Three-Dimensional Motions And Adhesion Of Bacteria On Dynamic Surfaces

Marine antifouling is still a challenging problem today.Dynamic surface that continuously undergo physical changes or chemical reactions provides a promising way to inhibit marine biofouling.However,the antifouling mechanism at the molecular level remains unclear.In this thesis,we have prepared dynamic surfaces which can undergo deformation with the surface stiffness and wettability.We carefully investigated the three-dimensional（3D）motions of Escherichia coli（E.coli）,Pseudonomas.sp nov 776 and Pseudomonas aeruginosa（PAO1）on the surfaces by using a home-made digital holographic microscope（DHM）.With the help of RNA sequencing experiments,we attempt to insight into the antifouling mechanism of the dynamic surfaces.The main contents of the thesis are as follows:（1）Polydimethylsiloxane（PDMS）surfaces with different stiffness were prepared.The3D motions and adhesion of E.coli and Pseudonomas.sp on the surfaces were examined in real-time by DHM.The adhered bacteria significantly decrease as the surface becomes softer.This is because the softer surface is more dynamic or its physical deformation is more frequent,and the bacteria are difficult to land,grow or multiply on the surface.On the other hand,as the surface stiffness decreases,the bacteria have more frequent adaptive behaviors including the tumble motions for E.coli and flick motions for Pseudomonas sp.,which further reduces the bacterial adhesion.In contrast to a non-tumbling mutant（HCB1414）,E.coli can reduce the bacterial adhesion by 60%due to the adaptive responses.RNA-sequencing experiments show the significant downregulation of Cph2 and Csr A as well as upregulation of Gcv A,further indicating the adaptive responses can promote bacterial motility and prevent the bacterial adhesion.（2）PDMS-based slipery surface was prepared by infusing n-alkanes.The 3D motions of Pseudomonas aeruginosa on such a dynamic surface were observed in real-time by DHM.The slippery surface can effectively inhibit the adhesion of bacteria.As the surface sliding angle decreases,the adhesion number of PAO1 decreases.The analysis of the 3D behaviors of PAO1 demonstrates that the ratio of subdiffusive population(N_sub)to active one(N_active)decreases as the surface sliding angle decreases,indicating that less bacteria subdiffusively swim,thus avoiding the bacterial adhesion.In addition,the bacteria have more circular motions on more slippery surfaces,suggesting that the slippery surface can change the motion modes of the nearby bacteria.With 3D real-time tracking of DHM,we are able to monitor the behaviors of bacteria on dynamic surfaces,especially how they move in the direction perpendicular to the surface,which is closely related to surface adhesion.Our study reveals that the physical deformation of dynamic surface can give rise to significant adaptive responses of bacteria,which change their motion mode and adhesion.This point makes significance for design of antifouling materials.