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Chapter 7 Microbial Growth


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Microbe of the Day: Clostridium botulinum
Spore-former; lives in soil
Spores ingested, germinate and produce botulinum toxin --> paralysis
Strict anaerobe
Gram positive rod
Growth of Microbes
o Increase in number of cells, not cell size
o One cell becomes colony of millions of cells
o Control of growth is important for
– infection control
– growth of industrial and biotech organisms
Factors Regulating Growth
o Nutrients
o Environmental conditions: temperature, oxygen, pH, osmotic pressure
o Generation time
Chemical Requirements
o C (50% of cell’s dry weight)
o H, O, N, P, S
– Nitrogen fixation: transform N2 into NH4+
o Trace elements
o Needed for structural molecules and enzymes
Organic Growth Factors
o Source of energy
o Vitamins (coenzymes)
o Some amino acids, purines and pyrimidines.
Nutritional Categories
o Carbon sources

CO2 = autotroph
organic = heterotroph
o Energy sources

sunlight = phototroph
organic = chemotroph
lives on organic matter of dead organisms
lives on organic matter of living host = pathogen
Nutrient Uptake

Movement (diffusion) of water
Nutrient Uptake

same solute concentration inside and out; no water movement
Nutrient Uptake

more solutes inside; water enters cell
Nutrient Uptake

more solutes outside; water leaves cell
Movement of Molecules
Facilitated diffusion
higher to lower concentration, carrier molecule
Movement of Molecules
Active transport
lower to higher concentration, takes energy
Movement of Molecules
Group translocation
lower to higher concentration with chemical change

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