Nitrogen removal characteristics and potential application of the heterotrophic nitrifying-aerobic denitrifying bacteria Pseudomonas mendocina S16 and Enterobacter cloacae DS′5 isolated from aquaculture wastewater ponds

Two biosafety strains, identified as Pseudomonas mendocina S16 and Enterobacter cloacae DS'5, were isolated from freshwater aquaculture ponds and showed significant heterotrophic nitrification-aerobic denitrification abilities. Within 48 h, the inorganic nitrogen removal efficiencies in the two strains were 66.59 %-97.97 % (S16) and 72.27 %-96.44 % (DS'5). The optimal conditions for organic nitrogen removal of the two strains were temperature 20-35 degrees C and carbon/nitrogen (C/N) ratio 10-20 while using sodium citrate as the carbon source. Sequence amplification demonstrated the presence of the denitrification genes in both the two strains, and quantitative real-time PCR results showed that the coupled expression of nap + nar would improve the nitrate removal rate in S16. The nitrogen removal efficiencies of the two strains in immobilization culture systems were 79.80 %-98.58 % (S16) and 60.80 %-98.40 % (DS'5). This study indicated the great potential application of the two strains in aquaculture tail water treatment.