Department of Chemical Engineering, Stanford University, Stanford, California 94305-5025.
Appl Environ Microbiol. 1991 Jan;57(1):102-13. doi: 10.1128/aem.57.1.102-113.1991.
A dense aggregate of cells was retained in a reactor by a supported porous membrane. A continuous flow of nutrient medium was maintained through the cell aggregate and membrane. The hydraulic resistance of the cell aggregate was monitored throughout experiments with either growing or chemically cross-linked cells, under conditions of varying flow rates. Digital image analysis was used to characterize the sizes, separations, and orientations of several thousand individual cells in electron micrographs of chemically cross-linked cell aggregates. Two nonlinear phenomena were observed. First, the hydraulic resistance varied in direct relation to and reversibly with flow rate. Second, in constant flow-rate experiments the hydraulic resistance increased with time at a faster rate than could be attributed to cell growth. Both of these phenomena were dependent upon and could be explained by the ability of cells to move with respect to one another, under the influences of Brownian motion and of convection. Such relative motion could allow changes in net alignment of cells in the direction of flow and in the volume fraction of cells in the aggregate. This explanation is consistent with image analysis data. The observed sensitivity of hydraulic resistance to flow rate was inconsistent with a model that assumed elastic deformation of individual cells, and no evidence of cell deformation was found in electron micrographs.
细胞致密聚集体被多孔支撑膜保留在反应器中。通过细胞聚集体和膜持续保持营养培养基的连续流动。在生长或化学交联细胞的实验中，监测细胞聚集体的水力阻力，在不同流速条件下。数字图像分析用于在化学交联细胞聚集体的电子显微镜照片中表征几千个单个细胞的大小、分离和取向。观察到两个非线性现象。首先，水力阻力与流速直接相关并呈可逆关系。其次，在恒定流速实验中，水力阻力随时间的增加而以比归因于细胞生长更快的速率增加。这两种现象都取决于细胞在布朗运动和对流的影响下彼此相对移动的能力，并且可以通过这种相对运动来解释。这种相对运动可以允许细胞在流动方向上的净对准和聚集体中细胞的体积分数发生变化。该解释与图像分析数据一致。观察到的水力阻力对流速的敏感性与假设单个细胞弹性变形的模型不一致，并且在电子显微镜照片中未发现细胞变形的证据。
