6-3: Environmental effects on microbial growth Flashcards
What environmental factors 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
Increase rates of enzymatic reactions, but at a point proteins start to denature, membrane loses integrity
What happens at lower temperatures
Reactions proceed slowly, membrane fluidity becomes an issue, transport inefficient
Microbes with optimal growth rate below 15C
Psychrophile
Most widespread organisms, grow at intermediate temperatures
Mesophile
Microbes with optimal growth rate above 45C
Thermophile
Microbes with optimal growth rate above 80C
Hyperthermophile
Psychrophiles vs psychrotolerant
Psychrophiles grow optimally at low T, psychrotolerant organisms can grow at low T, but optimally as mesophiles
Psychrophiles live in
The oceans, arctic, the antarctic, glaciers
What happens when psychrophiles are exposed to moderate temperatures
They are killed
What adaptations do psychrophiles have
Increased short f.a. chain and unsaturated f.a. in cell membranes = fluidity
Cold shock proteins to help protein/RNA folding
Cryoprotectants to prevent ice formation
Where do thermophiles/hyperthermophiles live
Surface soils, compost piles in sunlight
Hot springs, hydrothermal vents
The only microbe that can grow at T above 60C
Prokaryotes
What microbe can grow up to 122C
Archaea
How are thermophiles/hyperthermophiles adapted to high temperatures
Longer more saturated f.a. hold membrane together (archaea have lipid monolayer)
Heat-stable enzymes/solutes
Microbes that prefer low pH (acidic conditions) are
Acidophiles
Microbes that prefer higher pH (alkaline conditions) are
Alkaliphiles
What are acid-tolerant organisms
Tolerate low pH, prefer neutral
Cytoplasmic pH in alkaliphiles and acidophiles is…
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 # needed to get sick), increasing stomach pH = lower infectious dose
What does high concentrations of solutes in the environment lead to
Water leaves cell = shrinking, dehydration
What does low concentrations of solutes in the environment lead to
Water flows into cell = bursts
What is the most significant osmotic factor
Salt concentrations
What are halophiles
Live in high salt environments, may require high concentrations
What are compatible solutes
Solutes produced by cell in high solute environments to increase cytoplasmic solute conc.
What are facultative anaerobes
O2 not required, but grow better with it
What are microaerophilic microbes
Excel in low O2 environments
Obligate anaerobes are…
Microbes that would die in the presence of O2
Some anoxic environments…
Sediments, bogs, marshes, animal intestinal tracts
Aerobic/aerotolerant organisms produce enzymes to detoxify what molecules
Reactive oxygen species (toxic) present when O2 is present
