Shortcut nitrification of sludge by recombinant Escherichia coli overexpressing nitrite reductase

Abstract:

[Objective] To highlight the significance of nitrite reductase in wastewater denitrification and shortcut nitrification, we studied wastewater denitrification by Escherichia coli expressing nitrite reductase.[Methods] Nitrite reductase was overexpressed by transformed a recombinant plasmid with nir gene in E. coli. Expression of nitrite reductase and metabolism of nitrite were studied by detecting the products in the whole cell of recombinant E. coli. To evaluate the function of recombinant E. coli used for shortcut nitrification, we measured the denitrification efficiency of the mixture consisting of the recombinant E. coli and YF14 that was a nitrifying and denitrifying bacterium.[Results] The recombinant E. coli could express nitrite reductase, reduced about 1 mmol/L nitrite within 2 hours and produced almost equal amounts of nitric oxide (OD₆₀₀=2.0 bacterial suspension). When the recombinant E. coli and YF14 were mixed in equal proportions, the ammonia nitrogen removal efficiency increased by about (36.0±7.4)% within 12 hours, and the maximum accumulated amount of nitrite decreased by about 37%. Recombinant E. coli (OD₆₀₀=1.0) significantly improved the ammonia nitrogen removal efficiency of activated sludge by about (31.0±5.7)% within 12 hours, and no nitrite and nitrate were detected. Oxygen supply affected ammonia nitrogen removal with optimal DO of (6.4±0.7) mg/L.[Conclusion] Recombinant E. coli with nitrite reductase can contribute to the shortcut nitrification capacity of wastewater.