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Microbial Growth

Microbial Growth. What do they need to grow?. Physical needs Temperature, proper pH, etc. Chemical needs Molecules for food, ATP production, coenzymes, etc. Growth = increase in number , not size Binary fission, some by budding E coli growing Generation time: doubling time

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Microbial Growth

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  1. Microbial Growth

  2. What do they need to grow? • Physical needs • Temperature, proper pH, etc. • Chemical needs • Molecules for food, ATP production, coenzymes, etc. • Growth = increase in number, not size • Binary fission, some by budding • E coli growing • Generation time: doubling time • 1-2 hrs for most bacteria • E. coli can divide in 20 minutes in optimum conditions!

  3. Graph shows a closed system Lag phase Cells acclimating Preparing to divide Log phase Exponential growth Generation time reaches constant minimum Must susceptible to adverse conditions Heat, radiation, drugs Total growth = # of cells X 2n (n = number of generations) Stationary phase # dividing = # dying Population stabilizes Decrease in nutrients, increase in wastes Death phase # deaths > # new cells What is the bacterial growth curve?

  4. How can I measure bacterial growth directly? • Direct count • Plate counts • Serial dilutions • Then either pour plates or spread plates • Pro: only measures viable cells • Con: time consuming!

  5. Pro: only measures viable cells • Con: time consuming!

  6. How can I measure bacterial growth directly? • Direct microscopic count • Use gridded slide to count • Pro: no incubation time • Con: counts dead cells, too; hard to count moving bacteria • Take average and calculate back from dilution • Coulter counter

  7. How can I measure bacterial growth indirectly? • Turbidity • Cloudiness and more bacteria present • Use spectrophotometer • Percentage of transmission • Only works if you have at least a 1M cells per milliliter

  8. What are the physical requirements for growth? • Temperature • Each species has preferred temp range (over about 30 degrees C spread) • Dies quickly outside range • Minimum growth temp • Maximum growth temp • Optimum growth temp • Usually near top of range (close to max)

  9. What are the physical requirements for growth? • Temperature: Three groups • Psychrophiles (cold loving): 5-20 degrees C • Psychrotrophs: 20-30 degrees C • Contribute to food spoilage in refrigerator • Mesophiles (mod.-temp): 25-40 degrees C • Most common • Often in animals • Thermophiles (hot): 45-60 degrees C • Obligate thermophiles: only above 50 degrees C • Extreme thermophiles: above 80 degrees C • Archaea

  10. What are the physical requirements for growth? • pH • Most bacteria prefer 6.5-7.5 • When growing, pH changes • Additive to growth medium buffer pH • Phosphate salts, amino acids • Yeast, molds more tolerant of greater range • Optimum 5-6 • Acidophiles • Not many

  11. What are the physical requirements for growth? • Osmotic pressure • Bacteria are 80% to 90% water • Hypertonic solutions ________ water ____ cell • Results in plasmolysis • PM pulls away from cell wall • Retards bacterial growth • Why meat, butter, etc. salted • Extreme halophiles • Obligate halophiles • Bacteria in Dead Sea, 30% salt • Facultative halophiles • Can grow in up to 2% salt • Some in up to 15% • Salt not required for growth

  12. Anaerobic Culture Methods • Reducing media • Anaerobic jar • Contain chemicals (thioglycollate or oxyrase) that combine O2 • Heated to drive off O2

  13. What are all the different “troph” types? Energy source: nonliving environment • Photoautotroph • Chemoautotroph Energy source: other organisms or sunlight • Photoheterotroph • Chemoheterotroph • Saprobe • Parasite

  14. What are the chemical requirements for growth? • Oxygen • Aerobe • Obligate aerobe • Anaerobe • Obligate anaerobe • Often harmed by oxygen • Clostriudium • Facultative anaerobe • Uses O2 when present • Can use anaerobic path or fermentation • E. coli • Aerotolerant anaerobes • Tolerate oxygen but don’t use it • Lactobacilli for cheese, pickles • Microaerophiles • Require oxygen at low concentration • Others include nitrogen, sulfur, phosphorus, etc.

  15. What are symbiotic relationships? • Mutualism • lichen • Commensalism • Satellitism • Microbial flora • Lactobacillus • E. coli • Parasitism

  16. What are non-symbiotic relationships? • Synergism • Roots & bacteria • Antagonism • Penicillium Photo from: http://scientificteaching.wisc.edu/products/PeanutFiles/imagesforsite/penicillium.jpg

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