ABSTRACT
This study investigated the effects of ammonium and nitrite on ammonia-oxidizing bacteria (AOB) from an activated sludge process in laboratory-scale continuous-flow reactors. AOB communities were analyzed using specific PCR followed by denaturing gel gradient electrophoresis, cloning and sequencing of the 16S rRNA gene, and AOB populations were quantified using real-time PCR. To study the effect of ammonium, activated sludge from a sewage treatment system was enriched in four reactors receiving inorganic medium containing four different ammonium concentrations (2, 5, 10 and 30 mM NH(4) (+)-N). One of several sequence types of the Nitrosomonas oligotropha cluster predominated in the reactors with lower ammonium loads (2, 5 and 10 mM NH(4) (+)-N), whereas Nitrosomonas europaea was the dominant AOB in the reactor with the highest ammonium load (30 mM NH(4) (+)-N). The effect of nitrite was studied by enriching the enriched culture possessing both N. oligotropha and N. europaea in four reactors receiving 10-mM-ammonium inorganic medium containing four different nitrite concentrations (0, 2, 12 and 22 mM NO(2) (-)-N). Nitrosomonas oligotropha comprised the majority of AOB populations in the reactors without nitrite accumulation (0 and 2 mM NO(2) (-)-N), whereas N. europaea was in the majority in the 12- and 22-mM NO(2) (-)-N reactors, in which nitrite concentrations were 2.1-5.7 mM (30-80 mg N L(-1)).
