Identification and denitrification performance of an efficient aerobic denitrification bacterium Pseudomonas gessardii YZ-7

【Objective】 The efficient aerobic denitrification bacteria were screened to develop new strains with strong denitrification ability suitable for application in shrimp ponds, so as to solve the problem of eutrophication caused by excessive nitrogen content in shrimp ponds.【Method】 An efficient aerobic denitrification bacterium was isolated and screened from shrimp pond sewage sludge and water samples by diluted method in Giltay differential medium. Then it was identified by morphological characteristics, physiological and biochemical characteristics and 16S rDNA sequence analysis. Furthermore, the denitrification efficiency of the isolated strain under KNO₃ as nitrogen source was determined, and the effects of different environmental conditions on denitrification performance of the isolated strain was analyzed. Finally, the denitrification ability of the strain in shrimp pond aquaculture waste water was evaluated by simulation test.【Result】 An efficient denitrification bacterium was isolated from shrimp pond sewage sludge and water samples. It was identified as Pseudomonas gessardii by morphological characteristics, physiological and biochemical characteristics and 16S rDNA sequence analysis, and named YZWF2207(YZ-7). When KNO₃ was used as the sole nitrogen source, strain YZ-7 entered the logarithmic growth phase after a 6 h lag period, with the growth rate of the strain YZ-7 closely related to the removal rate of nitrogen-containing substances. When sodium citrate was used as the solecarbon source, the removal rate of nitrate nitrogen(NO₃^--N) was 99.05%. When the carbon/nitrogen ratio(C/N) ranged from 4.42 to 5.00, strain YZ-7 had relatively high NO₃^--N removal rate(99.71%-99.85%). The highest NO₃^--N removal rate of strain YZ-7 was not synchronized with the maximum biomass. And it was more suitable to living in weak alkaline environment(pH 7.0-8.0). The appropriate ambient temperature of strain YZ-7 was 30℃ though, the denitrification process could be completed efficiently at low temperature(15℃), and the NO₃^--N removal rate could reach 79.41%. Strain YZ-7 had extremely significant effect on NO 3--N removal from shrimp pond aquaculture wastewater(P<0.01), and the accumulated nitrite nitrogen(NO₂^--N) had obvious downward trend compared with the control group.【Conclusion】 An efficient aerobic denitrification bacterium P. gessardii(YZ-7) is isolated from shrimp pond sewage sludge and water samples. The optimum carbon source for aerobic denitrification performance is sodium citrate, with the C/N ratio of 4.42-5.00, pH of 7.0-8.0, and the temperature of 30℃. The strain YZ-7 has strong denitrification ability and competitiveness in aquaculture wastewater treatment. As an aerobic denitrification bacterium, it has broad application prospects in the research and development of denitrification biological products in nitrogen-rich aquaculture water.