AUTHOR=Thandar Soe Myat , Ushiki Norisuke , Fujitani Hirotsugu , Sekiguchi Yuji , Tsuneda Satoshi 

TITLE=Ecophysiology and Comparative Genomics of Nitrosomonas mobilis Ms1 Isolated from Autotrophic Nitrifying Granules of Wastewater Treatment Bioreactor

JOURNAL=Frontiers in Microbiology

VOLUME=7

YEAR=2016

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2016.01869

DOI=10.3389/fmicb.2016.01869

ISSN=1664-302X

ABSTRACT=<p>Ammonia-oxidizing bacteria (AOB), which oxidize ammonia to nitrite in the first step of nitrification, play an important role in biological wastewater treatment systems. <italic>Nitrosomonas mobilis</italic> is an important and dominant AOB in various wastewater treatment systems. However, the detailed physiological and genomic properties of <italic>N. mobilis</italic> have not been thoroughly investigated because of limited success isolating pure cultures. This study investigated the key physiological characteristics of <italic>N. mobilis</italic> Ms1, which was previously isolated into pure culture from the nitrifying granules of wastewater treatment bioreactor. The pure culture of <italic>N. mobilis</italic> Ms1 was cultivated in liquid mineral medium with 30 mg-N L<sup>-1</sup> (2.14 mM) of ammonium at room temperature under dark conditions. The optimum growth of <italic>N. mobilis</italic> Ms1 occurred at 27°C and pH 8, with a maximum growth rate of 0.05–0.07 h<sup>-1</sup>, which corresponded to a generation time of 10–14 h. The half saturation constant for ammonium uptake rate and the maximum ammonium uptake rate of <italic>N. mobilis</italic> Ms1 were 30.70 ± 0.51 μM NH<sub>4</sub><sup>+</sup> and 0.01 ± 0.002 pmol NH<sub>4</sub><sup>+</sup> cells<sup>-1</sup> h<sup>-1</sup>, respectively. <italic>N. mobilis</italic> Ms1 had higher ammonia oxidation activity than <italic>N. europaea</italic> in this study. The oxygen uptake activity kinetics of <italic>N. mobilis</italic> Ms1 were K<sub>m(O<sub>2</sub>)</sub> = 21.74 ± 4.01 μM O<sub>2</sub> and V <sub>max(O<sub>2</sub>)</sub> = 0.06 ± 0.02 pmol O<sub>2</sub> cells<sup>-1</sup> h<sup>-1</sup>. Ms1 grew well at ammonium and NaCl concentrations of up to 100 and 500 mM, respectively. The nitrite tolerance of <italic>N. mobilis</italic> Ms1 was extremely high (up to 300 mM) compared to AOB previously isolated from activated sludge and wastewater treatment plants. The average nucleotide identity between the genomes of <italic>N. mobilis</italic> Ms1 and other <italic>Nitrosomonas</italic> species indicated that <italic>N. mobilis</italic> Ms1 was distantly related to other <italic>Nitrosomonas</italic> species. The organization of the genes encoding protein inventory involved in ammonia oxidation and nitrifier denitrification processes were different from other <italic>Nitrosomonas</italic> species. The current study provides a needed physiological and genomic characterization of <italic>N. mobilis</italic>-like bacteria and a better understanding of their ecophysiological properties, enabling comparison of these bacteria with other AOB in wastewater treatment systems and natural ecosystems.</p>