Isolation and characterization of three heterotrophic nitrifying-aerobic denitrifying bacteria from a sequencing batch reactor

Three novel heterotrophic nitrifying bacterial strains, YB, YH and YL were isolated from a laboratory-scale sequencing batch reactor. These strains were identified as Acinetobacter junii YB, Pseudomonas putida YH and Pseudomonas aeruginosa YL, respectively. All three strains exhibited efficient heterotrophic nitrification-aerobic denitrification capabilities, with a low accumulation of nitrification products over a wide range of ammonium loads, and were able to utilize nitrite and nitrate as a sole nitrogen source. About one-half of the consumed total nitrogen was converted into intracellular nitrogen, and the remainder was believed to be denitrified. Strain YH was found to possess higher nitrogen removal capacity than the other two strains. Single-factor experiments indicated that the optimal conditions for all three heterotrophic ammonium oxidation strains were as follows: succinate as the carbon source, C/N ratio of 10, pH of 7.0, temperature of 30 °C, and shaking speed of 160 rpm. The presence of hydroxylamine oxidase, nitrite reductase and nitrate reductase provided additional evidence of heterotrophic nitrification and aerobic denitrification of the isolates. Higher enzyme activity observed in strain YH further demonstrated its superior nitrogen removal ability.