Screening And Identification Of 2,4-xylenol-degrading Bacteria And Its Degradation Characteristics

Alkylphenol compounds are one of the common endocrine disruptors and important ingredients of synthetic chemicals,which have a great impact on the environment,animals,plants and human beings.The discharge of alkylphenol compounds into the environment directly threatens the security of the ecosystem.As one of the alkylphenol compounds,2,4-xylenol has become one of the organic pollutants in the control of the world.The vapor of2,4-xylenol can stimulate the eyes,skin and respiratory system,which can cause symptoms such as headache,nausea,abdominal pain,coma and other symptoms when taken or absorbed through the skin.And its direct discharge can harm the environment even cause the pollution to the water body and the atmosphere.In this study,a bacteria which can use 2,4-xylenol as the only carbon source and energy source was screened from the sludge in the lower reaches of huxi river in Huazhong University of Science and Technology.The 16S r RNA gene was amplified by Polymerase Chain Reaction(PCR)and identified as Rhodococcus sp.24714.The study showed that the bacteria was resistant to ampicillin and naphthalidonic acid,and the maximum degradation of concentration of 2,4-xylenol was 4.5 m M,and the bacteria can degrade 2m M 2,4-xylenol within 36 h.In this study,influence factors and the degradation kinetic characteristics have been studied.The carbon source analysis of the bacteria and LC-MS analysis of the degradation solution during the degradation process were carried out to speculate the biodegradation pathway of 2,4-xylenol.The result showed that the most suitable conditions for the growth of the bacteria were determined as follows:the temperature was 30?,the p H was 7.The degradation rate of 2,4-xylenol can reach 100%at p H 8 within 42 h which was significantly higher than that at p H 6,indicating that the bacteria is suitable for growth in neutral or weakly alkaline environments.The result also showed that the degradation rate of the process would increase with the increase of the concentration of the initial bacterial solution.Logistic model and Haldane model were used to simulate the kinetics of cell growth and substrate degradation when the bacteria screened in this study growing with2,4-xylenol which the bacteia used as the only carbon source and energy source.And Matlab was used to regression the parameters of the model.By comparing the model value with the experimental value,we found that the model and experimental results fit well.Rhodococcus sp.24714 still can use protocatechuic acid,gentian acid as the sole carbon source growth,which can be speculated that the bacteria in this study may have gentian acid 1,2-dioxygenase,protocatechuic acid 3,4-or 4,5-dioxygenase,and can successfully express them.The degradation intermediates of 2,4-xylenol which were determined by LC-MS have showed that procatechuic acid is produced during degradation as a kind of intermediate products.This result indicated that The fourth methyl group of 2,4-xylenol gradually reacts to form hydroxymethyl group,aldehyde group and carboxyl group to form4-hydroxy-3-methylbenzoic acid,then The reaction is followed by the formation of 4-hydroxyphlorophthalic acid,followed by the formation of the intermediate metabolite procatechuic acid.2,4-xylenol was not oxidized to CO₂ and H₂O in this study.