Transcript Bacterial Growth Unusual Growth Conditions Microbial Diversity

Bacterial Growth
Unusual Growth Conditions
Microbial Diversity
Parameters other than nutrition that affect
bacterial growth
1. pH—optimum pH of most organisms is 7.0
2. Water activity—most bacteria require a water activity
between 0.9 and 1.0
3. Osmolarity—The osmolarity of the bacterial cell cytoplasm
must be slightly greater than that of its environment for
cell growth
4. Oxygen—bacteria have a great variety of specifications
with respect to the amount of oxygen they require
5. Temperature—most organisms like 37oC
Cardinal Temperatures
The temperatures ranging from minimum to maximum
that allow for bacterial growth.
Minimum temperature: the lowest temperature at which an organism
can grow—lower temperatures do not support bacterial growth
Maximum temperature: the highest temperature at which an organism
can grow—higher temperatures do not support bacterial growth
Optimum temperature: the temperature at which growth is most rapid
The optimum temperature is always closer to the maximum
temperature than to the minimum temperature
Cardinal temperatures
The cardinal temperatures of bacteria
can vary from organism to organism
for a given class of organisms the cardinal temperatures
have a fixed range that supports their growth
Temperature classes of microbes
Mesophiles: midrange temperature optima circa 39oC
(example: E. coli found in warm blooded animals, soil
water in temperate or tropical zones)
Thermophiles: high temperature optima circa 60oC
Extremophiles
Psychrophiles: low temperature optima circa
4oC
Hyperthermophiles: extremely high
temperature optima circa 88oC or 106oC
Psychrophiles: Microbial Growth at cold
temperatures
Grow in cold environments where the temperature is CONSISTENT
Depths of the open ocean (1-3 oC)
Arctic or Antarctic polar regions that are permanently frozen or are
unfrozen for only a few weeks in the summer
--found in microscopic pockets of liquid water within frozen
material
Temperate regions with temperatures ranging from 20oC to 40oC
DO NOT support the growth of these organisms
Difficult to work with in a lab as sample containing the bacteria must
never warm up after sampling
Psychrotolerant bacteria
Can grow at temperatures of 0-4 oC but have a temperature optima
of 20-40 oC
Soil and water in temperate climates
Meat, dairy products and produce stored under refrigeration (4 oC)
Bacteria grow slowly –1-2 months to see signs of visible bacterial
growth.
Molecular considerations: How do psychrophiles
live in extremely cold environments?
Lipid and protein composition
Proteins are active at cold temps and easily denatured at moderate
temperatures due to their secondary structure
Alpha helix
Beta sheet
>>>
Beta sheet structures are more rigid than alpha helical structures: proteins
consisting predominantly of alpha helices are more flexible
Caveat: They are also more easily denatured
Molecular considerations: How do psychrophiles
live in extremely cold environments/Proteins
continued
The amino acids that make up the enzymes and proteins are
higher in polar AA content and lower in hydrophobic AA
content than in mesophiles—greater flexibility
Polar amino acids tend to interact with the surrounding
aqueous environment while hydrophobic amino acids
tend to interact with each other
Molecular considerations: How do psychrophiles
live in extremely cold environments/Lipids
Lipids that make up the cytoplasmic membrane do not gel
at cold temperatures
The fatty acids that make up the lipid bilayer are
polyunsaturated as opposed to saturated and can maintain a
semifluid state.
Think of butter or lard (saturated) vs vegetable oil
(polyunsaturated) !!!
Thermophiles
(temperature range 42oC to 68oC)
Compost piles (65oC)
Artificial environments
Hot water heaters and electric power plants
Hyperthermophiles
(temperature range 88oC to 106oC)
Found in hot springs and geysers that have temperatures near boiling
point (92oC to 100oC—depending on elevation)—Yellowstone Nat’l
Park/ Wyoming
Deep sea Hydrothermal vents (212oC)/primary food source
How to study hyperthermophiles
immerse microscope slides in hot springs/collect organisms
grow bacteria in pressurized vessels that reach temperatures
above boiling point.
Molecular considerations: How do
hyperthermophiles live in extremely hot
environments/Proteins
Amino acid composition and higher order structure of hyperthermophiles
not much different from that of mesophiles
Synthesize solutes within the cytoplasm that interact with the proteins
and stabilize these proteins (usually disaccharides)
Molecular considerations: How do
hyperthermophiles live in extremely hot
environments/Lipids
Archaebacteria >> Eubacteria
1. Lipids can be rich in saturated fatty acids—forms a stronger
hydrophobic environment—accounts for membrane stability
2. Specialized lipids of the archaebacteria
Specialized lipids of archaebacteria
The fatty acids of the lipid bilayer of hyperthermophillic
archaebacteria consist of long (C-40) carbon chains with repeating
units of isoprene sidechains
Isoprene
Specialized lipids of archaebacteria
The cytoplasmic membrane of hyperthermophilic archaebacteria
can be made up of lipid MONOLAYERS
Microbial growth at extreme pH
Acidophiles: organisms that grow best at low (acidic) pH
Obligate acidophiles: Thiobacillus—grows on reduced sulfur
(H2S) oxidized into sulfuric Acid (H2SO4) to gain energy.
High concentrations of H+ ions are required for membrane
stability—remove to neutral pH, cytoplasmic membrane dissolves
and cells lyse.
Alkaliphiles: organisms that grow best at high (alkaline) pH
Highly basic environments such as soda lakes
(Lake Hamara/Egypt) surrounding rocks rich in carbonate that
leaches into lake increasing the pH to 11.0
**these pH’s refer to the pH that the cells can GROW in, the pH of the
cytoplasmic compartment must be within the range of 4.5 – 9.5 to maintain the
Integrity of the macromolecules present in that compartment
Water activity/Osmolarity/Halophiles
4 classes of bacteria that tolerate various salt concentrations
Non-halophile: (E. coli) requires a high Aw cannot tolerate even
moderate levels of Na
Halotolerant: (St. aureus) can tolerate a reduction in Aw, but prefers
To grow in an environment where Na has not been added
Halophiles: prefers or needs to have Na in the environment
mild halophiles: NaCl ranging from 1 – 6% (sea water is 3%)
moderate halophiles: (6 – 15%)
EXTREME HALOPHILES: (15 –30%)
EXTREME HALOPHILES: (15 –30%)
Archaebacteria
Found in Great Salt Lake –Utah—concentrated sea water
(105 grams of Na2+ and 181 grams Cl- per liter of water)
High salt foods: sausages, marine fish, salt pork
Maintain a proper osmotic balance by pumping potassium into the
cell.
Removal to low salt regions will kill extreme halophiles—the bacteria
will lyse
glycoproteins of the cell wall comprised of aspartate and
glutamate –negatively charged amino acids whose negative
charge is shielded by the Na2+ in environment.
The Movie:: excerpt from “The Blue
Planet”
bacteria that live in the deep sea
extremely high salt
low pH
high pressure
extremely high heat
no sunlight
primary producers