the requirements for growth
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Copyright © 2010 Pearson Education, Inc.
The Requirements for Growth
Physical requirements Temperature pH Osmotic pressure
Chemical requirements Carbon Nitrogen, sulfur, and phosphorous Trace elements Oxygen Organic growth factor
Copyright © 2010 Pearson Education, Inc.
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?
Copyright © 2010 Pearson Education, Inc. Figure 6.4
Plasmolysis
Copyright © 2010 Pearson Education, Inc.
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
Copyright © 2010 Pearson Education, Inc.
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
Copyright © 2010 Pearson Education, Inc.
Look for common terms among the various cycles (Example: Decomposition)
Copyright © 2010 Pearson Education, Inc.
Chemical Requirements Sulfur
In amino acids, vitamins (thiamine and biotin) Most bacteria decompose proteins Some bacteria use SO4
2– or H2S for energy/e- donor/acceptor
Phosphorus In DNA, RNA, ATP, and membranes PO4
3– 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
Copyright © 2010 Pearson Education, Inc. Table 6.1
The Effect of Oxygen (O2) on Growth
Copyright © 2010 Pearson Education, Inc. Clinical Focus, p 164
Biofilms
Copyright © 2010 Pearson Education, Inc. Figure 6.12a
Binary Fission
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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?
Generation Time
Copyright © 2010 Pearson Education, Inc. Figure 6.15
Phases of GrowthBacterial Growth Curve
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