•Identify the four phases of the growth curve

•Calculate generation time

•Make use of the growth curve

OBJECTIVES

Growth

• an orderly increase in cell numbercell division （细胞分裂）

• a developmental program superimposed upon this increasecell differentiation （细胞分化）

Binary Fission

20, 21, 22, 23, 24, 25, 26……

1, 2, 4, 8, 16, 32, 64……

Parent cell

Daughter cell

Daughter cell

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。

Lag phase

making new enzymes in response to new medium

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

Stationary phase – nutrients becoming limiting or waste products becoming toxic– secondary metabolism

– death rate = division rate

Death phase

death exceeds division

N1

N2

t

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

Bacterium MediumGeneration Time

(minutes)

Escherichia coli Glucose-salts 17

Bacillus  megaterium Sucrose-salts 25

Streptococcus lactis Milk 26

Streptococcus lactis Lactose broth 48

Staphylococcus aureus Heart infusion broth 27-30

Lactobacillus acidophilus Milk 66-87

Rhizobium japonicum Mannitol-salts-yeast extract 344-461

Mycobacterium tuberculosis Synthetic 792-932

Treponema pallidum Rabbit testes 1980

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)

Solve for nlog N2 = log N1 + nlog2 n = log N2 - log N1            log2 n = log N2 - log N1            0.301 n = 3.3 log N2/ N1

N1 = number of bacteria at the beginning of a time interval N2 = number of bacteria at the end of the time interval

N2 = N1 × 2n (This equation is an expression of growth by binary fission)

Solve for G G = t/n G =     t            3.3 log N2/ N1

A bacterium with a generation time of 0.5 hours will grow from a population of 103 to 109 cells, in about how many hours?

A. 25B. 3C. 40D. 20E. 10

Solve for G G = t / n G =       t                    3.3 log N2/ N1

•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

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