Assessment of denitrifying bacterial composition in activated sludge

► nosZ gene was in the range of 104-106 and nirS gene with 104-105 copy number per ml of sludge. ► Betaproteobacteria were found to numerically dominate the sludge habitat. ► Some isolates showed efficient denitrification, while others accumulated nitrite during denitrification. ► The results also indicate presence of different truncated denitrifiers with high numbers in sludge habitats.