, which shows sensitive response to ammonia oxidation activity, can be used as a biomarker of ammonia oxidation activity in wastewater treatment processes where many bacterial species exist.
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