Identification of a denitrifying polyphosphate-accumulating organism (DPAO) and study on its denitrifying functional genes

A denitrifying polyphosphate-accumulating organism (DPAO) was isolated and identified, and the denitrifying functional genes were investigated. The strain ZQN2 was isolated using denitrifying medium. It was distinguished as DPAO by tests of aerobic phosphorus uptake, nitrate reduction, metachromatic granules and PHB (poly-β-hydroxybutyrate) granules dyeing. Test of anaerobic phosphorus release/anoxic phosphorus uptake showed that strain ZQN2 released phosphorus and synthesized PHB at the anaerobic phase and used NO₃^- as acceptor to oxidize PHB during the anoxic phase with luxury phosphorus uptake, performing the function of simultaneous denitrifying phosphorus removal. The 16S rRNA gene sequence of strain ZQN2 was used for homology analysis and construction of phylogenetic trees. The results suggested that the 16S rRNA gene sequence of ZQN2 had up to 99% homology with those of many strains of Bacillus cereus strains in GenBank database. With physiological and biochemical reactions, the strain ZQN2 was identified as Bacillus cereus. The result of denitrifying functional gene study suggested that strain ZQN2 was the type of nirS⁺ and nirK^-, which confirmed its denitrifying function from molecular biology point of view. Moreover, the phylogenetic analysis of nirS gene of ZQN2 showed that it was closely related to many strains of Pseadomonas aeruginosa, which was different from the analysis results of the 16S rRNA.