| Polycyclic aromatic hydrocarbons(PAHs)are ubiquitous persistent organic pollutions which are resistant to environmental degradation.PAHs can pose acute or chronic toxic effect on the environment and human being.More and more researchers have paid attentions on the pollution because some of them have been even identified as carcinogenic,mutagenic and teratogenic.Although PAHs may be reduced by adsorption,volatilization,photolysis,and chemical degradation,biodegradation is the main degradation process due to the characteristics of low cost and non-secondary pollution.However,the coexisting heavy metals in the environment may affect the degradation of PAHs by impacting the growth of microorganism,enzyme productions and characteristics of enzymatic degradation process of PAHs bidegradation.In this research,phenthrene(PHE),Pb(?)and Cd(?)were selected as typical and ubiquitous models of PAHs and heavy metals,respectively.The mechanisms of the impact of Pb(?)and Cd(?)on the PIIE biodegradation by Bacillus sp.PI were elucidated by investigating the biodegradation rate,metabolites and enzyme variations(enzymatic degradation ability,component,and activities).The results were listed as follows:(1)Pb(?)and Cd(?)can affect the biodegradation of PHE,Cd(?)was much more toxic to Bacillus sp.P1 than Pb(?).In the first two days,the effect of Pb(?)and Cd(?)on PHE degradation were much greater than that in the last four days,degradation rate increased from 67.87%to 85.68%,and from 66.52%to 73.93%,respectively.The degradation rate then rose to 95.05%and 88.82%on day 6 by the effect of Pb(?)and Cd(?).The degradation rate of control group(without heavy metals)increased from 48.12%to 95.08%in six days.The results indicated that Bacillus sp.P1 was efficient bacteria on PHE degradation,heavy metals suppressed the biodegradation of PHE,and the inhibition effect was diminished with the extension of time.(2)PHE was degraded by Bacillus sp.P1 through protocatechuate pathway.Pb(?)and Cd(?)did not affect the metabolic pathways,they only had an effect on the concentration of degradation components.The inhibition effect of Cd(?)were stronger than Pb(?)on PHE metabolism,which can be attributed to that the toxicity of Cd(?)on microorganisms are greater than Pb(?).(3)The alterations of extracellular enzymes(EE)and intracellular enzymes(IE)concentrations were perceived through analyzing SDS-PAGE fingerprint by Gelpro software.With the increase of Pb(II)from 0 to 50 mg/L,the total contents(absolute integrated optical density)of EE and IE increased from 5.79×105 to 6.44×105,and from 7.19×105 to 7.54×105,respectively.Then declined from 4.24×105 to 4.21 ×105,and from 7.11×105 to 5.27×105 respectively with the increase of Pb(?)from 100 to 150 mg/L.The protein bands with molecular mass of 33-45 kDa of EE(IE)increased from 8.61×104 to 1.31 ×105(from 1.69×105 to 2.50×105),then decreased from 8.26×104 to 7.18×105(from 1.42×105 to 1.19×105).With the increase of Cd(?)from 0 to 300 mg/L,the total contents of EE and IE decreased from 8.37×106 to 5.49×106,and from 1.54×107 to 6.01×106,respectively.The protein bands with molecular mass of 33-45 kDa of EE(IE)decreased from 4.31×105 to 2.39×105,5.66×106 to 4.78×104,respectively.Meanwhile,the protein bands with small molecular weight of EE were almost lost under relatively higher exposure of Cb(?).(4)Catechol 2,3-dioxygenase activities in EE and IE were remarkably changed in the presence of different concentrations of Pb(?)during the process of degrading PHE.The activities of EE and IE increased from 274.61 to 296.15 U/mg,and from 890.09 to 1003.30 U/mg as the increasing of Pb(?)from 0 to 50 mg/L,then decreased from 244.04 to 99.27 U/mg,and from 784.93 to 304.55 U/mg as the increasing of Pb(?)from 100 to 300 mg/L.Cd(?)showed an inhibition effect on catechol 2,3-dioxygenase activities in EE and IE.The activities decreased from 266.96 to 38.93 U/mg,and from 886.30 to 290.26 U/mg,respectively as the increasing of Cd(?)from 0 to 300 mg/L.(5)Low concentrations of Pb(?)can increase the enzymatic degradation of PHE at an optimal pH and temperature,while high Pb(?)can decrease the enzymatic degradation.PHE degradation by extracellular enzymes and intracellular enzymes increased from 68.40%to 74.67%,and from 85.21%to 87.03%as the increasing of Pb(?)from 0 to 50 mg/L,then decreased to 63.93%80.56%as the increasing of Pb(?)to 300 mg/L,respectively.Cd(?)posed an inhibition effect on PHE degradation by EE and IE,the degradation decreased from 79.86%to 64.59%,and from 87.96%to 74.83%,respectively as the increasing of Cd(?)from 0 to 300 mg/L.The results collectively proved that Pb(?)and Cd(?)can affect the degrading ability of Bacillus sp.P1 by impacting the content,the component and activities of enzymes during PHE degradation process. |
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