Lecture 5: The Effects of Physical/Chemical Conditions on Microbial Growth Flashcards
______ is a major environmental factor controlling microbial
growth
Temperature
_______: the minimum, optimum, and maximum
temperatures at which an organism grows
Cardinal temperatures
T/F: cardinal temperatures are characteristic of each different organism
true
Microorganisms can be classified into groups by their growth temperature optima, what are these four groups?
Psychrophile
Mesophile
Thermophile
Hyperthermophile
______: low temperature
Psychrophile
_______: midrange temperature
Mesophile
________: high temperature
Thermophile
______: very high temperature
Hyperthermophile
what types of animals/environments are mesophiles in?
Warm-blooded animals
Terrestrial and aquatic environments
Temperate and tropical latitudes
________: organisms that grow under very hot or very cold conditions
extremophiles
_______:
* Organisms that can grow at 0ºC but
have optima of 20ºC to 40ºC
- More widely distributed in nature than
true psychrophiles
Psychrotolerant
what molecular adaptations that support psychophily?
production of enzymes that function optimally in the cold
modified membranes (high unsaturated fatty acids!!)
T/F: Above ~65ºC, only prokaryotic life forms exist
true! high prokaryotic diversity! both archaea and bacteria represented
T/F: No phototrophy above approx. 70C
true
_________:
* Organisms with cold temperature optima (<20C)
* Inhabit permanently cold environments
* Deep ocean, Arctic and Antarctic environment
Psychrophiles
________: organisms with growth temperature optima between
45ºC and 80ºC
* Terrestrial hot springs, very active compost
Thermophiles
_______: 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
Hyperthermophiles
T/F: Current temperature maximum record is held by an archaeon, Methanopyrus
kandleri, which can grow at 122C
true!
what are the molecular adaptations to thermophily?
specific modifications provide thermal stability to enzymes and proteins
modifications in cytoplasmic membranes
T/F: Hyperthermophiles produce enzymes widely used in industrial
microbiology
true!
T/F: Enzymes of thermophiles are more stable and tend to have lower activity than their mesophilic counterparts
false!
What are the upper temperature
limits for life?
Laboratory experiments with
biomolecules suggest 140–150°C
T/F: New species of thermophiles and
hyperthermophiles are still being discovered
true!
T/F: Hyperthermophiles may be the closest descendants of ancient microbes
true!
The oxidation of H2 is common to many hyperthermophiles (early Earth atmosphere had no carbon, need to be very simple to live off H2!)
May have been the first energy-yielding metabolism
T/F: the pH of an environment greatly affects
microbial growth
true!
Most organisms grow best between pH
6 and 8, what are they called?
neutrophiles
______: Organisms that grow best at low pH (<6)
acidophiles
_______: Organisms that grow best at high pH (>9)
alkaliphiles
what homeostatic effects MUST stay the same?
cytoplasmic membrane maintains its integrity at growth pH
internal pH must stay 7, close to neutral
what do we include in microbial media cultures to maintain homeostasis inside the cell?
buffers to maintain constant pH
Some bacteria produce acids
* Acetic, lactic, sulfuric acid = decreases the pH
Some bacteria grow on amino acids
* Releases ammonia = increases the pH
________ (aw): water availability; expressed in physical terms
Water activity
________: is defined as the ratio of vapor pressure of air in equilibrium with a
substance or solution to the vapor pressure of pure water
Reflects the amount of water that is interacting with ions and polar compounds in solution
water activity
T/F: Typically, the cytoplasm has a higher solute concentration than the
surrounding environment
true! water will want to move into the cell, creates turgor pressure
______: grow best at reduced water potential;
have a specific requirement for NaCl
Halophiles
- Many marine microbes
________: Require high levels of NaCl for growth
Extreme halophiles
* 15 – 30%
* Ex) Microbes from Great Salt lake or the Dead Sea
______: can tolerate some reduction in
water activity of environment but generally grow
best at lower solute concentrations
Halotolerant
ex: s aureus, lives on human skin (sweat causes low concentrations of NaCl in env.)
________: Organisms that grow with high sugar as solute
Osmophiles
_______: Organisms able to grow in very dry environments
Xerophiles
T/F: Honey, jams and jellies do not have many organisms growing in them
true! very low moisture contents make it difficult to sustain life/growth, high solute concentration kills bacteria!
T/F: High osmolarity created with NaCl is not used to select for acid producing
microorganisms
false!
Used for sauerkraut and pickle fermentation
Combination of high salt and low pH prevents the growth of most pathogens
in the completed product
how do cells combat low water activity in surrounding environment?
Pumping inorganic ions from environment into cell
Synthesizing or concentrating organic solutes
________: compounds used by cell to counteract low water activity in surrounding environment
Compatible solutes
_______: require oxygen to live
Obligate aerobes
_____: do not require oxygen and may even be killed by
exposure
Strict anaerobes
______: can live with or without oxygen, they use oxygen when it is available
Facultative aerobes
______: can tolerate oxygen and grow in its presence
even though they cannot use it
Aerotolerant anaerobes
_____: can use oxygen only when it is present at levels
reduced from that in air
Microaerophiles
how can we distinguish differences in oxygen use/tolerance?
using thioglycolate broth
_______: Complex medium that separates microbes based on oxygen requirements
thioglycolate broth
how does thioglycolate work?
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
what will an obligate aerobe do in Thioglycolate broth?
grows only in the oxic zone at the top of the tube
what will a strict anaerobe do in Thioglycolate broth?
grows only in the anoxic zone at the bottom of the tube
what will a falcultative anaerobe do in Thioglycolate broth?
grows throughout the tube
Better growth occurs in the oxic zone, where it can generate energy by aerobic
respiration
what will a microaerophile do in Thioglycolate broth?
grows in a narrow band between the oxic and anoxic zones
- Needs O2 for aerobic respiration
- Killed by atmospheric O2 levels
what will a aerotolerant anaerobe do in Thioglycolate broth?
grows well
throughout the tube
* Doesn’t use O2
* Not harmed by O2
what needs to happen to grow anaerobic microbes? what special techniques are used?
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 three toxic forms of oxygen that can form spontaneously in the cell?
Superoxide anion
Hydrogen peroxide
Hydroxyl radical
what 4 enzymes are present inside the cell to neutralize toxic oxygen forms?
Catalase
Peroxidase
Superoxide dismutase
Superoxide reductase
why can’t obligate anaerobes combat oxidative stress? neutralize these toxic forms of oxygen?
they lack some or all of the enzymes that neutralize toxic oxygen!
