Chapter 1 Lecture 9/14 Flashcards
Media Type by function (specialized media)
General growth media
Enriched media
Selective media
Differential media
Enriched media
can be used to increase a particular population of microbes with a specific property from a mixture of cell types
Selective media
allows for isolation of microbes with specific properties
Differential media
allows certain microbes to be recognized based on visual reactions in the medium
Notes to obtaining a pure culture
One of the benefits of a solid medium is that cells are held in place on the surface and can be isolated.
This can lead to separating a mixture of cells into a pure population.
There are 3 methods for separating cells on a plate.
3 methods for separating cells on a plate
Streak plate method
Spread plate method
Pour plate method
Nitrogen
amino acids, purines, pyrimidines, some carbohydrates, lipids, enzyme cofactors etc.
supplied in numerous ways
-Metabolism of amino acids, nitrates, ammonia, from atmosphere
-Nitrogen Fixation
Phosphorus
nucleic acids, phospholipids, coenzymes, some proteins, etc.
Common phosphorous sources
Inorganic phosphate
Organic molecules containing a phosphoryl group
Sulfur
amino acids, coenzymes
Obtained from 2 sources
Amino acids cysteine and methonine
Sulfate
-assimilatory sulfate reduction
sulfatesulfitehydrogen sulfide
Growth factors
organic compounds that cannot be synthesized by an organism but are essential for growth
3 classes of growth factors
1) amino acids -protein synthesis
2) purines/pyrmidines -nucleic acid synthesis
3) vitamins- enzyme cofactors, needed in very small amounts
Nutrient concentration
Growth rate –dependent on amounts of nutrients in environment
One key nutrient, available in the lowest amount, will dictate how much growth can occur over time
Aerobes
Aerobes grow in the presence of oxygen.
Obligate aerobes REQUIRE oxygen.
Microaerophiles grow best when there is less oxygen than normal.
Anaerobic growth
Anaerobic growth occurs without oxygen.
Aerotolerant anaerobes aren’t harmed by oxygen but don’t use it, either.
Obligate anaerobes cannot grow when oxygen is present.
Facultative anaerobes CAN use oxygen but can also grow in the absence of oxygen.
Thioglycolate Broth
Reducing compound which shows gradient of compound
Less oxygen at bottom than at top
Obligate aerobe
Facultative anerobe
Aerotolerant anaerobe
Strict anaerobe
Microaerophile
Factors affecting microbial growth
Effects of oxygen on microbial growth
Often determined by what defenses are available against oxygen’s negative effects in the cell
Reactive Oxygen Species
oxygen easily reduced to toxic reactive oxygen species (ROS)
O2 + e- –> O2- (superoxide radical)
O2- + e- + 2H+ –> H2O2 (hydrogen peroxide)
H2O2 + e- + H+ –> H2O + OH (hydroxyl radical)
Enzymes that protect against toxic O2 products
Aerobes produce protective enzymes
2O2- + 2H+ –(superoxide dismutase)–> O2 + H2O2
2H2O2 –(catalase)–> 2H2O + O2
H2O2 + NADH + H+ –(peroxidase)–> 2H2O + NAD+
Strict Anaerobic Microbes
*Strict anaerobic microorganisms lack
- Superoxide dismutase
- Catalase
*These microbes cannot tolerate O2
*Anaerobes must be grown without O2
- work station with incubator
- gaspak anaerobic system
An Anaerobic Workstation
Incubator
Airlock
Gloves
The GasPak Anaerobic System
Catalyst chamber
Gas generator envelope
Lid
Lockscrew
Clamp
Rubber gasket seal
Anaerobic indicator strip
pH
Effects of pH on microbial growth
Microbes have an optimal pH range for growth.
Acidophiles = pH < 5.5
Neutrophiles = pH 5.5 to 8.5
Alkalophiles = pH > 8.5
hypotonic solution
(higher osmotic concentration outside)
- water enters the cell
- cell swells may burst
hypertonic
(lower osmotic concentration outside)
- water leaves the cell
- membrane shrinks from the cell wall (plasmolysis) may occur
halophiles
grow optimally in the presence of NaCl or other salts at a concentration above about 0.2M
extreme halophiles
require salt concentrations of 2M and 6.2M
Compatible solutes
molecules that can be kept at high internal concentration
Solutes and Water Activity
water activity (aw)
amount of water available to organisms
Aw of distilled water is 1.0
Aw of milk is 0.97
Aw of dried fruits is 0.5
Osmotolerant microbes
Osmotolerant microbes can grow over wide ranges of water activity
(e.g., Staphylococcus aureus 3M NaCl)
Temperature
Effects of temperature on microbial growth
Different microbes have different optimal temperature growth ranges.
Cardinal Growth Temperatures
Minimal
Maximal
Optimal
psychrophiles
0 to 20 C
psychrotrophs
0 to 35 C
mesophiles
20 to 45 C
thermophiles
55 to 85 C
hyperthermophiles
85 to 113 C
Resistance to heat denaturation in cells
for DNA, more GC will help DNA maintain Hydrogen bonds and prevent some denaturation
Cell resistance to extreme cold
Everything slows down
Saturation to prevent Ice formation:
H2O in cell freezes into crystals and cuts everything, unless you saturate cells (mix with glycerol) to prevent ice formation, you can prevent death by ice
Structural adaptations
Adaptations of Thermophiles
protein structure stabilized by a variety of means
histone-like proteins stabilize DNA
membrane stabilized by variety of means
e.g., ether linkages (archaeal membranes)
