Microbial Growth

1
Microbial Growth
2
Growth of Microbes

• Increase in number of cells, not cell size
• One cell becomes colony of millions of cells

3
Growth of Microbes

• Control of growth is important for
• infection control
• growth of industrial and biotech organisms

4
Factors Regulating Growth

• Nutrients
• Environmental conditions temperature, pH,
  osmotic pressure
• Generation time

5
Chemical Requirements

• 1 water!
• Elements
• C (50 of cells dry weight) HONPS
• Trace elements
• Organic
• Source of energy (glucose)
• Vitamins (coenzymes)
• Some amino acids, purines and pyrimidines

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Nutritional Categories

• Carbon sources
• CO2 autotroph
• organic heterotroph
• Energy sources
• sunlight phototroph
• organic chemotroph

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A Chemoheterotrophwould..

• Derive both carbon and energy from organic
  compounds

8
A Chemoorganic autotroph would be.

• Derives energy from organic compounds and carbon
  source from inorganic compounds
• A related ancient group..
• Lithoautotroph
• Neither sunlight nor organics used, rather it
  relies totally on inorganics

9
Nutritional Categories

• Saprobe lives on organic matter of dead
  organisms
• Parasite lives on organic matter of living host
  pathogens

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Movement of WaterOsmosis
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Fig. 7.4
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Diffusion of Water

• Isotonic same solutes inside and outside, no
  water movement
• Hypotonic more solutes inside, water enters cell
• Hypertonic more solutes outside, water leaves
  cell

13
Movement of Molecules

• Facilitated diffusion higher to lower
  concentration, carrier molecule
• Active transport lower to higher, takes energy
• Group translocation lower to higher with
  chemical change
• Bulk transport endocytosis, phagocytosis,
  pinocytosis

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Facilitated Diffusion
15
Active Transport
Lower to higher solute concentration Requires ATP
16
Group Translocation
17
Phagocytosis Endocytosis
18
Environmental Factors Influencing Growth

• Temperature
• O2
• pH
• Osmotic Pressure
• Others radiation, atmospheric pressure

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Temperature Optima

• Psychrophiles cold-loving
• Mesophiles moderate temperature-loving
• Thermophiles heat-loving
• Each has a minimum, optimum, and maximum growth
  temperature

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Fig. 7.8
21
Temperature Optima

• Optimum growth temperature is usually near the
  top of the growth range
• Death above the maximum temp. comes from enzyme
  inactivation
• Mesophiles most common group of organisms
• 40ºF (5C) slows or stops growth of most microbes

22
Oxygen Requirements

• Obligate aerobes require O2
• Facultative anaerobes can use O2 but also grow
  without it
• Obligate anaerobes die in the presence of O2

23
Oxygen Tolerance

• Aerotolerant do not use O2 but can grow when it
  is present
• Often ferment glucose to lactic acid
• Microaerophiles require O2 but grow only in
  concentrations lower than air

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• Classify the Growth in each tube
• Aerotolerant anaerobe
• Facultative anaerobe
• Microaerophile
• Obligate aerobe
• Obligate anaerobe

25

• Classify the Growth in each tube
• Aerotolerant anaerobe
• Facultative anaerobe(s)
• Microaerophile
• Obligate aerobe
• Obligate anaerobe

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Toxic Forms of Oxygen

• Singlet oxygen (1O2) very reactive
• Superoxide free radicals (O2.)
• Neutralized by superoxide dismutase (SOD)

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Toxic Forms of Oxygen

• Peroxide anions (O2-2)
• H2O2 broken down by catalase and peroxidase
• Hydroxyl radical (OH-) very reactive

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Fig. 7.10b
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Candle jar

• Provides low O2, high CO2

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pH

• Most bacteria grow between pH 6.5 and 7.5
• Acid (below pH 4) good preservative for pickles,
  sauerkraut, cheeses
• Acidophiles can live at low pH

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pH

• Many bacteria and viruses survive low pH of
  stomach to infect intestines
• Helicobacter pylori lives in stomach under mucus
  layer

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Osmotic Pressure

• Bacteria 80-90 water
• High salt in surrounding environment leads to
  water loss and plasmolysis
• Cells plasma membrane shrinks, cell growth
  inhibited

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Drying and High Osmolarity

• Salted fish, jerky, honey, sweetened condensed
  milk are preserved by pulling water out of
  bacteria
• Hypotonic medium (low osmolarity) may lyse
  bacteria without cell walls

34
Ecological Associations

• Symbiotic close nutritional relationship
• Mutualism both benefit
• Commensalism commensal benefits, host not
  harmed
• Parasitism parasite benefits, host harmed

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Measuring Bacterial Growth
36
Bacterial Division

• Bacteria divide by binary fission
• Alternative means
• Budding
• Conidiospores (filamentous bacteria)
• Fragmentation

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Fig. 7.13
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Generation Time

• Time required for cell to divide/for population
  to double
• Average for bacteria is 1-3 hours
• E. coli generation time 20 min
• 20 generations (7 hours), 1 cell becomes 1
  million cells!

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Fig. 7.14a
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Plotting growth on graphs
41
Standard Growth Curve
42
Phases of Growth

• Lag phase making new enzymes in response to new
  medium
• Log phase exponential growth
• Desired for production of products
• Most sensitive to drugs and radiation during this
  period

43
Phases of Growth

• Stationary phase
• nutrients becoming limiting or waste products
  becoming toxic
• death rate division rate
• Death phase death exceeds division

44
Measuring Growth

• Direct methods count individual cells
• Indirect Methods measure effects of bacterial
  growth

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Fig. i7.6
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Fig. 7.17
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Turbidity
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Metabolic Activity
49
Dry Weight
50
Microbe of the Week
Thermus aquaticus

• A chemotrophic thermophilic
• bacterium from Yellowstone
• Thrives at 70 C ( 160 F)
• A Gram negative cell with a a think PG cell wall
  !
• The source of several enzymes used in
  biotechnology that operate at high temperature
• DNA polymerase (Taq polymerase)

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Microbe of the Week

• Thermus aquaticus
• Taq DNA polymerase is used in the Polymerase
  Chain Reaction (PCR) for amplifying, detecting
  and profiling DNA