Biological nitrogen removal capability and pathways analysis of a novel low C/N ratio heterotrophic nitrifying and aerobic denitrifying bacterium (Bacillus thuringiensis strain WXN-23)

A novel heterotrophic nitrification and aerobic denitrification (HNAD) bacteria, identified as Bacillus thuringiensis strain WXN-23, was isolated from husk feed filtrate of a pig farm. It was the first report of Bacillus thuringiensis with the capability for HNAD and could adapt to the condition of low Carbon/Nitrogen (C/N) ratio. Nitrogen could be efficiently removed by the strain WXN-23 in simulated wastewater, be it in single or mixed form nitrogen sources. The nitrogen balance revealed that 63.5% of the initial nitrogen (5.32 mg) was lost in the form of N-2. The conditions for maximum total nitrogen (TN) removal efficiency (95.996%) were shaking speed of 126.89 r/min, a carbon C/N ratio of 5.91, the temperature of 32.81. C, and a pH value of 8.17. The nitrification-denitrification metabolic pathway (NH4+-N -> NH2OH -> NO2--N -> NO3--N -> NO2--N.NO -> N2O -> N-2) under aerobic conditions was determined on the basic of characteristic of N removal, N balance analysis, enzyme assay and functional genes amplification results. Strain WXN-23 was effective at wastewater treatment, with TN, NH4+-N, NO3--N and NO2--N removal efficiencies of 82.12%, 86.74%, 90.74% and 100%, respectively.

Automated summary

A novel heterotrophic nitrification and aerobic denitrification (HNAD) bacteria, Bacillus thuringiensis strain WXN-23, was isolated from husk feed filtrate of a pig farm. It could efficiently remove nitrogen in simulated wastewater, adapt to low C/N ratio conditions, and showed a nitrogen balance efficiency of 63.5% in the form of N-2. The most optimal conditions for total nitrogen removal were shaking speed of 126.89 r/min, C/N ratio of 5.91, temperature of 32.81. C, and pH value of 8.17. The nitrification-denitrification metabolic pathway under aerobic conditions was determined, and strain WXN-23 exhibited high removal efficiencies for TN, NH4+-N, NO3--N and NO2--N in wastewater treatment.