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Chapter 6

Chapter 6. Microbial Growth. The Requirements for Growth: Physical Requirements. Temperature Minimum growth temperature Optimum growth temperature Maximum growth temperature. Temperature. Celcius to fahrenheit conversion. Figure 6.1. Psychrophiles: cold-loving microbes

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Chapter 6

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  1. Chapter 6 Microbial Growth

  2. The Requirements for Growth: Physical Requirements • Temperature • Minimum growth temperature • Optimum growth temperature • Maximum growth temperature

  3. Temperature Celcius to fahrenheit conversion Figure 6.1

  4. Psychrophiles: cold-loving microbes • Psychrotrophs (“moderate psychrophiles”): cold tolerant; cause food spoilage • Mesophiles: moderate-temperature-loving microbes • Thermophiles: hot-loving microbes

  5. Figure 6.2

  6. The Requirements for Growth: Physical Requirements • pH • Most bacteria grow between pH 6.5 and 7.5 • Molds and yeasts grow between pH 5 and 6 • Acidophiles • Alkalophiles • neutralophiles

  7. The Requirements for Growth: Physical Requirements • Water - (osmotic pressure) • Hypertonic environments can cause plasmolysis • Extreme or obligate halophiles require high [salt] • Facultative halophiles tolerate high [salt] • Hypotonic environment may cause cells to burst

  8. Figure 6.4

  9. The Requirements for Growth: Chemical Requirements • Carbon • Form structural and functional organic molecules; energy source • Heterotrophs • Autotrophs

  10. The Requirements for Growth: Chemical Requirements • Nitrogen • Used to make amino acids (proteins), nucleic acids • Bacteria acquire nitrogen from various sources: • Most by decomposing proteins • Some bacteria use NH4+(ammonium), NO3 (nitrate), or N2 (nitrogen gas)

  11. The Requirements for Growth: Chemical Requirements • Sulfur • Is used to make some amino acids, thiamine, biotin • Bacteria acquire sulfur from various sources: • Most bacteria decompose proteins • Some bacteria use SO42 (sulfate) or H2S • Phosphorus • Is used to make DNA, RNA, ATP, and membranes

  12. The Requirements for Growth: Chemical Requirements • Trace Elements • Inorganic elements required in small amounts • Usually as enzyme cofactors

  13. The Requirements for Growth: Chemical Requirements • Organic Growth Factors • Organic compounds that the microbe cannot synthesize • Obtained from the environment • Vitamins, amino acids, other compounds

  14. The Requirements for Growth: Chemical Requirements • Oxygen (O2)

  15. Culture Media • Medium: Nutrients prepared for microbial growth • Sterile: No living microbes • Inoculation: Introduction of microbes into medium • Inoculum: the microbes used to inoculate a medium • Culture: Microbes growing in/on a medium

  16. Agar • Complex polysaccharide • Used as solidifying agent for culture media in Petri plates, slants, and deeps • Generally not metabolized by microbes • Liquefies at 100°C • Solidifies ~40°C

  17. Culture Media • Chemically Defined Media: Exact chemical composition is known • Complex Media: Extracts and digests of yeasts, meat, or plants • i.e. Nutrient broth • i.e. Nutrient agar • Extract: water soluble preparation of broken down cells • Digest: water soluble preparation of partially broken down proteins

  18. Culture Media Table 6.2 & 6.4

  19. Anaerobic Culture Methods • Reducing media • Contains thioglycolate that combines with O2 • http://www.mc.maricopa.edu/~johnson/labtools/Dbiochem/oxy.html • Oxyrase – commercial product that reduces O2 to H2O (removes the oxygen)

  20. Anaerobic Culture Methods • Anaerobic jar • Chemical reactions remove oxygen Figure 6.5

  21. Capnophiles require high CO2 • Candle jar • CO2-packet Figure 6.7

  22. Selective Media • Suppresses unwanted microbes and allows desired microbes. • How? i.e. vary the [salt] or pH • (Enrichment Media: encourages growth of microbes present in small numbers and/or are fastidious) • Fastidious: require specific nutrients • How? Use special ingredient

  23. Differential Media • Make it easy to distinguish colonies of different microbe types. • How? • i.e. hemolysis on blood agar • i.e. mannitol fermentation • i.e. pH indicator (color)

  24. Pure Culture • A pure culture contains only one species or strain • A colony is a population of cells arising from a single cell or spore or from a few attached cells • A colony = colony-forming unit (CFU)

  25. Preserving Bacterial Cultures • Deep-freezing: -50°C to -95°C • Lyophilization (freeze-drying): Frozen (-54° to -72°C) and dehydrated in a vacuum; stored at room temp. • Bacteria can be preserved for years by these methods

  26. Reproduction in Prokaryotes • Binary fission

  27. Budding • Microbial growth = increase in number of cells, not cell size

  28. Generation Time • The time period for one cell to divide; therefore, for the population to double • Generation time varies from microbe to microbe • E.coli = 20 – 30 minutes • Mycobacterium tuberculosis = 15 – 20 hours

  29. Figure 6.14

  30. Direct Measurements of Microbial Growth • Plate Counts: Perform serial dilutions of a sample Figure 6.15, top portion

  31. Plate Count • After incubation, count colonies on plates that have 25-250 colonies (CFUs) Figure 6.15

  32. Direct Measurements of Microbial Growth • Filtration: used for small population samples • i.e. Waste water treatment testing Figure 6.17a, b

  33. Direct Measurements of Microbial Growth Figure 6.19

  34. Indirect Measurements of Microbial Growth • Measuring turbidity of culture using a spectrophotometer Figure 620

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