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**Microbial Growth**

**Microbial Growth**. Growth = an increase in the number of cells, not an increase in size Generation =growth by binary fission Generation time =time it takes for a cell to divide and the population to double. Bacteria divide by binary fission. Generation times vary for each organism.

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**Microbial Growth**

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  1. **Microbial Growth** • Growth= an increase in the number of cells, not an increase in size • Generation=growth by binary fission • Generation time=time it takes for a cell to divide and the population to double

  2. Bacteria divide by binary fission

  3. Generation times vary for each organism • E. coli • Mycobacterium tuberculosis

  4. **Bacterial growth curve**

  5. *Primary and Secondary metabolites I will ask you about secondary metabolites – know what they are, when they are produced and why.

  6. **Requirements for bacterial growth** • Environmental factors that influence • Temperature, pH, osmotic pressure, oxygen • Nutritional factors • Carbon, nitrogen, sulfur, and phosphorous • Trace elements

  7. *Optimum Growth Temperatures • Psychrophiles-optimum -5 to 15oC • Psychrotrophs- range from 20-30oC • Mesophiles- range from 25-45oC • Thermophiles-range from 45-70oC

  8. Growth rates in different temperatures

  9. pH influences the growth • Bacteria-prefer a pH range of 6.5-7.5 • Molds prefer a pH range of 5.0-6.0

  10. Osmotic environment influences growth

  11. **Oxygen preferences of organisms** • Obligate aerobes require oxygen for growth • Facultative anaerobes: can grow in aerobic or anaerobic environments • Obligate anaerobes: unable to grow in the presence of oxygen

  12. **Why can some organisms grow in the presence of oxygen?** • Because they have the ability to neutralize toxic oxygen molecules (superoxide, oxygen radicals) • Toxic forms of oxygen need to be neutralized by enzymes • Superoxide dismutase • Catalase

  13. *Oxygen Preferences of Bacteria

  14. Candle jars increase CO2 levels for growing capnophiles How does a candle jar create a CO2-enriched/O2-depleted environment? Is it an anaerobic environment?

  15. Anaerobic jars eliminate the oxygen for anaerobes to grow. How does the hydrogen gas generator create an anaerobic environment?

  16. Chemical requirements: Carbon • What are possible sources of carbon? • Bacteria are classified based on the source of carbon as either heterotrophs or autotrophs

  17. Classification based on Energy and Carbon sources

  18. Chemical Requirements: Nitrogen • Why do bacteria need nitrogen?

  19. Chemical requirements: Sulfur and Phosphorous • Why do bacteria need sulfur? • Why do bacteria need phosphorous?

  20. Chemical requirements: trace elements • Small amounts of minerals • Usually function as cofactors

  21. *Culture Media • Chemically defined • GSA A chemically defined medium is one where we know EXACTLY what the ingredients are. An undefined medium is one where we don’t know the exact chemical makeup (for instance, it may contain “protein digest”

  22. Chemically defined media

  23. Culture Media • Complex • Nutrient Agar • TSA • BHI

  24. *Culture Media • Selective • Differential • Selective and Differential

  25. *Ways to measure bacterial growth • Direct Count • Plate Count/Viable Cell Count • Measure Turbidity

  26. Direct Counts

  27. Plate counts require dilutions to obtain colonies

  28. Plate Counts: pour plate

  29. Plate Count-spread plate

  30. *Turbidity gives a rough estimate

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