Chapter 6
Microbial Nutrition and Growth
Microbial Growth
• Microorganisms are found in the harshest of
environments
–
–
–
–
Deep ocean
Volcanic vents
Polar regions
Other planets?
• Each species has limited environmental ranges in which
it can grow
– _______________________________(some can survive in
boiling hot springs but cannot be cultivated at room temp)
– _________________________
– _________________________
Growth Requirements
• Microbial growth
–
• Result of microbial growth is discrete colony
–
• __________________results in growth
Generation Time (Doubling Time)
• Time required for a cell to grow and divide
• Dependent on chemical and physical conditions
• 10 minutes to 3 hours or more
• E. coli - 20 minutes/10 hours
• Mycobacterium tuberculosis - 16 Hrs/48+ hours
• Example:
– 10 cells of a food borne illness pathogen in potato
salad, sitting for 4 hrs in a warm room, are capable
of multiplying to more than 40,000 cells
Number of live cells (log)
Figure 6.20 Typical microbial growth curve
Time
Growth Requirements
• Organisms use a variety of nutrients for
their energy needs and to build organic
molecules for cellular structures
• Most common nutrients contain necessary
elements such as ____________________
________________________
Sources of Carbon
•
– Organisms that utilize an inorganic source of
carbon (carbon dioxide)
– Make their own food
•
– Catabolize organic molecules (proteins,
carbohydrates, and fatty acids)
– Obtain food from others
Growth Requirements
• Nutrients: Chemical and Energy Requirements
– Oxygen requirements
•
•
•
•
•
Aerobes
Obligate Anaerobes
Facultative anaerobes
Aerotolerant anaerobes
Microaerophiles
Oxygen
• Bacteria can be classified base on their oxygen
requirements
• FT tube
Absolute
requirement for
Oxygen
Grow better
when O2 is
present but can
grow without it
Cannot
grow/multiply
in the
presence of O2
Small O2
requirement, high
concentrations are
inhibitory
Indifferent to O2
can grow in its
presence but they
do not use it to
transform energy
Oxygen is lethal to some organisms
• All organisms produce superoxide ( O2-)
• Superoxide is toxic to cells (steals electrons)
• Superoxide must be neutralized
Superoxide dismutase
•
• O2- + O2- + 2 H+ -------> H2O2 + O2
• Hydrogen peroxide is also toxic to cells and it
must be neutralized
Catalase
•
• 2 H2O2 --------> 2 H2O + O2
• Obligate Anaerobes lack:
– Superoxide dismutase ( SOD )
– Catalase
– Therefore oxygen is toxic to them and they cannot
survive
Nitrogen
• Contained in many organic compounds
–
–
– 14% of dry weight of microbial cells
• Growth limiting nutrient
– Growth ceases due to in sufficient N sources for
proteins and nucleotides
• Acquisition of Nitrogen
– Nitrate reduction to ammonium
– Recycling nitrogen from their amino acids and
nucleotides
Growth Requirements
• Physical Requirements
– Temperature
• Effect of temperature on proteins
–
• Effect of temperature on membranes of cells
– If too low, _________________________________
– If too high, ______________________
Figure 6.4 Microbial growth-overview
Classifying organisms by temperature
requirements
– __________________(cold loving microbes )
• -5C – 20C
– _____________(moderate temp. loving microbes)
• 15 C - 45 C
– __________________(heat loving microbes)
• 45C – 80C
– ____________________ (Extreme heat loving)
• 70C +
Figure 6.5 Four categories of microbes based on temperature ranges for growth
Growth rate
Thermophiles
Mesophiles
Psychrophiles
Temperature (°C)
Hyperthermophiles
Figure 6.6 An example of psychrophile
Physical requirements: pH
• Most bacteria grow between pH 6.5 - pH 7.5 –
________________
• ________________: above pH 8.5
• ________________: below pH 5.5
• Very few can grow at below pH 4.0
– many foods, such as sauerkraut, pickles, and cheeses are
preserved from spoilage by acids produced during
fermentation
– There are microorganisms that grow in
environments with a pH of less than one
Water
• All microorganisms require water for growth
• Certain environments may contain substances
such as salt that interact with water
molecules, which makes water unavailable.
Water
• If the solute concentration is higher in the
medium than the cell? What happens?
– Solute is the dissolved substance (salt, sugars,…)
•
Salt
• Halophiles (halo means salt)
– ___________________: organisms that actually
__________high salt concentrations
– _____________________: ___________high salt
concentrations
• Staphylococcus aureus: salt tolerant organism which
colonizes human skin
• Opportunistic pathogen
Culturing Microorganisms
• Culture Media
– Majority of prokaryotes have not been grown
in culture medium
• Selective media
• Differential media
• Selective and Differential
Selective Media
• _____________the growth of some bacteria
while ___________for the growth of others
Figure 6.12 An example of the use of a selective medium
Bacterial colonies
pH 7.3
Fungal colonies
pH 5.6
Differential Media
•
• Example:
– Blood Agar Plates (TSA with 5% sheep blood)
• used to differentiate different __________________
– _________Hemolytic
»
» A green zone appears around the colony
– _________Hemolytic
»
» Clear zone appears around the colony
– _________Hemolytic
»
» No change to media
Selective and Differential Media
• Mannitol Salt Agar
– _________________for ____________________
• Mannitol is a ____________
• Not all organisms can utilize this sugar
– ____________for _______________organisms
• High salt concentration (7.5%) inhibits most bacteria
– ___________Indicator
•
Eosin Methylene Blue (EMB)
• ______________for Gram Negative coliforms
–
• Eosin makes this media _________for 2 major
coliforms: E. coli and Enterobacter aerogenes
Why are the colonies on the left larger
than the colonies in the middle?