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Microbial Growth

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Microbial Growth

  1. 1. Chapter 6: Microbial Growth August 15, 2013
  2. 2. Requirements for Growth • There are two ways to microbial growth can be divided • Physical • Chemical
  3. 3. Physical Requirements • Temperature • Hyperthermophiles –some members of Archaea, “extreme thermophiles” • Psychrophile-cold loving microbes • Mesophile-moderate temperatures (most common) • Thermophile-heat loving microbes • Psychrotrophs-capable of growing between 0 and 30 degrees Celsius (refrigerator temperatures)
  4. 4. • pH – the acidity or basicity of a solution • Most bacteria growth best at a pH between 6.5-7.5 • Neutral • Osmotic pressure • Microbes are 80-90% water • Adding solutes to solutions can reduce the presence of microbes (i.e. salt)
  5. 5. Chemical Requirements • Carbon • • Carbon is the structural backbone of all living matter Organic compounds • Nitrogen, Sulfur, Phosphorus • • N2 and P required for synthesis of DNA and ATP N2 required for protein synthesis • Trace Elements • • • Needed for enzymatic functions Can be added to media to culture microbes Fe, Cu, Zn
  6. 6. • Oxygen • Obligate Aerobes- require O2 to live • Facultative Anaerobes – can use O2 to live if present, but doesn’t require it for growth • Obligate Anaerobes – do NOT require O2 to live, harmed by it • Aerotolerant Aerobes- can not use O2 for growth, but they can handle it. Not necessarily harmed by the presence of O2
  7. 7. Chapter 6 Continued Microbial Growth
  8. 8. Page 166 in your Textbook
  9. 9. CULTURE MEDIA • There are many different mediums that microbes can grow in • Some require specific requirements, whereas others are more universal • Culture Medium: a nutrient material prepared for the growth of microorganisms in a laboratory
  10. 10. • To introduce microbes to a media, you have to inoculate them • This is what we did when we swabbed for microbes and put them on the agar. • If bacteria grows and multiplies on the media, it is referred to as a culture.
  11. 11. • A complex polysaccharide derived from a marine algae is called agar.
  12. 12. Types of Media • Chemically defined medium = the exact chemical composition is known • Complex media = a media that is made of nutrients, chemical composition varies from plate to plate; includes yeast, plant and meat extracts • Nutrient broth or nutrient agar • Reducing Media = anaerobic conditions and stored in anaerobic jars to remove any oxygen
  13. 13. • Selective Media = Media used to encourage growth of some organisms while suppressing the growth of others • Differential Media = Media used to distinguish colonies of specific bacteria from other organisms • Enrichment Culture = media that mimics environmental conditions that favor the growth of a particular microbe but not another
  14. 14. Obtaining Pure Cultures • The most commonly used method to get pure cultures is the streak plate method
  15. 15. Growth of Bacterial Cultures • Bacterial cells divide by binary fission, some by budding • The time for a cell to divide is called generation time • 1-3 hours is typical for most bacteria • E.coli reproduces every 20 minutes!
  16. 16. Calculating Generation Time (Initial # of cells )X (2 number of generations )= # of cells • Example: A Taco Bell manager accidentally inoculated 5 cells of E. coli into the burrito meat. How many cells would there be after 4 hours if E.coli has a generation time of 20 minutes.
  17. 17. Phases of Growth • A bacterial growth curve shows the growth of cells over time • LAG PHASE • EXPONENTIAL PHASE • STATIONARY PHASE • DEATH PHASE
  18. 18. REVIEW CHAPTER 6 and • Describe physical • PAGE 185-186 • Review #’s: 2, 4, 10, 12 • Multiple Choice #’s: 8, 9 chemical requirements for growth • Label these test tubes with the type of oxygen-organism
  19. 19. GROUP TEACH • Page 178-read first 2 paragraphs • PLATE COUNTS-dilutions • FILTRATION • MPN • DIRECT MICROSCOPE COUNT Each group tell me: • Tell the method of measuring cell growth • Advantages/Disadvantages • When is it used • What is the process • Picture or Diagram

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