Enhanced nitrous oxide production in denitrifying dechloromonas aromatica strain RCB under salt and alkaline conditions = Dechloromonas aromatica strain RCB의 탈질 반응에서 염 농도 및 pH가 $N_2O$ 배출에 미치는 영향에 대한 연구
Salinity and pH are important environmental parameters with direct and indirect impacts on viability and metabolism of microorganisms. In this study, the effects of salt and alkaline stress on the kinetic balance between $N_2O$ production and consumption in the denitrification pathway of Dechloromonas aromatica strain RCB were examined. $N_2O$ accumulated transiently only in insignificant amounts at low salinity (≤0.5% NaCl) and circumneutral pH (7.0 and 7.5). Incubation at 0.7% salinity resulted in substantially longer lag phase and slower growth rate, along with the increase in the amounts of transiently accumulated $N_2O$ (15.8±2.8 µmoles $N_2O$-N/vessel). Incubation at pH 8.0 severely inhibited growth and resulted in permanent accumulation of 29.9±1.3 µmoles $N_2O$-N/vessel from reduction of 151±20 µmoles $NO_3^-$. The transcription analyses observed decreased nosZ/($nirS_1+nirS_2$) ratios coinciding with $N_2O$ accumulation. The $N_2O$ consumption rates of resting D. aromatica cells subjected to the salt and or alkaline stress conditions were significantly lower than the rates of $N_2O$ production from $NO_2^-$ reduction at $N_2O$ / $NO_2^-$ concentration of 0.1 mM, but not at a higher concentration (1.0 mM). Thus, alteration in $N_2O$ consumption kinetics was another reason for enhanced $N_2O$ production observed under the stress conditions. The findings in this study suggest that canonical denitrifiers may be a significant $N_2O$ source when faced with abrupt environmental changes.