Regulation And Mechanism Of Tween80-Saponin On Transmembrane Transmission Of PAHs

Polycyclic Aromatic Hydrocarbons(PAHs)are one of the main pollutants in soil environment.Bacterial remediation of PAHs contaminated soil has been suggested as one of effective remediation methods due to the advantages of low cost,simple operation and low ecological risks.However,the low bioavailability of PAHs in soil generally limited its remediation performance.Therefore,how to effectively improve the bioavailability of PAHs by employing surfactants,has been one of the hotspots in current soil pollution research.The removal of PAHs by soil bacteria mainly involves the surface behaviors such as bacterial surface adsorption,transmembrane transport and intracellular degradation.Among them,transmembrane transport is the key to limit the degradation rate.However,the effect and mechanism of surfactant on transmembrane transport of PAHs is unclear.In this study,the effects of surfactant on bacterial adsorption,transmembrane transport,degradation of PAHs and other interface processes were studied,by using Tween 80-saponin and alikes surfactant representative,and Pseudomonas aeruginosa as a representative of degradation bacteria,in order to shed some lights on surfactant-enhanced bacteria remediation of PAHs contaminated soil.The main results are summarized as follows:(1)It was found that Tween 80 could promote the degradation of phenanthrene by R aeruginosa^but inhibit the adsorption of phenanthrene.During the culture period(0-6 days),the apparent removal rate and degradation rate of phenanthrene increased gradually,while the adsorption rate increased first and then decreased.When 8 CMC Tween 80 was applied,the adsorption rate reached the maximum on the third day up to 23.07%.The apparent removal rate and degradation rate on the sixth day can reach 68.82%and 66.87%,respectively.The inhibitory effect of surfactant on the adsorption of phenanthrene by bacteria could be attributed to its reduction of Cell Surface Hydrophobicity(CSH).For example,8 CMC Tween 80 could decrease the CSH of bacteria by 77.94%.(2)It was found that the surfactant could change the membrane permeability of P.aeruginosa,which was conducive to the transport of pollutants.The Outer Membrane Permeability(OMP)of bacteria increased with the concentration of 8 kinds of surfactant studied.The larger the alkyl chain length of Tween series,the stronger the OMP promotion.For example,Tween 20,Tween 40 and Tween 80 of 1 CMC,the promotion of OMP was increased by 0.62,0.67,and 2 times,respectively.The promotion of OMP by Tween 80-saponin increased with the decrease of the proportion of saponin.For example,2 CMC was 2.71(10:0),2.71(9:1),2.51(5:5),2.44(1:9),and 2.44(0:10)times more than the blank control(surfactant-free).Low concentration(0-1 CMC)surfactant could significantly increase intracellular membrane permeability(Inner Membrane Permeability,IMP).With 1 CMC Tween series,such as 1.33(Tween 20),1.3(Tween 40),1.07(Tween 80)times more than the blank control.The Tween series and TritonX-100 could significantly increase the tryptophan content on the bacterial surface,while high concentration of Tween 80-saponin showed slight inhibition effect.(3)Liposomes can better simulate the transmembrane diffusion of PAHs,and it was found that surfactant can significantly enhance the transmembrane diffusivity of PAHs.The diffusivity of PAHs in liposomes was proportional to the logKow of PAHs and inversely proportional to the temperature of the system.For example,the diffusivity of liposome-encapsulated PAHs at 4 h diffusion equilibrium:pyrene(80.50%)>phenanthrene(30.21%)>acenaphthene(29.07%)>naphthalene(20.50%).At 8 CMC Tween 80,the diffusivity of phenanthrene:15?(80.79%)>20?(71.47%)>25?(66.29%)>30?(57.46%)>35?(45.19%).The diffusion rate of liposome-coated phenanthrene increased with the increase of surfactant concentration,and was inversely proportional to the alkyl chain length.The ratio of saponin could promote the diffusion of phenanthrene.For example,the difffusivity of the surfactant phenanthrene liposome was:10:0(66.29%)<9:1(74.61%)<5:5(77.34%)<1:9(83.33%)<0:10(84.76%)of Tween80-saponin at 8 CMC,respectively.