Preliminary results:The in vitro assessment of the impact of ethoxyquin (EQ) on the activity and growth of two representative strains of terrestrial ammonia-oxidizing bacteria (AOB)(Nitrosomonas europaea, Nitrosospira multiformis) in liquid cultures, has been completed so far. EQ showed a persistent inhibitory effect on the growth and function of the selected AOB strains at concentration levels of 460 μM. The effect imposed to N. multiformis was equivalent but more persistent to the impact of the well-known nitrification inhibitor nitrapyrin which is a first indication for the potential utilization of EQ as nitrification inhibitor. Measurements of the metabolism of EQ in the liquid cultures suggested a rapid transformation to quinone imine (QI) which concurred with the appearance of the inhibitory effects on AOB. Following the dissipation of ethoxyquinin the liquid cultures of ammonia-oxidizers we found that EQ was transformed to QI and this transformation concurred with the onset of inhibition.
Immediate future work: In vitro culture experiments will be performed to further explore the effects of the two EQ oxidation derivatives, QI and EQNL, on the growth and nitrification of AOB species Nitrosomonas europaea and Nitrosospira multiformis. The same set of in vitro tests (EQ and its derivatives separately) will be also conducted with two AOA terrestrial representative species Nitrosotalea sinensis and Nitrosocosmicus franklandus in order to explore the inhibitory effect of EQ and its derivatives on AOA. Tested concentrations of EQ oxidation derivatives, QI and EQNL, will be chosen based on the dissipation pattern of EQ observed in the sterile liquid cultures.