MICRB 265 (10/21/13) Microbial Nutrition and Growth (con't)

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University of Alberta
Microbiology (Biological Sciences)
Brian Lanoil

MICRB 254 (October 21, 2013) Microbial Nutrition and Growth (con’t) Chemostat: Continuous Culture • Fresh medium input and microbe-containing effluent output • Very different from batch culture in that the cells are ALWAYS in growth phase • NOTE: o Dilution rate = growth rate = flow rate • Growth yield is equal to the cell count o The growth yield can continue increasing even though the growth rate is the same • Start with very low concentration of nutrients o Increasing nutrient concentration makes the culture reach a point where their growth is not affected by limitations in nutrients (cells cannot grown any faster than that) • This method is good for growing cells at a constant and known rate • Cell crowding is not a problem  cell cultures can eventually reach a consistency of toothpaste (10^12 cells/mL) o A typical culture (cloudy and broth-like thickness) has cell concentration of 10^9 o Natural culture from say, a lake, will have a cell concentration of around 10^6. • Low dilution = cell starvation • High dilution = washout of cells o Cells cannot keep up with the input of nutrients and get flushed out Applications of the Chemostat • Industrial production o Ex. Antibiotics  Minimum cell yield to maximize product • Wastewater treatment o To lower rate of discharge • Continuous growth and harvesting cells o Cells are growing at a stead state of exponential growth Environmental Effects on Microbial Growth • Extremophile grow under conditions that would be harsh for humans (conditions that would kill most other organisms) o Most extremophiles are prokaryotes o Keep in mind that even though they can grow in extreme conditions, the range at which they can survive is not any greater than those of other organisms  Our “normal” is their “extreme”  Their “normal” is out “extreme” • Different environmental factors o Temperature  -36 to 113 degrees celcius o pH  0 to 11.5 o Osmotic effects  Pure water to 30% NaCl water o Presence/absence of oxygen o Pressure  Barophiles live at high pressures o Radiation Effect of
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