Isolation And Degradation Characteristics Of BaP-Degrading Mixed Bacteria From Rice Rhizosphere

Polycyclic aromatic hydrocarbons(PAHs)are a type of persistent organic pollutants widely distributed in the environment.After entering the environment,PAHs migrate with the food chain and cause harm to human health.Bioremediation conforms to the concept of green development and is the most frequently used remediation technology for PAHs pollution in the environment.Microbial remediation plays an important role in bioremediation.It was found that mixed bacteria repair of PAHs had better effect and stronger adaptability than single bacteria.Benzo[a]pyrene(BAP)is one of the most toxic PAHs and the earliest known chemical carcinogen.For highly toxic and difficult to degrade BAP,the screening cycle of degrading microorganisms is long and the effect is not good,which has become a major problem for soil remediation.In this paper,using benzo[a]pyrene as the selective pressure,three strains of degrading bacteria with high degradation potential were selected from the rhizosphere of rice planted near an oil field,and the degradation ability and characteristics of the three strains under mixed conditions were investigated.The main research was The results are as follows:(1)With benzo[a]pyrene as the only carbon source,the concentration of the carbon source was gradually increased,and three BaP-degrading bacteria with the ability to degrade BaP were successfully screened.After identification of morphology,molecular biology and physical and chemical properties,they were named Stenotrophomonas maltophilia SY-1(culture preservation number CCTCC M 2020310),Bacillus sp.SY-2(culture preservation number CCTCC M 2020309),Ochrobactrum tritici SY-3(culture preservation number CCTCC M 2020308).(2)The ability of mixed degrading bacteria to degrade benzo[a]pyrene,pyrene and benzofluoranthene in a liquid system and the degradation ability of benzo[a]pyrene in a soil system were explored.The results show that the mixed degradation bacteria can degrade 10mg/L and 50 mg/L BaP at 68.36%and 57.02%respectively within 28 days;for 100 mg/L benzo[a]pyrene,pyrene and benzofluorine For anthracene,the 28-day degradation rate was35.37%,30.88%,and 10.05%;the degradation rate of benzo[a]pyrene at a concentration of100 mg/kg reached 16.15%within 56 days in the artificially aged soil system for 6 months.(3)The factors affecting the degradation ability of BaP-degrading mixed bacteria were investigated.BaP-degrading mixed bacteria had little difference in the 7-day degradation rate of benzo[a]pyrene at the inoculation amount of OD₆₀₀=1.0 and OD₆₀₀=0.1.When p H=6,the degradation effect of BaP-degrading mixed bacteria is the best.When pyrene is added as a co-metabolism substrate of benzo[a]pyrene,the degradation of benzo[a]pyrene is inhibited to a certain extent,but it still has degradability and has a degradation effect on pyrene.(4)The metabolic pathway of BaP-degrading mixed bacteria to benzo[a]pyrene is speculated.GC-MS technology was used to detect the metabolic components of the first 1,4,7,14 and 28 days of the degradation process.It is preliminarily speculated that the metabolic process of BaP-degrading mixed bacteria may be caused by interaction between bacteria and aerobic metabolism.It is completed together,mainly through two pathways of metabolism of4,5-dihydrobenzo[a]pyrene and hept-4-ylisobutyl phthalate,and is initially converted into 2-naphthol and 3-Phenyl-1-propanol through enzymatic hydrolysis.Phenylpropanol,eugenol,etc.are then metabolized into o-cresol and phenol,then converted into muconic acid and fatty acids,and finally metabolized into glycerol,which can be completely mineralized into CO₂and H₂O in the cell.Through the above research,the BaP high-efficiency mixed degrading bacteria are obtained,the degradation products are thorough,and the degradation ability of pyrene and benzofluoranthene is also good;the degradation effect of the degrading bacteria in the complex soil system is better than the existing research,and the application prospect is broad.