The Effect of Physical and Chemical Conditions on Microbial Growth Flashcards
Temperature
is a major environmental factor controlling microbial growth.
Cardinal Temperatures
The minimum, optimum, and maximum temperatures at which an organism grows.
- are characteristic of each different organism
How can Microorganisms be classified into groups by their growth temperature optima?
- Psychrophile: low temperature
- Mesophile: midrange temperature
- Thermophile: high temperature
- Hyperthermophile: very high temperature
What is Mesophiles? Where are they found in?
Organisms that have midrange temperature optima.
- Found in:
- Warm-blooded animals
- Terrestrial and aquautic environments
- Temperate and tropical latitudes
Cold-Loving Microorganisms (Extremophiles)
Organisms that grow under very hot or very cold conditions
Cold-Loving Microorganisms (Psychrophiles)
- Organisms with cold temperature optima (<20oC)
- Inhabit permanently cold environments
- Deep ocean, Arctic and Antarctic environments
Cold-Loving Microorganisms (Psychrotolerant)
- Organisms that can grow at 0ºC but have optima of 20ºC to 40ºC
- More widely distributed in nature than true psychrophiles
Molecular adaptations that support psychrophily
- Production of enzymes that function optimally in the cold
- Modified cytoplasmic membranes
- High unsaturated fatty acid content
Heat-Loving Microorganisms
- Above ~65ºC, only prokaryotic life forms exist
- Chemoorganotrophic and chemolithotrophic species are present
- No phototrophy above approx. 70oC
- High prokaryotic diversity
- Both Archaea and Bacteria are represented
Thermophiles
organisms with growth temperature optima between 45ºC and 80ºC
- Terrestrial hot springs, very active compost
Hyperthermophiles
organisms with optima greater than 80ºC
- Inhabit hot environments, including boiling hot springs and seafloor hydrothermal vents that can experience temperatures in excess of 100ºC
Molecular adaptations to thermophily
- Specific modifications provide thermal stability to enzymes and proteins
- Modifications in cytoplasmic membranes to ensure heat stability
- Bacteria have lipids rich in saturated fatty acids
- Archaea have lipid monolayer rather than bilayer
Hyperthermophiles
produce enzymes widely used in industrial microbiology
- Example: Taq polymerase used to automate the repetitive steps in the
polymerase chain reaction (PCR) technique
- Hydrolytic enzymes including proteases, cellulases and lipases
What are the upper temperature limits for life?
- New species of thermophiles and hyperthermophiles are still being discovered
- Laboratory experiments with biomolecules suggest 140–150°C
Hyperthermophily & Evolution
- Hyperthermophiles may be the closest descendants of ancient microbes
- Hyperthermophilic Archaea and Bacteria are found on the deepest, shortest branches of the phylogenetic tree
- The oxidation of H2 is common to many hyperthermophiles
- May have been the first energy-yielding metabolism
Effects of pH on Microbial Growth
- The pH of an environment greatly affects microbial growth
- Some organisms have evolved to grow
best at low or high pH - Most organisms grow best between pH 6 and 8 → neutrophiles
Acidophiles
Organisms that grow best at low pH (<6)
Alkaliphiles
Organisms that grow best at high pH (>9)
Halophiles
grow best at reduced water potential; have a specific requirement for NaCl
- Many marine microbes
Extreme halophiles
Require high levels of NaCl for growth
- 15 – 30%
- Ex) Microbes from Great Salt lake or the Dead Sea
Halotolerant
can tolerate some reduction in water activity of environment but generally grow best at lower solute concentrations
- Ex) Staphylococcus aureus
- Lives on human skin
- Grows best at low NaCl
- But can tolerate up to 17.5%
Osmophiles
Organisms that grow with high sugar as solute
Xerophiles
Organisms able to grow in very dry environments
Specialized and rare organisms
- Honey, jams and jellies do not have many organisms growing in them
- Beef jerky and salted cod
Obligate aerobes
- Require oxygen to live
- grows only in the oxic zone at the top of the tube
Strict anaerobes
- do not require oxygen and may even be killed by exposure
- grows only in the anoxic zone at the bottom of the tube
Facultative aerobes
- can live with or without oxygen, they use oxygen when it is available
- grows throughout the tube
- Better growth occurs in the oxic zone, where it can generate energy by aerobic
respiration
Aerotolerant anaerobes
- can tolerate oxygen and grow in its presence even though they cannot use it
- grows well throughout the tube
- Doesn’t use O2
- Not harmed by O2
Microaerophiles
- can use oxygen only when it is present at levels reduced from that in air
- grows in a narrow band between the oxic and anoxic zones
- Needs O2 for aerobic respiration
- Killed by atmospheric O2 levels
Differences in oxygen use/tolerance can be distinguished using?
Thioglycolate Broth
Thioglycolate Broth
- Complex medium that separates microbes based on oxygen requirements
- Thioglycolate reacts with oxygen creating an anaerobic environment
- Oxygen can penetrate only the top of the tube
- Contains an oxygen responsive dye that turns pink in the presence of oxygen and colorless when the oxygen is low or absent
Special Techniques are needed to grow anaerobic microbes.
- Reducing agents may be added to culture media to reduce oxygen
- Thioglycolate, cysteine, H2S and other sulfur containing compounds
- Removal of air, and replacement with an inert gas
- Ex) nitrogen or argon
What are the toxic forms of oxygen that can be formed spontaneously in the cell?
- Superoxide Anion
- Hydrogen Peroxide
- Hydroxyl Radical
What are the Enzymes that neutralize these toxic oxygen species?
- Catalase
- Peroxidase
- Superoxide dismutase
- Superoxide reductase
