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(-)→N₂. 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 °C, where initial pH and temperature had the largest influence on ammonium removal.