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Chapter 6

Chapter 6. Microbial Growth. Microbial Growth. Increase in number of cells, not cell size Populations Colonies. The Requirements for Growth. Physical requirements Temperature pH Osmotic pressure Chemical requirements Carbon Nitrogen, sulfur, and phosphorous Trace elements Oxygen

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Chapter 6

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  1. Chapter 6 Microbial Growth

  2. Microbial Growth • Increase in number of cells, not cell size • Populations • Colonies

  3. The Requirements for Growth • Physical requirements • Temperature • pH • Osmotic pressure • Chemical requirements • Carbon • Nitrogen, sulfur, and phosphorous • Trace elements • Oxygen • Organic growth factor

  4. Example: Psychrotrophs • Grow between 0°C and 20–30°C • Cause food spoilage

  5. 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

  6. Plasmolysis Figure 6.4

  7. Chemical Requirements • Carbon: • The structural ‘backbone’ of organic molecules • ~Half the dry weight of a typical bacterial cell is C • Carbon Sources: • Chemoheterotrophs: use organic carbon sources (The specific organic carbon source(s) that can be used are determined by an organism’s DNA) • Chemo- and Photo- Autotrophs: use CO2

  8. Chemical Requirements • Nitrogen • Needed for amino acids and proteins, nitrogen bases (DNA, RNA, ATP) • ~ 14% of dry weight of a bacterial cell is N • Most bacteria decompose proteins and rearrange these amino acids to form the proteins and other N-containing molecules they need • Some bacteria use NH4+ (ammonium) or NO3–(nitrate) • Many photosynthetic bacteria use N2 in the atmosphere during nitrogen fixation. N2 is 80% of Earth’s atmosphere. • See SLIDE 9

  9. Figure 27.4

  10. Chemical Requirements • Sulfur • In amino acids, vitamins (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, changes little • Source: Rocks, sea sediment, soil, solubilized by the acid produced by bacteria, not returned to the atmosphere like CO2, N2, SO2 • Other: K, Mg, Ca, inorganic trace elements (Fe, Zn, Cu, etc.- often used as enzyme cofactors)- found in tap water

  11. The Effect of Oxygen (O2) on Growth Table 6.1

  12. Q&A • Oxygen in the atmosphere is essential for human life. How can some bacteria grow in the absence of oxygen?

  13. Biofilms Clinical Focus, p 164

  14. Reproduction in Prokaryotes • Binary fission • Budding • Conidiospores (actinomycetes) • Fragmentation of filaments

  15. Binary Fission Figure 6.12a

  16. Generation Time • Time it takes for a cell to divide; therefore, the time it takes for a population to double • If a bacterium has a generation time of 2 hours, and the population begins with 10 cells, how many cells will be in the population after 10 hours?

  17. Phases of GrowthBacterial Growth Curve Figure 6.15

  18. If two mice started a family within a fixed enclosure, with a fixed food supply, would the population curve be the same as a bacterial growth curve? 6-15

  19. Serial Dilutions Figure 6.16

  20. Plate Counts • After incubation, count colonies on plates that have 25–250 colonies (CFUs) Figure 6.16

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