Reserchs to control bacterial functions by “signal molecules” have been progressed so far. Signal molecules are small bioactive compounds by which bacteria communicate with each other. This phenomenon is called “Quorum sensing”. In our lab, we applyed these signal molecules to the wastewater treatement plant (WWTP) to activate the nitrification which is a rate-limiting step of N removal. By addition of some kinds of signal molecules to activated sludge which is consisted of a lot of kinds of bacteria, we confirmed that nitrification was activated. However the activation mechanism has not been elucidated. So in this study we tried to solve this mechanism.

　In this study, we evaluated the effect of signal molecules using recombinant nitrosomonas europaea. N.europaea is one of the major bacterias which are involeved in nitrification.This recombinant N.europaea is reporter assay system using the promoter of Hydroxylamine oxidoreductase (HAO). HAO is the one of the main enzymes in nitrification. So luminescence intensity and gene expression of HAO are closely related, this strain is usuful to assess the change of important gene expression which is difficult to see in a wild strain. We conducted the experiment that we added the many kinds of signal moleceles to this recombinant N.europaea and incubate to measure luminescence intensity and nitrification activity afterward. The systems which is added specific signal molecules, their luminescence intensities significantly increased and their nitrification activities also increased in specific condition. To our knowledge, there is no report that N.europaea senses the signal molecules and change their nitrification activites, so this results have novelty. From these results, now we build up a hypothesis that N.europaea senses signal molecules directly to activate nitrification in activated sludge too.

Fig.1 recombinant N.europaea

Fig.2 luminescence intensity

Fig. 3 residual ammonium concentration