Lect3-KR

# Lect3-KR - Microbial Growth PMB/MCB112 September 1 2010...

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Microbial Growth PMB/MCB112 September 1, 2010

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time When a bacterial population has sufficient nutrients, it can undergo exponential growth . The number of cells in the population and the total cell mass increase by a factor of 2 during each generation time . 0 1 2 3

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0 2 4 6 8 10 0 50 100 150 200 250 number of cells time Equations describing exponential growth N = N 0 x 2 n where N 0 = initial cell number N = final cell number n = number of generations generation time or doubling time g = t/n where t = time elapsed during exponential growth

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Typical lab calculation about cell growth: For an experiment tomorrow, I need 500 ml of Caulobacter at a density of 8 x 10 8 cells/ml. I need to start the experiment 15 hours from now, and I know that the doubling time of Caulobacter in this medium is 1.5 hours. How much of my stock culture (10 9 cells/ml) do I use to inoculate the 500 ml flask? N = N 0 x 2 n N = 8 x 10 8 cells/ml x 500 ml = 4 x 10 11 cells n = t/g =15 h / 1.5 h = 10 generations Therefore N 0 = 3.9 x 10 8 cells 3.9 x 10 8 cells / 10 9 cells/ml = .39 ml of stock culture

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Growth phases in batch culture
Stationary Phase Conditions change so that microbial growth is limited: run out of an essential nutrient accumulate a toxic waste product No net increase or decrease in cell number (either not dividing, or divisions = deaths) Energy metabolism and some biosynthetic processes can continue At the molecular level, stationary phase is not a single physiological state (cells starved for C ≠ cells starved for P ≠ cells that have accumulated high levels of lactic acid) σ S controls response to many stresses, giving cross-protection

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Lag Phase Occurs (A) when a stationary culture is diluted into fresh medium or (B) when cells are transferred from rich to minimal medium Bacteria must sense new environment and synthesize either A) many proteins needed for rapid growth, which were not produced during starvation, or B) specific proteins needed to produce the nutrients not already present in the culture medium
Chemostat an open system for continuous microbial culture

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Effects of increasing nutrient concentration in a chemostat
Relationship between dilution rate and growth rate in a chemostat

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Culture media Rich/complex medium
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Lect3-KR - Microbial Growth PMB/MCB112 September 1 2010...

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