Effect Of Metal Ions On Degradation Of Pyrene By Rhodococcus Ruber L9 And Its Mechanism Of Action

Polycyclic aromatic hydrocarbons(PAHs)are a kind of typical persistent organic pollutants with high toxicity,high biological concentration and difficult to degrade.Pyrene,as representative of the study of high-ring aromatics,is a stable tetraphenyl ring structure and organic matter.The research hotspot in the field of environmental science and technology has always been the microbial remediation method of polycyclic aromatic hydrocarbons.This method has been widely used in the removal of polycyclic aromatic hydrocarbons in the environment because of its low operating cost,no interference to the environment.Although the polycyclic aromatic hydrocarbon degrading bacteria existing in the natural environment are abundant,degradation ability of the polycyclic aromatic hydrocarbon pollutants under natural conditions is limited and the degradation rate is very low,because the distribution of pollutants in the natural environment is not concentrated.The degradation rate can be effectively increased by adding an appropriate concentration of metal ions.In this paper,the sole carbon source was pyrene,and the Rhodococcus ruber L9which was come from the soil contaminated by PAHs was used as the test strains.In the reaction system of degrading PAHs,four different metal ions(Fe³⁺,Ca²⁺,Cu²⁺and Mn²⁺)are added in order to increase the degradation rate of PAHs.The best one of metal ions for degradation promotion and its optimum concentrations were screened out.The change of enzyme(catechol 1,2-dioxygenase and catechol 2,3-dioxygenase)activity in the reaction system were studied.Furthermore,the change of the price of intracellular and extracellular metal ions has been analyzed,Therefore,the mechanism of the degradation of sputum by Rhodococcus ruber L9 erythropolis in the presence of Fe³⁺was inferred.The main research contents and results of the thesis are as follows:(1)Fe³⁺,Ca²⁺,Cu²⁺and Mn²⁺were added to the degrading system of Rhodococcus ruber L9 to find out the effects of different metal ions on the degradation of pyrene.It was found that the efficiency of degrading pyrene by Rhodococcus ruber L9 with Fe³⁺was differently increased in the range of 0.1mmol/L-0.3mmol/L,which were increased about 8%compared with the degradation rate of no metal ions;The efficiency of degrading pyrene by Rhodococcus ruberL9 was increased by about 12%when the concentrations of Mn²⁺were 0.1mmol/L-0.15mmol/L.(2)Under different concentrations of Fe³⁺,Mn²⁺,the growth of Rhodococcus ruberL9 and the change of pyrene degradation rate were studied.It was found that when 0.45mmol/L Fe³⁺was applied,the growth of bacteria was the best,and the degradation rate of pyrene was the highest,reaching 77%,compared with the control group,it was increased by 30%,which was inferred to be the best metal ion.(3)The effect of Fe³⁺on the degradation of phenol,pyrene,phenanthrene and anthracene by Rhodococcus ruberL9 has been studied.It was found that the degradation of phenol by Rhodococcus ruberL9 increased about 20%-50%,and the degradation rate increased about 24h.The degradation rate of anthracene increased about 3%-10%;the degradation rate of phenanthrene increased 10%-18%;the degradation rate of pyrene was 35%higher than that of the control group.(4)Protein production during the degradation of pyrene in the presence of Fe³⁺were studied.It was found that the total protein yield increased by about 30%after adding Fe³⁺.(5)The activity of catechol 1,2-dioxygenase(C120)and catechol 2,3-dioxygenase(C230)were analyzed,and their activities were significantly improved compared with the control group.(6)It was found that the changes of C120 and C230 activities were closely related to the changes of Fe³⁺and Fe²⁺in intracellular and extracellular concentrations.The main reason was that the presence of Fe³⁺could act as an active center of the enzyme to increase the activity of the enzyme,thereby.Thereby,the degradation of pyrene has been efficiency improved.(7)Further speculate on the mechanism of iron ions in the process of degrading PAHs by Rhodococcus ruber L9:Fe³⁺receives electrons into Fe²⁺after it adding into the system and.Under the action of ATP,pyrene goes into the cell through specific proteins on the cell membrane,and induces DNA transcription corresponding mRNA is produced,and then a large number of enzyme proteins related to strontium degradation are produced and excreted;Fe³⁺forms an active center of C120,which makes the enzyme have strong activity,and the elevated of the concentration of Fe²⁺in the system also makes the activity of C230 increased,which accelerated the reaction rate;Fe²⁺was reconverted to Fe³⁺under the action of hydrolysis and oxidation;while the amount of increased enzyme and the increased activity of enzyme made the ring-opening cracking process of pyrene more faster.