溶存酸素濃度および基質のC/N比が脱窒素汚泥内の<i>nirS</i> mRNA転写量に及ぼす影響

Abstract

The transcription level of the nitrite reductase gene of denitrifying bacteria in a lab-scale denitrifying reactor was investigated by real-time reverse transcription (RT)-PCR technique as an indicator of in-situ microbial activity. Two types of batch experiment were conducted to clarify the effects of dissolved oxygen (DO) and carbon/nitrogen (C/N) ratio on the relative nirS mRNA level in denitrifying sludge. The reverse transcription of total RNA with the primer, nirS 6R, specific for the nirS gene was suitable for the subsequent quantification of the nirS gene by real-time PCR. The presence of DO and a low C/N ratio in the medium resulted in a rapid decrease in the relative transcription level of nirS mRNA from 105 to 103 copies·ng-1 total RNA within four hours of the batch experiments. The relative transcription remained at the same level after nitrate concentration decreased to a level low enough to reduce denitrification rate. Although there was no relationship between the denitrification rate of the reactor and the relative transcription level of nirS mRNA in the batch experiments, a quick response of transcriptional induction of nirS mRNA corresponding to the changes in DO and C/N ratio was detected.