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Identify the four phases of the growth curve Calculate generation time Make use of the growth curve OBJECTIVES

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Growth an orderly increase in cell number cell division （细胞分裂） a developmental program superimposed upon this increase cell differentiation （细胞分化）

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Binary Fission 2 0, 2 1, 2 2, 2 3, 2 4, 2 5, 2 6 …… 1, 2, 4, 8, 16, 32, 64…… Parent cell Daughter cell

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一条典型的生长曲线至少可以分为迟缓期， 对数期，稳定期和衰亡期等四个生长时期。

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Lag phase making new enzymes in response to new medium

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Log phase exponential growth – Desired for production of products – Most sensitive to environment

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Stationary phase – nutrients becoming limiting or waste products becoming toxic – secondary metabolism – death rate = division rate

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Death phase death exceeds division

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N1N1 N2N2 t

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The generation time of a culture is defined as A. the time it takes a cell to divide. B. the time it takes the culture to begin growth. C. the interval of time between the end of log phase to the stationary phase of growth. D. the period of time it took for the organism to appear on earth. E. how long the culture has been growing. 世代时间

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BacteriumMedium Generation Time (minutes) Escherichia coliGlucose-salts17 Bacillus megateriumSucrose-salts25 Streptococcus lactisMilk26 Streptococcus lactisLactose broth48 Staphylococcus aureusHeart infusion broth27-30 Lactobacillus acidophilusMilk66-87 Rhizobium japonicumMannitol-salts-yeast extract Mycobacterium tuberculosisSynthetic Treponema pallidumRabbit testes1980

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Calculation of Generation Time G = t/n G ---generation time (time for the cells to divide) t---time (interval in hours or minutes) n---number of generations (number of times the cell population doubles during the time interval)

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Solve for n log N 2 = log N 1 + nlog2 n = log N 2 - log N 1 log2 n = log N 2 - log N n = 3.3 log N 2 / N 1 N 1 = number of bacteria at the beginning of a time interval N 2 = number of bacteria at the end of the time interval N 2 = N 1 × 2 n (This equation is an expression of growth by binary fission) Solve for G G = t/n G = t 3.3 log N2/ N1

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A bacterium with a generation time of 0.5 hours will grow from a population of 10 3 to 10 9 cells, in about how many hours? A. 25 B. 3 C. 40 D. 20 E. 10 Solve for G G = t / n G = t 3.3 log N2/ N1

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Bacteria from_______ phase can served as “seed” to another culture medium effectively, to decrease the lag phase Bacteria from_______ phase have the most typical morph － ological, biochemical and physiological features Bacteria from_______ phase can be used to screen medicine Use of the Growth curve

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If at time 0 you had 10 million cells and two hours later had 40 million cells, what is the generation time? generation time

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