第六章微生物的生长及其控制z95rcr.ppt

* When a fresh medium is inoculated with a given number of cells, and the population growth is monitored over a period of time, plotting the data will yield a typical bacterial growth curve (Figure 3 ). Figure 3. The typical bacterial growth curve. When bacteria are grown in a closed system (also called a batch culture), like a test tube, the population of cells almost always exhibits these growth dynamics:? cells initially adjust to the new medium (lag phase) until they can start dividing regularly by the process of binary fission (exponential phase).? When their growth becomes limited, the cells stop dividing (stationary phase), until eventually they show loss of viability (death phase).? Note the parameters of the x and y axes.? Growth is expressed as change in the number viable cells vs time.? Generation times are calculated during the exponential phase of growth.? Time measurements are in hours for bacteria with short generation times. * 将少量单细胞的纯培养，接种到一恒定容积的液体培养基中，在适宜条件下培养，定时取样，测菌量。以培养时间为横坐标，以细菌增长数目的对数为纵坐标，绘制所得的曲线。 典型的生长曲线一般可分为延迟期、对数期、稳定期和衰亡期。 a. Lag Phase Organisms are adjusting to the environment ( little or no division). They are synthesizing DNA, ribosomes and enzymes to breakdown nutrients, and to be used for growth. b. Log or Logarithmic phase Division is at a constant rate (generation time) but varies with species, temperature and media. Cells are most susceptible to inhibitors. c. Stationary phase Dying and dividing organisms are at an equilibrium. Death is due to reduced nutrients, pH changes, toxic waste and reduced oxygen. Cells are smaller and have fewer ribosomes. In some cases cells do not die but they are not multiplying. d. Death or Decline phase The population is dying in a geometric fashion so there are more deaths than new cells. Deaths are due to the factors in stationary phase in addition to lytic enzymes that are released when bacteria lyse. 以时间为横坐标，样品中活菌数的对数为纵坐标做曲线，它反映了细菌群体的数量随时间变化的情况，即生长情况，称为生长曲线。 ★它是将少量的已知浓度的纯菌种接种到一定体积的液体培养基中，在适