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The Requirements for Growth

The Requirements for Growth. Physical requirements Temperature pH Osmotic pressure Chemical requirements Carbon Nitrogen, sulfur, and phosphorous Trace elements Oxygen Organic growth factor. Examples. Example: Psychrotrophs: Grow between 0°C and 20–30°C Many cause food spoilage

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The Requirements for Growth

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

  2. Examples • Example: Psychrotrophs: Grow between 0°C and 20–30°C • Many cause food spoilage • Extreme Thermophiles • Some microbes can live at 100°C at the bottom of the Ocean. How?

  3. Plasmolysis Figure 6.4

  4. 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

  5. Chemical Requirements • Nitrogen • Needed for amino acids (proteins), nitrogen bases (DNA, RNA, ATP) • ~ 14% of dry weight of a bacterial cell is N • Most bacteria decompose proteins in the environment from other organisms, 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 6

  6. Look for common terms among the various cycles (Example: Decomposition)

  7. Chemical Requirements • Sulfur • In amino acids, vitamins (thiamine and biotin) • Most bacteria decompose proteins • Some bacteria use SO42– or H2S for energy/e- donor/acceptor • 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

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

  9. Biofilms Clinical Focus, p 164

  10. Binary Fission Figure 6.12a

  11. 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?

  12. Phases of GrowthBacterial Growth Curve Figure 6.15

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