Nonspecific and Specific Adhesion of Bacterial Cells to Membranes

这项建议涉及研究细菌细胞与膜的粘附性，这些膜用于各种工业规模的分离技术，如反渗透和海水淡化。细胞与膜表面的粘合是一个分两步进行的过程。首先，膜表面附近的细胞被范德华引力、静电引力等远程胶体力固定，以及氢键等短程相互作用。一旦被固定，细胞就开始投射结构并合成细胞外聚合物分子，这些分子弥合了细胞和膜之间的缝隙，并牢固地将细胞附着在表面。实验将在一个平行的平板流室中进行，该流室安装在配备了视频显微镜和敏感光的相差显微镜的工作台上通过光电倍增管进行强度测量。腔室的底板是一块玻璃滑板，上面浇注着薄的聚合物薄膜。膜将由不同的聚合物制成，如醋酸纤维素和聚甲基丙烯酸甲酯(PMMA)，这些聚合物将具有不同的表面电荷(通过Zeta电位测量来表征)和疏水性(通过接触角测量来表征)。将使用该电池进行两项实验。在第一种情况下，稀释的细胞悬浮液将缓慢地通过小室灌流，细胞将被允许以低密度吸收到聚合物膜支撑物上。细胞与膜之间的分离距离将由全内反射显微镜测量。在这种技术中，激光束以小角度入射到玻璃载玻片上，完全从玻璃表面反射，并产生一种垂直于玻璃表面传播并进入腔体的消逝波。电池对波的散射由光电倍增管检测，通过这种测量可以得到细胞与膜的分离距离。电池分离距离将作为聚合物膜表面电荷和疏水性的函数来测量，以及细菌细胞的电荷和疏水性。后者将与生长周期阶段相关。在第二组实验中，通过视频显微镜观察通过平行板室的流速变化时附着细胞的命运，来测量附着细胞的脱附率作为外加剪切率的函数。然后，分离特性将与分离距离相关，并最终与膜和电池的疏水性和表面电荷特性相关。

This proposal is concerned with studying the adhesion of bacterial cells to membranes which are used in a variety of industrial scale separations technologies such as reverse osmosis and desalination. The adhesion of a cell to a membrane surface is a two step process. First, cells in the vicinity of the membrane surface are immobilized by both long- range colloidal forces such as van der Waals attraction, electrostatic attraction, and short range interactions such as hydrogen bonding. Once immobilized, the cells begin to project structures and synthesize extracellular polymeric molecules which bridge the gap between the cells and the membrane, and firmly adhere the cell to the surface. Experiments will be undertaken in a parallel plate flow chamber which is mounted onto the stage of a phase contrast microscope equipped for videomicroscopy and sensitive light intensity measurement via a photomultiplier tube. The bottom plate of the chamber is a glass slide onto which thin polymeric membranes are cast. The membranes will be made of various polymers such as cellulose acetate and polymethyl methacrylate (PMMA), and these will have different surface charges (characterized by zeta potential measurements) and hydrophobicity (characterized by contact angle measurements). Two experiments will be undertaken using the cell. In the first, a dilute suspension of cells wills be slowly perfused through the chamber, and the cells will be allowed to absorb at low density onto the polymeric membrane support. The separation distance between the cell and the membrane will be measured by total internal reflection microscopy. In this technique a laser beam, impinging against the glass slide at a small angle of incidence, is totally reflected off of the glass surface and produces an evanescent wave which propagates normal to the surface and into the chamber. The scattering of the wave by the cell is detected by the photomultiplier tube, and the distance of separation of the cell from the membrane can be obtained from this measurement. The cell separation distance will be measured as a function of both the polymeric membrane surface charge and hydrophobicity, and the charge and hydrophobicity of the bacterial cell. The latter will be correlated with the growth cycle phase. In the second set of experiments, the detachment to attached cells will be measured as a function of applied shear rate by observing the fate of attached cells by video microscopy as the flow rate through the parallel plate chamber is varied. The detachment characteristics will then be correlated with the distance of separation, and ultimately to the hydrophobicity and surface charge characteristics of the membrane and cell.