3 MicrobialNutritionGrowth
3 MicrobialNutritionGrowth
3 MicrobialNutritionGrowth
and Growth
MICROBIAL NUTRITION
Important for energy and construction
Nutrients
substances used in biosynthesis
energy production
1. Temperature:
B. Mesophiles: “Middle loving”. Most bacteria.
Include most pathogens and common spoilage organisms.
Best growth between 25o to 40oC.
Optimum temperature commonly 37oC.
Many have adapted to live in the bodies of animals.
Requirements for Growth
Physical Requirements
1. Temperature:
C. Thermophiles: “Heat loving”.
Optimum growth between 50 to 60oC.
Many cannot grow below 45oC.
Adapted to live in sunlit soil, compost piles, and hot
springs.
Some thermophiles form extremely heat resistant
endospores.
Extreme Thermophiles (Hyperthermophiles): Optimum
growth at 80oC to 140o C. Archaebacteria. Most live in
volcanic and ocean vents.
Growth Rates of Bacterial Groups at
Different Temperatures
Optimum Growth Temperature
Growth
optimum.
temperature
Maximum due
to enzyme
denaturation.
Temperature Ranges
Minimum due
to enzyme &
membrane
fluidity
problems.
Important for
food spoilage.
Psychotrophs
Most human i.e., organisms adapted to
pathogens are growth at body
mesophiles. temperature.
Mesophiles
Important source of heat-
stable enzymes (e.g., Taq
polymerase or laundry
detergent enzymes).
Thermophiles
Requirements for Growth
Physical Requirements
2. pH:
Most bacteria prefer neutral pH (6.5-7.5).
B. Neutrophiles:
Grow at pH 5.4 to 8.5.
Includes most human pathogens.
3. Osmotic Pressure:
Halophiles: Require moderate to large salt concentrations.
Ocean water contains 3.5% salt.
Most bacteria in oceans.
Extreme or Obligate Halophiles: Require very high salt
concentrations (20 to 30%).
Bacteria in Dead Sea, salt lakes.
Facultative Halophiles: Do not require high salt
concentrations for growth, but tolerate 2% salt or more.
Chemical Requirements
Macronutrients
Phototrophs
Light as energy source
Chemotrophs
use chemicals as energy sources, oxidation
of either organic or organic compounds
Electron sources
Lithotrophs
Use reduced inorganic compounds
Organothrophs
Use organic compounds
Requirements for Growth
Chemical Requirements
Hydrogen sulfide
Photolithotrophic autotrophs
Photoorganotrophic heterotrophs
Chemolithotrophic autotrophs
Chemoorganotrophic heterotophs
Mixotrophs?
Inorganic energy sources and organic C sources,
combination of autotrophic and heterotrophic
metabolism
Requirements for Growth
Chemical Requirements
5. Oxygen:
B. Facultative Anaerobes: Can use oxygen, but can
grow in its absence. Have complex set of enzymes.
Examples: E. coli, Staphylococcus, yeasts, and many
intestinal bacteria.
C. Obligate Anaerobes: Cannot use oxygen and are
harmed by the presence of toxic forms of oxygen.
Examples: Clostridium bacteria that cause tetanus and
botulism.
Requirements for Growth
Chemical Requirements
5. Oxygen:
D. Aerotolerant Anaerobes: Can’t use oxygen, but
tolerate its presence. Can break down toxic forms of
oxygen.
Example: Lactobacillus carries out fermentation
regardless of oxygen presence.
E. Microaerophiles: Require oxygen, but at low
concentrations. Sensitive to toxic forms of oxygen.
Example: Campylobacter.
Oxygen Requirements: The Shake Tube
Oxygen Requirements: The Shake Tube
The interval,
division to division,
is called the
Generation or
Doubling Time.
1. Plate count:
Most frequently used method of measuring bacterial populations.
Inoculate plate with a sample and count number of colonies.
Assumptions:
• Each colony originates from a single bacterial cell.
• Original inoculum is homogeneous.
• No cell aggregates are present.
Advantages:
• Measures viable cells
Disadvantages:
• Takes 24 hours or more for visible colonies to appear.
• Only counts between 25 and 250 colonies are accurate.
• Must perform serial dilutions to get appropriate numbers/plate.
Serial Dilutions are Used with the Plate Count Method to
Measure Numbers of Bacteria
Each colony on plate or filter arises from single live cell
Only counting live cells
Measuring Microbial Growth
Direct Methods of Measurement
2. Filtration:
Used to measure small quantities of bacteria.
Disadvantages:
• Cannot always distinguish between live and dead bacteria.
1. Turbidity:
As bacteria multiply in media, it becomes turbid.
Use a spectrophotometer to determine % transmission or
absorbance.
Multiply by a factor to determine concentration.
Advantages:
• No incubation time required.
Disadvantages:
• Cannot distinguish between live and dead bacteria.
2. Metabolic Activity:
As bacteria multiply in media, they produce certain products:
• Carbon dioxide
• Acids
Measure metabolic products.
Expensive
3. Dry Weight:
Bacteria or fungi in liquid media are centrifuged.
Resulting cell pellet is weighed.
Doesn’t distinguish live and dead cells.
4. Flow cytometer (FACS)
Florescent antibodies are
added to culture and cells in
small droplets are sent
through a detector single file
Computers count and
characterize cells as they
pass, and deflect cells with
desired characteristics
Can count and keep live cells
Biofilms