Adsorption Of Competence-Stimulating Factor On Soil Minerals And Influence On The Quorum Sensing In Pseudomonas Aeruginosa

Quorum sensing is a communication mechanism for bacteria to regulate a variety of physiological behaviors,among which signal molecules are important mediators.The interaction of minerals with bacteria and signal molecules profoundly affects many quorum sensing regulated soil biochemical processes,such as the natural transformation,the virulence expression of pathogenic bacteria,and the formation of biofilms.This study used Competence-stimulating factor(CSF),Pseudomonas aeruginosa PAO1,goethite,montmorillonite,kaolinite,birnessite and hematite(15,75,462 nm)as the material.Traditional chemical and microbiological methods combined with isothermal titration calorimetry(ITC),fourier transform infrared spectrometer(FTIR),X-ray photoelectron spectrometer(XPS),synchrotron radiation-based fourier transform infrared(SR-FTIR),liquid chromatography-mass spectrometry(HPLC-MS/MS)were employed to understand the binding mechanism of CSF on soil minerals,the effect of birnessite and hematite on quorum sensing in P.aeruginosa.The main results are as below:(1)We clarified that the binding mechanism of CSF on montmorillonite,kaolinite and goethite was via electrostatic interaction.The adsorption of CSF on minerals could well fit the Freundlich equation,and the adsorption of CSF on the surface of montmorillonite could reach 15 mg/kg,which was significantly higher than the adsorption of CSF on goethite and kaolinite.The binding constant(K_F)between CSF and montmorillonite was 1.6-2.5 times that of kaolinite,1.7-10.8 times that of goethite,while the enthalpy change(?H)was 4.5-8.2 times that of kaolinite and 3.3-5.9 times that of goethite.This result indicating that the adsorption affinity of montmorillonite on CSF was higher than that of kaolinite and goethite.(2)We proved the inhibition of birnessite on virulence expression regulated by quorum sensing in P.aeruginosa PAO1.This might be due to that birnessite increased the content of reactive oxygen species(ROS)in PAO1 cells and reduced the synthesis of signal molecules;besides,birnessite significantly down-regulated the expression of PAO1signaling molecule receptor genes,therefore resulting in a reduction in the virulence expression of PAO1 by 29.2%-41.7%,meanwhile,these inhibitory effects were weakened under light condition.(3)We demonstrated the size-dependent effect of hematite on virulence expression regulated by quorum sensing in P.aeruginosa PAO1.The growth of PAO1 increased as the size of hematite decreases from 462 nm to 15 nm.However,the virulence(pyocyanin,elastase,etc.)expression of PAO1 decreased as the size of hematite decreases from 462 nm to 15 nm.This result was because that hematite absorbed signal molecules and induced PAO1 to produce reactive oxygen species(ROS),resulting in a decrease in the content of extracellular signal molecules;in addition,hematite inhibited the expression of receptor genes by secreting Fe³⁺and entering into PAO1 cells to bind with signal receptor proteins,thereby affecting the virulence expression of PAO1.