6-3: Environmental effects on microbial growth Flashcards
What environmental factors that need to be suitable for microbial growth
Temperature, pH, water, osmolarity, O2 levels, radiation levels, lack of toxic substances
All organisms have ________,_________ and _________ temperatures for growth
Minimal, optimal, maximal
What do higher temperatures do to microbial growth?
Increase rates of enzymatic reactions, but at a point proteins start to denature, membrane loses integrity
What do lower temperatures do to microbial growth?
Reactions proceed slowly, membrane fluidity becomes an issue, transport inefficient
What is the typical growth range for a microbe?
Less than 40 degrees C
What microbes have an optimal growth rate below 15C?
Psychrophile
What microbes have the most widespread organisms, grow at intermediate temperatures (8 to 48 degrees C)?
Mesophile
What do you call microbes with optimal growth rate above 45 degrees C?
Thermophile
What do you call microbes with optimal growth rate above 80C?
Hyperthermophile
What are psychrophiles?
Psychrophiles grow optimally at low temperatures
eg. Snow algae, Chlamydomonas nivalis
What are psychrotolerant organisms?
Can grow at low temperatures, but grrow optimally as mesophiles (20-40 degrees C)
Where do psychrophiles live?
The oceans, arctic, the antarctic, glaciers (areas that are always cold)
What happens when psychrophiles are exposed to moderate temperatures
They are killed
What adaptations do psychrophiles have
Increased short fatty acid chains and unsaturated fatty acids in cell membranes = fluidity
Cold shock proteins to help protein/RNA folding
Cryoprotectants to prevent ice formation
What do cold temperatures do to bacteria, compared to excessive heat?
Cold doesn’t always kill, unlike excessive heat. Actually prevents growth (eg. storing bacteria in 10% glycerol at -80)
Where do thermophiles/hyperthermophiles live
Surface soils, compost piles in sunlight
Hot springs, hydrothermal vents
What is the only domain of microbe that can grow at temperatures above 60C?
Prokaryotes
What temperature can bacteria grow up to? What temperature can archaea grow up to?
Bacteria - 95 degrees
Archaea - 122 degrees
How are thermophiles/hyperthermophiles adapted to high temperatures
Increased number and strength of intermolecular protein interaction
Heat stable solutes that support proteins
Longer more saturated f.a. hold membrane together (archaea have lipid monolayer)
Heat-stable enzymes/solutes (eg. Taq pol)
What are acidophiles?
Microbes that prefer low pH (acidic conditions)
What are alkaliphiles?
Microbes that prefer higher pH (alkaline conditions)
What is the cytoplasmic pH in alkaliphiles and acidophiles?
Maintained close to neutral (6-8)
What is the point of the low pH of the stomach?
Barrier that protects us from infection by consuming contaminated food/water
What does acid tolerance of enteric pathogens influence?
Infectious dose (minimum number of organisms needed to get sick), Buffering or increasing stomach pH = lower infectious dose
What is the most significant osmotic factor?
Salt concentrations
What are halophiles
Organisms that live in high salt environments (eg. hypersalinated lakes), may require high salt concentrations
What are compatible solutes
Solutes produced by cell in high solute environments to increase cytoplasmic solute concentration. Do not interfere with the cell’s biochemical processes (highly water soluble and inert).
List some common cytoplasmic compatible solutes
Glu/Pro, Sucrose, KCl, Glycerol
What are facultative anaerobes
O2 not required, but grow better with it. Use aerobic and anaerobic respiration.
What are microaerophilic microbes
Excel in low O2 environments, use aerobic respiration
Give some examples of anoxic environments.
Sediments, bogs, marshes, subsurface, animal intestinal tracts (microaerobic)
What are obligate anaerobes?
Microbes that would die in the presence of O2
Why is oxygen toxic to obligate anaerobes?
Can produce reactive oxygen species (toxic). Aerobic/aerotolerant organisms can detoxify these molecules.
