课件：微生物的生长与控制.ppt

* 获得同步生长的方法： 1. 机械法— 收集同样大小的细胞 密度梯度离心： 选择性滤膜法: 2. 调整生理条件法： 温度、光、限制因子等 例：温度开始很低，使其均处在 仅活着的状态——升高温度—— 同步生长 ３. 抑制ＤＮＡ生长法： 加入代谢抑制剂，阻遏DNA 复制——解阻遏——同步 * Synchronous Growth of Bacteria （参程皆能196页) Studying the growth of bacterial populations in batch or continuous cultures does not permit any conclusions about the growth behavior of individual cells, because the distribution of cell size (and hence cell age) among the members of the population is completely random. Information about the growth behavior of individual bacteria can, however, be obtained by the study of synchronous cultures. Synchronized cultures must be composed of cells which are all at the same stage of the bacterial cell cycle. Measurements made on synchronized cultures are equivalent to measurements made on individual cells. A number of clever techniques have been devised to obtain bacterial populations at the same stage in the cell cycle. Some techniques involve manipulation of environmental parameters which induces the population to start or stop growth at the same point in the cell cycle, while others are physical methods for selection of cells that have just completed the process of binary fission. Theoretically, the smallest cells in a bacterial population are those that have just completed the process of cell division.? Synchronous growth of a population of bacterial cells is illustrated in Figure 5.? Synchronous cultures rapidly lose synchrony because not all cells in the population divide at exactly the same size, age or time. * In the laboratory, under favorable conditions, a growing bacterial population doubles at regular intervals. Growth is by geometric progression: 1, 2, 4, 8, etc. or 20, 21, 22, 23.........2n (where n = the number of generations). This is called exponential growth.? In reality, exponential growth is only part of the bacterial life cycle, and not representative of the normal pattern of growth of bacteria in Nature. ★The ra