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Microbial Growth

Microbial Growth. Growth of Microbes. Increase in number of cells, not cell size One cell becomes colony of millions of cells. Growth of Microbes. Control of growth is important for infection control growth of industrial and biotech organisms. Factors Regulating Growth. Nutrients

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Microbial Growth

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  1. Microbial Growth

  2. Growth of Microbes • Increase in number of cells, not cell size • One cell becomes colony of millions of cells

  3. Growth of Microbes • Control of growth is important for • infection control • growth of industrial and biotech organisms

  4. Factors Regulating Growth • Nutrients • Environmental conditions: temperature, pH, osmotic pressure • Generation time

  5. Chemical Requirements • #1 = water! • Elements • C (50% of cell’s dry weight) HONPS • Trace elements • Organic • Source of energy (glucose) • Vitamins (coenzymes) • Some amino acids, purines and pyrimidines

  6. Nutritional Categories • Carbon sources • CO2 = autotroph • organic = heterotroph • Energy sources • sunlight = phototroph • organic = chemotroph

  7. A “Chemoheterotroph”would….. • Derive both carbon and energy from organic compounds

  8. A “Chemoorganic autotroph would be…. Derives energy from organic compounds and carbon source from inorganic compounds A related ancient group….. Lithoautotroph Neither sunlight nor organics used, rather it relies totally on inorganics

  9. Nutritional Categories • Saprobe – lives on organic matter of dead organisms • Parasite – lives on organic matter of living host = pathogens

  10. Environmental Factors Influencing Growth • Temperature • O2 • pH • Osmotic Pressure • Others: radiation, atmospheric pressure

  11. Temperature Optima • Psychrophiles: cold-loving • Mesophiles: moderate temperature-loving • Thermophiles: heat-loving • Each has a minimum, optimum, and maximum growth temperature

  12. Fig. 7.8

  13. Temperature Optima • Optimum growth temperature is usually near the top of the growth range • Death above the maximum temp. comes from enzyme inactivation • Mesophiles most common group of organisms • 40ºF (5°C) slows or stops growth of most microbes

  14. Oxygen Requirements • Obligate aerobes – require O2 • Facultative anaerobes – can use O2 but also grow without it • Obligate anaerobes – die in the presence of O2

  15. pH • Most bacteria grow between pH 6.5 and 7.5 • Acid (below pH 4) good preservative for pickles, sauerkraut, cheeses • Acidophiles can live at low pH

  16. pH • Many bacteria and viruses survive low pH of stomach to infect intestines • Helicobacter pylori lives in stomach under mucus layer

  17. Measuring Bacterial Growth

  18. Bacterial Division • Bacteria divide by binary fission • Alternative means • Budding • Conidiospores (filamentous bacteria) • Fragmentation

  19. Fig. 7.13

  20. Generation Time • Time required for cell to divide/for population to double • Average for bacteria is 1-3 hours • E. coli generation time = 20 min • 20 generations (7 hours), 1 cell becomes 1 million cells!

  21. Fig. 7.14a

  22. Plotting growth on graphs

  23. Standard Growth Curve

  24. Phases of Growth • Lag phase – making new enzymes in response to new medium • Log phase – exponential growth • Desired for production of products • Most sensitive to drugs and radiation during this period

  25. Phases of Growth • Stationary phase – • nutrients becoming limiting or waste products becoming toxic • death rate = division rate • Death phase – death exceeds division

  26. Measuring Growth • Direct methods – count individual cells • Indirect Methods – measure effects of bacterial growth

  27. Fig. i7.6

  28. Fig. 7.17

  29. Turbidity

  30. Metabolic Activity

  31. Dry Weight

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