Isolation And Characteristics Of Three Aerobic Denitrifying Bacteria

Aerobic denitrifying bacteria play an important role in the biological nitrogen removalprocess. However, there were few studies on aerobic denitrifying bacteria. the isolation andcharacteristics of aerobic denitrifying bacteria with high nitrite removing ability fromenvironmental samples were investigated.In this paper,11strains of aerobic denitrifying bacteria were isolated from mangrove soiland shrimp ponds with silicate plate and DM plate. Three strains F4, F6and F7with goodperformances has been selected by nitrite removing ability experiment. According to themorphological observation, pysiological biochemical test and sequence analysis of the16SrDNA, strain F4was identified as Pseudomonas sp.; strain F6was identified as Paracoccus sp.;strain F7was identified as Pseudomonas sp.Under aerobice conditions, three strains of aerobic denitrifying bacteria were all playedgood performance of nitrite removal efficiency.The denitrifying experiment results showed thatthe reduction efficiency of three strains F4, F6and F7within48hours could reach to47%,64%,45%, respectively with initial nitrite concentration of2500mg/L.DM medium was based, further added diffierent metal ions, carbon and nitrogen sources. Thedifferent ecological factors which affecting the denitrifacation efficiency of three strains werediscussed to get the optimal nitrite degradation conditions. The ecological factors containing C/N,initial pH, temperature and so on.The experiment results showed that three strains F4, F6and F7could also grow and showed aerobic denitrification ability in the medium containing seignette salt,sodium acetate, sodium succinate or sodium citrate as the sole carbon source, and seignette saltwas the most effeetive one. As the C/N rate was less than12, the removal rate of the NO₂-Nincreased rapidly with the inerease of the C/N rate in cultural medium. More over, the resultsshowed that the best pH was the weak alkaline, the best temperature for three strains was rangedfrom25℃to30℃. Aerobic denitrifacation rate decreased with the increase of the nitriteconcentration from1000to3000mg/L in cultural medium. Though three strains of aerobicdenitrifying bacteria strain were all strongly inhibited by ions Pb²⁺, Hg²⁺and Cr⁷⁺, and theprocess of aerobic denitrification was activated by ions of Cu²⁺, Zn²⁺and Fe³⁺with lowconcentration.The bacteriostatic activity in the metabolite of three bacterial strains was detected by way ofoxford cup double layer flat quantitative diffusion detection, the results showed that metabolite had not bacterioststic activity against Staphylococcus aureus and E.Coli. the antibiotic sensitivitytests showed that the aerobic denitrifying bacteria strain F4and F7were more insensitive toantibiotics. According to analyse the bacterias F4metabolite by GC/MS, the test results indicatedthat metabolite contained bacteriochlorophyll.By orthogonal designed, optimization the culture conditions for strain F6. Finally come tothe optimal combination of medium were: seignette salt2%, and potassium nitrite0.25%,K₂HPO₄0.6‰, MgSO₄·7H₂O0.2‰, MnSO₄·H₂O0.01‰. The culture conditions in the optimalcombination were: culture fermentation temperature was30℃;inoculum was5%; shaker180r/min for48h.Entrapping methods with sodium alginate（SA） carrier were studied.The results showed thatthe optimization of immobilization carrier when the concentrations of SA, active carbon andCaCl₂were4%,1.5%and4%respectively. The kind of immobilization beads with SA, calciumchioride and activated carbon carrier were made of denitrifying bacteria F6. Then the feasibilityof nitrite removal in aquaculture wastewate by the immobilization beads was studied. Comparedwith free baeteria group, immobilized group has showed greater removal efficiency of nitrite inaquaculture water treatment process. The everage gain and superoxide dismutase of immobilizedgroup were both greater than free baeteria group. Immobilized group could improved the pH ofaquaculture water.