Screening And Degradation Characteristics Of Pyridine-degrading Bacteria

Wastewater from pesticides,coking and pharmaceuticals generally contains high concentrations of pyridine.Pyridine is a nitrogen-containing heterocyclic compound.It is listed as a priority pollutant for its teratogenic,carcinogenic and mutagenic properties and has attracted the attention of environmental researchers.In recent years,the removal of pyridine from wastewater using microorganisms,especially screening and culturing efficient degrading bacteria,has become a research hotspot.This thesis addresses the degradation of pyridine in wastewater under high salt conditions.The effect of different temperature,pyridine concentration and high salinity on the degradation of pyridine in the wastewater was investigated,and the pathways of the two strains to degrade pyridine were analyzed by UV,GC-MS and LC-MS.The following main conclusions were drawn from the study.(1)Six strains were successfully domesticated and isolated from the activated sludge of a wastewater biological treatment tank of a pesticide plant in Hunan Province,and three strains were named PDX01,PDX02 and PDX03,which can tolerate high concentrations of pyridine degradation.PDX03 is a new strain with the ability to degrade high concentrations of pyridine.(2)PDX02 and PDX03 are well tolerated to ambient temperature,p H and pyridine concentrations,but their tolerance ranges are slightly different.At an initial pyridine concentration of 1000 mg/L,PDX02 and PDX03 completely degrade the pyridine in the temperature range of 20°C to 40°C within 64 h and 96 h,respectively;at p H 5-10,PDX02 completely degrades the pyridine within 48h;at p H 6-9,PDX03 completely degrades the pyridine within 88 h.At a pyridine concentration of 2000 mg/L,the degradation rates of PDX02 and PDX03 at 88 h were 100% and 73%,respectively.(3)PDX02 and PDX03 can treat pyridine wastewater containing high concentrations of salts such as sodium chloride,sodium nitrate and sodium sulfate.At a pyridine concentration of 1000 mg/L,both strains were able to completely degrade the pyridine within 56 h at a sodium chloride concentration of 50 g/L.PDX02 and PDX03 completely degrade the pyridine within 48 h and 72 h,respectively,at a sodium nitrate concentration of up to 60g/L.PDX02 completely degraded the pyridine within 56 h at a sodium sulfate concentration of 50g/L,while PDX03 completely degraded the pyridine in a shorter time with increasing sodium sulfate concentration,which was 16 h shorter at 50g/L than at 5g/L.(4)By fitting the effects of pyridine on the growth of PDX02 and PDX03 to the kinetic equations of inhibition(Haldane,Yano,Webb and Aiba equations)and non-inhibition(Monod equation),it was found that the kinetics of the effects of pyridine on the growth of the two strains were consistent with the kinetic equations of inhibition;as the concentration of pyridine increased from 500 mg/L to-2000 mg/L,the specific growth rate of PDX02 decreased,while the specific growth rate of PDX03 showed a tendency to increase and decrease.(5)The detection of the intermediate products of the pyridine degradation process by UV,GC-MS,LC-MS,and the determination of the activity of the characteristic enzymes in bacteria during the pyridine degradation process,and the preliminary determination of the PDX02 degradation of pyridine by direct loop opening,and the possible pathways for the PDX03 degradation of pyridine by bacteria are mainly the hydroxylation,carboxylation and carbonylation of pyridine.