PI-140:

Physiological characterization of Nitrosomonas mobilis-like strain isolated from autotrophic nitrifying granule

Nitrification is an important step in biological wastewater treatment system. In bioreactors, nitrifying granules are produced to improve nitrification by preserving the nitrifying bacteria namely ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria. Nitrosomonas mobilis is the important and dominant AOB in nitrifying granules. Up to date, the detailed physiological and biochemical properties of N.mobilis have not been well studied because of the limited numbers of success in the isolation of pure cultures. In our previous study, pure culture of N.mobilis, namely Ms1, was isolated from the nitrifying granules. In this study, the key physiological characteristics of N.mobilis Ms1 were investigated. The pure culture was incubated in liquid mineral medium with 30 mg/L (2.14 mM) ammonium chloride at room temperature under dark condition. In the culture medium, Ms1 grew as densely packed micrococolonies together with single cells when observed with a fluorescence microscope. Microcolony was the spherical shape colony of at least four aggregated single cells and the size ranged from 2-5 μm for the small microcolony. Temperature and pH ranges for ammonia oxidation of Ms1 were 17-37 _C and 6-9, respectively, and 27 _C and pH 8 were shown as the optimum. Ms1 could oxidize well at the ammonium concentrations of up to 35.7 mM. The maximum specific growth rate (μ_max) was 0.04-0.06 h^-1, with the doubling time of 11-14 hours. The K_m and V_max values calculated from the measured values of ammonia oxidation activity of Ms1 were 45-55 μM and 0.22-0.25 pM cells^-1 h^-1, respectively. This study provides the better understanding of N.mobilis to compare with the other AOB and to continue study their genetic characteristics. As the future work, we conduct the genomic analysis and RNA sequencing of N.mobilis Ms1 to explore the novel function of the genes, proteins or other molecules that are involved in the microcolony formation.

keywords:Ammonia-oxidizing bacteria,pure culture,*Nitrosomonas mobilis*,physiological characteristics