Lecture 151. Recall the equation governing bacterial growth a. N=N0 x 2nb. N- N0 x 2vt2. Explain why the progression of bacterial growth looks linear on a semi-log plot a. One axis is linear (usually time)b. One axis is logarithmic (# of cells)3. Calculate the generation time or the number of generations per hour of a culture based on a given plot a. Find coordinate of population that doubles then find time points g = t/n, g =1/v and v = 1/g4. Describe what happens in the four growth phases of batch cultures a. Lag Phasei. Metabolic adjustment, may take longer is cells were in death stage shorter in complex media, longer in minimum ii. Takes longer if transferred from complex to defined media.iii. Nutrient shift down enzymes made to synthesize essential metabolites before growth beginsiv. Viable count below ODb. Exponentiali. Cells and mass double in each generationii. Uniform population ideal for biochemical and physiological studiesiii. Longer in minimum, short in complex. Complex only need a transporter to absorb nutrients and minimal must synthesize.iv. Rates vary on species and environment.v. Microbial growth under PRECISE control Viable count below ODc. Stationaryi. Cell growth = cell death or cells stop dividing but are metabolically active cause by depletion of nutrients/ and or build up of waste viable count above ODii. Physiological adjustments “starvation survival”d. Death Phasei. Cells dying greater than cell divisionii. Depleted nutrients and toxic waste cause OD more than viable count because dead cells contribute to OD iii. Death is exponential vary by species.iv. Surviving cells grow in new media, long lag phase if unhealthy 5. Explain what parameters determine the presence and duration of the lag phasea. What medium it came from6. Explain what parameters control the growth rate in exponential phase a. What kind of medium is in them7. Explain parameters that can cause the stationary phase a. Consumed most of nutrient. Starting to accumulate waste8. Compare and contrast the viable count and turbidity curves in the four phases a. Viable count:i. Lag: no growthii. Exponential: exponential growth creeping up with turbidityiii. Stationary: Plateaus iv. Death: starts decreasing but not to zerob. Turbidity i. Lag: Little growthii. Exponential: exponential growth high than viable iii. Stationary: levels out lower than viableiv. Death: Only decreases slightly 9. Explain Liebig’s law of the minimum a. Limiting nutrient concentration affects growth rate and yieldb. Low: affects bothc. High: Affects yield but not rate10. Explain how growth factor bioassays work a. Determine the concentration of a given nutrient (vitamin) on growth rate of yield on a fastidious organism in media with vitamin as sole source of foodand other essential nutrients in excess. Organisms cannot synthesize vitamin, so vitamin must be present for organisms to grow. Growth response proportional to vitamin concentrationb. Examplei. Lactibacillus fermentation bioassay of thiamine and histidine. Both must be present for growth. If histidine is limiting nutrient growth willcontinue until thiamine runs out11. Recall the key points describing bacterial growth in chemostats a. Flow in and out constant pH, volume, aeration growth rate = dilution rate, dilution rate = flow rate/ chemostat volume 12. Explain how cell density is controlled by flow rate and limiting nutrient concentration a. At steady state bacterial concentration remains constant up until very fast flow rate, when growth cannot keep up with dilution. Cells “wash out” out chemostat.b. Limiting nutrient concentration remains low and constant until right before wash out, where it rises up to equal concentration in fresh medium (is notlonger used)13. Explain why the bacterial concentration remains constant in the steady state region of chemostat function a. Doubling time decreases as dilution rate increases (more limiting nutrient is available)b. Doubling time and dilution vary, but bacterial contant 14. Explain why the cell output increases while the bacterial concentration remains constant in the steady state region of chemostat function a. Total number of cells (g/L/hr) increase until washout then decreases to zero cell growth makes up for cells washed out during steady state, nutrients also
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