Heterotrophic nitrification and aerobic denitrification at low nutrient conditions by a newly isolated bacterium, Acinetobacter sp SYF26

A new strain, named SYF26, was isolated from the Hei He oligotrophic drinking-water reservoir in China. Based on its phenotypic and phylogenetic characteristics, the isolate was identified as a species of genus Acinetobacter. Strain SYF26 was able to grow at low NH4+-N concentrations (5.46 mg l(-1)), and the nitrification rate was 0.064 mg NH4+-N l(-1) h(-1). Low accumulation of nitrate and nitrite was observed throughout the ammonium removal experiment. Strain SYF26 reduced NO3--N or NO2--N. Nitrite reductase and periplasmic nitrate reductase were detectable. The putative nitrogen removal process carried out by the strain SYF26 is as follows: NH4+-> NH2OH -> NO2--> NO3-, then NO3--> NO2--> N-2. Response surface methodology analysis demonstrated that the maximum removal of ammonium occurred under the following conditions: NH4+-N concentration of 22.05 mg l(-1), C/N ratio of 4.31, initial pH of 7.78 and temperature of 29.73 degrees C, where initial pH and temperature had the largest influence on ammonium removal.