| Phenol is a widely distributed organic pollutant in the water environment.It has the characteristics of high toxicity,difficult degradation and strong carcinogenicity.Biological treatment of phenol-containing wastewater has received extensive attention due to its high efficiency and environmental friendliness.The application of a single biosurfactant or a single highly efficient degrading bacteria has a certain effect on the treatment of phenol wastewater.However,there are still relatively few studies on the efficient degradation of phenol by biosurfactant-producing strains.Therefore,it is of great practical significance to explore the phenol degradation characteristics and mechanism of biosurfactant-producing strains for the treatment of phenol-containing wastewater.In this study,the phenol degradation potential and mechanism of two rhamnolipid-producing strains Pseudomonas aeruginosa CT5 and CT7were preliminarily analyzed,and the optimal phenol degradation conditions were optimized by single factor experiment,PB experiment and BB experiment.The path of phenol degradation by the strain was determined by enzyme specific activity.In addition,the key differential genes and metabolic pathways of phenol degradation by strain CT7 were analyzed by transcriptome sequencing.The specific experimental results are as follows:（1）The strains CT5 and CT7 were inoculated into the inorganic salt medium with 100mg/L phenol,and the continuous subculture was stopped when the phenol concentration was500 mg/L;the highest phenol degradation rates of domesticated strains CT5 and CT7 were25.21%and 26.22%respectively in the medium with 300 mg/L phenol as the sole carbon source.The degradation rate of phenol increased to 42.12%and 48.62%after adding soybean oil co-existing carbon source.（2）The culture conditions of strain CT5 degrading 300 mg/L phenol were determined by single factor optimization experiment as follows:soybean oil 10%,KNO38 g/L,KH2PO40.08 g/L,Na2HPO40.04 g/L,inoculation amount 4%,MgSO40.2 g/L,CaCl2100 mg/L,FeCl34 mg/L.The phenol degradation rate was 69.82%after 144 h.The culture conditions of strain CT7 degrading 300 mg/L phenol were as follows:corn oil 8%,NaNO38 g/L,KH2PO40.08 g/L,Na2HPO40.04 g/L,inoculation amount 4%,MgSO40.30 g/L,CaCl250 mg/L,FeCl36.00 mg/L.The degradation rate of phenol was 70.91%after 144 h.（3）It was found that the degradation rate of strain CT5 and CT7 was the highest at 200mg/L phenol concentration.The optimal degradation conditions of CT5 optimized by response surface methodology were as follows:KNO37.62 g/L,inoculum 3.86%,MgSO40.21 g/L,and the degradation rate reached 79.16%in 144 h,which was 2.29 times higher than the degradation rate of 34.52%with 200 mg/L phenol as the sole carbon source before optimization.The optimum degradation conditions of strain CT7 were as follows:corn oil 8.29%,NaNO38.27 g/L,CaCl256.64 mg/L,and the degradation rate reached 83.45%at 144h.The degradation rate of phenol after optimization was 2.37 times higher than that before optimization when 200 mg/L phenol was used as the sole carbon source.（4）By analyzing the phenol degradation pathway,it was found that in the presence of co-metabolism carbon source,only the change of absorbance was detected at the wavelength of 260 nm,and the change of absorbance was not detected at the wavelength of 375 nm.The phenol degradation pathway of strains CT5 and CT7 was ortho ring opening of catechol under the catalysis of C12O enzyme to generate cis,cis-hexadienedicarboxylic acid.（5）Comparative transcriptome analysis showed that compared with the control group with corn oil as the sole carbon source,strain CT7 significantly up-regulated 1155 differential genes and significantly down-regulated 990 differential genes in the corn oil and phenol co-metabolism carbon source treatment group.KEGG metabolic pathway analysis of differential genes showed that multiple pathways including ABC transporter,membrane transport,amino acid metabolism,carbohydrate metabolism,lipid metabolism and energy metabolism were significantly different. |
