Bacterial GrowthUnusual Growth Conditions

Microbial Diversity

Parameters other than nutrition that affect bacterial growth

1. pH—optimum pH of most organisms is 7.02. Water activity—most bacteria require a water activity between 0.9 and 1.03. 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 require5. Temperature—most organisms like 37oC

Cardinal TemperaturesThe temperatures ranging from minimum to maximum that allow for bacterial growth.

Minimum temperature: the lowest temperature at which an organismcan grow—lower temperatures do not support bacterial growth

Maximum temperature: the highest temperature at which an organismcan 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 organismfor 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 areunfrozen 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 optimaof 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 bacterialgrowth.

Molecular considerations: How do psychrophiles live in extremely cold environments?

Lipid and protein composition Proteins are active at cold temps and easily denatured at moderatetemperatures due to their secondary structure

Alpha helix Beta sheet>>>

Beta sheet structures are more rigid than alpha helical structures: proteinsconsisting predominantly of alpha helices are more flexibleCaveat: 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 arehigher in polar AA content and lower in hydrophobic AAcontent than in mesophiles—greater flexibility

Polar amino acids tend to interact with the surroundingaqueous environment while hydrophobic amino acidstend 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 environmentsHot 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’lPark/ Wyoming

Deep sea Hydrothermal vents (212oC)/primary food source

How to study hyperthermophilesimmerse microscope slides in hot springs/collect organisms

grow bacteria in pressurized vessels that reach temperaturesabove boiling point.

Molecular considerations: How do hyperthermophiles live in extremely hot

environments/Proteins

Amino acid composition and higher order structure of hyperthermophilesnot much different from that of mesophiles

Synthesize solutes within the cytoplasm that interact with the proteinsand 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 hyperthermophillicarchaebacteria consist of long (C-40) carbon chains with repeatingunits of isoprene sidechains

Isoprene

Specialized lipids of archaebacteria

The cytoplasmic membrane of hyperthermophilic archaebacteriacan be made up of lipid MONOLAYERS

Microbial growth at extreme pHAcidophiles: 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 dissolvesand cells lyse.

Alkaliphiles: organisms that grow best at high (alkaline) pHHighly basic environments such as soda lakes (Lake Hamara/Egypt) surrounding rocks rich in carbonate thatleaches into lake increasing the pH to 11.0

**these pH’s refer to the pH that the cells can GROW in, the pH of thecytoplasmic compartment must be within the range of 4.5 – 9.5 to maintain theIntegrity 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 evenmoderate levels of Na

Halotolerant: (St. aureus) can tolerate a reduction in Aw, but prefersTo grow in an environment where Na has not been added

Halophiles: prefers or needs to have Na in the environmentmild 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 bacteriawill lyse

glycoproteins of the cell wall comprised of aspartate and glutamate –negatively charged amino acids whose negativecharge is shielded by the Na2+ in environment.

The Movie:: excerpt from “The Blue Planet”

bacteria that live in the deep seaextremely high salt

low pHhigh pressure

extremely high heat

no sunlight primary producers