chapter_6 - Growth increase in cellular constituents that...

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1 1 Chapter 6 Microbial Growth 2 Growth increase in cellular constituents that may result in: increase in cell number e.g., when microorganisms reproduce by budding or binary fission increase in cell size e.g., coenocytic microorganisms have nuclear divisions that are not accompanied by cell divisions microbiologists usually study population growth rather than growth of individual cells Day 1 = 1 cent What would you do? Day 7 = 16 cents Day 14 = $82 Day 21 = $10,496 Day 30 = $5,368,709 Day 31 = $10,737,418 4 The Growth Curve observed when microorganisms are cultivated in batch culture culture incubated in a closed vessel with a single batch of medium usually plotted as logarithm of cell number versus time usually has four distinct phases
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2 5 Figure 6.1 no increase maximal rate of division and population growth population growth ceases decline in population size 6 Lag Phase cell synthesizing new components e.g., to replenish spent materials e.g., to adapt to new medium or other conditions varies in length in some cases can be very short or even absent 7 Exponential Phase also called log phase rate of growth is constant population is most uniform in terms of chemical and physical properties during this phase 8 cells are dividing and doubling in number at regular intervals
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3 9 Figure 6.3 each individual cell divides at a slightly different time curve rises smoothly rather than as discrete steps 10 Balanced growth during log phase, cells exhibit balanced growth cellular constituents manufactured at constant rates relative to each other 11 Unbalanced growth rates of synthesis of cell components vary relative to each other occurs under a variety of conditions change in nutrient levels shift-up (poor medium to rich medium) shift-down (rich medium to poor medium) change in environmental conditions 12 Stationary Phase total number of viable cells remains constant may occur because metabolically active cells stop reproducing may occur because reproductive rate is balanced by death rate
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4 13 Possible reasons for entry into stationary phase nutrient limitation limited oxygen availability toxic waste accumulation critical population density reached 14 Starvation responses morphological changes e.g., endospore formation decrease in size, protoplast shrinkage, and nucleoid condensation production of starvation proteins long-term survival increased virulence
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chapter_6 - Growth increase in cellular constituents that...

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