Metabolic engineering enhances the nitrogen removal by Paracoccus denitrificans DYTN-1

Abstract:

[Objective] Paracoccus denitrificans is an environment-friendly strain of α-Proteobacteria.It can also perform denitrification under aerobic conditions and has good denitrification ability.This study intended to use P.denitrificans DYTN-1 as the chassis cell to screen nitrogen inducible promoters for strengthening the nitrification and denitrification pathways,thus achieving the purpose of enhancing the removal of nitrogen pollutants by metabolic engineering.[Methods] Recombinant plasmids overexpressing amoA,amoB,hao and nirS genes were introduced into P.denitrificans DYTN-1 cells by conjugation.The gene elements and nitrogen removal ability of P.denitrificans DYTN-1 were characterized by fluorescence quantitative detection and nitrogen quantitative detection.[Results] Six promoters induced by NO₂^‒,NO₃^‒ and NH₄⁺ were obtained at 2 to 26-fold induction.The residual amount of NO₃⁻ in the medium of the nirS overexpressed strain was 67% of that of the wild-type strain after treatment with 2 g/L KNO₃for 24 h.The strains overexpressing both hao and nirS had only 50% of the residual NO₃⁻ of the wild-type strain after treatment with 1 g/L NH₄Cl and 2 g/L KNO₃ for 12 h.Furthermore,the final degradation efficiency of total nitrogen reached 79.5% and the residual total nitrogen was only half of that of the wild-type strain.[Conclusion] It is feasible to carry out metabolic engineering with the aboved screened promoters to enhance the removal of nitrogen pollutants in P.denitrificans DYTN-1.