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 37 o C
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
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 39 o C (example: E. coli found in warm blooded animals, soil water in temperate or tropical zones) Thermophiles: high temperature optima circa 60 o C Extremophiles Psychrophiles: low temperature optima circa 4 o C Hyperthermophiles: extremely high temperature optima circa 88 o C or 106 o C
Psychrophiles: Microbial Growth at cold temperatures Grow in cold environments where the temperature is CONSISTENT Depths of the open ocean (1-3 o C) 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 20 o C to 40 o C 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 o C but have a temperature optima of 20-40 o C Soil and water in temperate climates Meat, dairy products and produce stored under refrigeration (4 o C) 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 helixBeta 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 42 o C to 68 o C) Compost piles (65 o C) Artificial environments Hot water heaters and electric power plants
Hyperthermophiles (temperature range 88 o C to 106 o C) Found in hot springs and geysers that have temperatures near boiling point (92 o C to 100 o C—depending on elevation)—Yellowstone Nat’l Park/ Wyoming Deep sea Hydrothermal vents (212 o C)/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 (H 2 S) oxidized into sulfuric Acid (H 2 SO 4 ) 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%)
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