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Chapter 3

Chapter 3. Microbial Growth. Microbial Growth. Microbial growth is the increase in number of cells, not cell size. The Requirements for Growth: Physical Requirements. Temperature Minimum growth temperature Optimum growth temperature Maximum growth temperature. Temperature. Figure 6.1.

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Chapter 3

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  1. Chapter 3 Microbial Growth

  2. Microbial Growth • Microbial growth is the increase in number of cells, not cell size

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

  4. Temperature Figure 6.1

  5. Psychrotrophs • Grow between 0°C and 20-30°C • Cause food spoilage

  6. Psychrotrophs Figure 6.2

  7. 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 grow in acidic environments

  8. The Requirements for Growth: Physical Requirements • Osmotic pressure • Hypertonic environments, increase salt or sugar, cause plasmolysis • Extreme or obligate halophiles require high osmotic pressure • Facultative halophiles tolerate high osmotic pressure

  9. The Requirements for Growth: Physical Requirements Figure 6.4

  10. The Requirements for Growth: Chemical Requirements • Carbon • Structural organic molecules, energy source • Chemoheterotrophs use organic carbon sources • Autotrophs use CO2

  11. The Requirements for Growth: Chemical Requirements • Nitrogen • In amino acids and proteins • Most bacteria decompose proteins • Some bacteria use NH4+ or NO3– • A few bacteria use N2 in nitrogen fixation • Sulfur • In amino acids, thiamine and biotin • Most bacteria decompose proteins • Some bacteria use SO42– or H2S • Phosphorus • In DNA, RNA, ATP, and membranes • PO43– is a source of phosphorus

  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 • Oxygen (O2) Table 6.1

  14. Toxic Forms of Oxygen • Singlet oxygen: O2 boosted to a higher-energy state • Superoxide free radicals: O2– • Peroxide anion: O22– • Hydroxyl radical (OH)

  15. The Requirements for Growth: Chemical Requirements • Organic growth factors • Organic compounds obtained from the environment • Vitamins, amino acids, purines, and pyrimidines

  16. Culture Media • Culture medium: Nutrients prepared for microbial growth • Sterile: No living microbes • Inoculum: Introduction of microbes into medium • Culture: Microbes growing in/on culture medium

  17. 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

  18. Culture Media • Chemically defined media: Exact chemical composition is known • Complex media: Extracts and digests of yeasts, meat, or plants • Nutrient broth • Nutrient agar

  19. Culture Media Tables 6.2, 6.4

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