Topic 4-L3 - Environmental effects on microbial growth Flashcards
Even with ample nutrients/energy,
microbes can only grow if other
environmental factors are suitable
environmental factors are suitable
Higher temperatures:
increasing rates of enzymatic reactions, but at a
point, proteins start to denature, the membrane loses integrity, etc.
Lower temperatures:
reactions proceed very slowly, membrane fluidity becomes an issue,
transport is inefficient, etc..
At maximum temp,
Protein denature, collapse of the cytoplasmic memb, thermal lysis
At minimum temp,
Memb. Gelling, transport processes so slow that growth cannot occur
Mesophile:
Most commonly studied and widespread. Growth at intermediate temperatures (roughly the same temperatures as us)
Mesophilic are typically organisms that
comprise microbiomes of animals. Pathogenic organisms – medically relevant
To kill Salmonella in food, they need to be heated to
65-75oC for ~10 minutes
temperature the bacteria experience, not the temp of the oven
Psychrophile:
Optimal growth rate < 15oC
Where do Psychrophiles psychrotolerant microbes
Live?
live in the Arctic, the Antarctic, within glaciers
- A lot of the earth is (what we would consider) cold. E.g. - oceans have an average temperature of 5oC (warmer at surface)
Psychrophiles grow
optimally at low temperatures
psychrotolerant organisms can grow at low temperatures, but
grow optimally as mesophiles (20-40oC)
How to kill a psychrophile?
Expose to moderate temp
Adaptations of psychrophiles
- Proteins have different structural features/elements to permit proper folding at low temperatures – fewer rigid structural elements to remain flexible
- Cell membranes have increased short chain fatty acids and unsaturated fatty acids (including polyunsaturated fatty acids) to allow it to remain fluid
- cold shock proteins
- cryoproteins
Cold shock proteins
(present in non-psychrophiles as well) to help protein/RNA folding at low temperatures
Cryoprotectants
such as anti-freeze proteins to prevent ice formation
Unlike excessive heat, cold temperatures don’t always
kill other organisms, just prevent growth. Bacteria are commonly stored
at -80oC for years in a 10% glycerol (or 10% DMSO) solution
Thermophile:
Optimal growth rate < 45oC
Hyperthermophile:
Optimal growth rate > 80oC
Environments where Thermophiles (and hyperthermophiles) can be found
- Surface soils (directly exposed to sunlight), compost piles can reach
temperatures of up to 70oC! - Hot springs and hydrothermal vents are
also hot spots for thermophiles
Only prokaryotes can thrive at
temperatures above
~60-65oC
Wide range of optimal growth temp for
thermophiles/hyperthemophiles
- Certain bacteria can grow up to ~95oC
- Certain archaea can grow up to ~122oC
Thermophiles (and hyperthermophiles): Adaptations to high temperature
- Protein structure adjustments, increased numbers and strength of intramolecular interactions
- Heat-stabilizing solutes are produced to high levels to help support protein structure
- heat-stable enzymes. PCR requires a heat stable DNA polymerase.
- longer fatty acids and more saturated - archaea use the lipid monolayer to hold memb. Together at very high temps.
Most microbes grow optimally at a ______ pH
neutral
acidophiles
microbes that prefer low pH. Some are acid- tolerant but prefer neutral pH.
alkaliphiles
prefer a pH >8, and as high as 10.
cytoplasmic pH will
vary somewhat in alkaliphiles and acidophiles
cytoplasmic pH is generally
maintained close to neutrality (pH 6-8)
Low pH of stomach acid is an important barrier that protects us from
infection by consuming food/water contaminated with pathogenic microbes
Acid tolerance of enteric pathogens has a big influence on
infectious dose
infectious dose
(min. number of organisms consumed to become sick)
The more acid tolerant, the
smaller the infectious dose required
Halophiles live in high..
Extreme halophiles typically..
salt environments.
requires high concentrations of salt – NaCl – in order to survive.
They most significant osmotic factor in nature
Salt concentration
Higher concentrations of solutes in environment (lower conc. of water)
leads to water
leaving the cell – shrinking, dehydration
Concentration of water (i.e. concentration of solutes dissolved in water) is another important
environmental factor
A key strategy to grow in high solute
environments is to produce
high concentrations of solutes (increase cytoplasmic solute conc.)
Compatible solutes are solutes produced to
increase conc. Of solutes inside cell – they do not interfere with cell’s biochemical processes (like KCl)
Aerobes include
- obligate: NEED O2
- Facilutative: not needed, but better with O2
- Microearophilic: needed at lower levels
Anaerobes include
Aerotolerant: not needed, and growth no better with O2
Obligate: O2 lethal
anoxic environments on the planet:
many sediments, bogs, marshes, subsurface, animal intestinal tracts (microaerobic?)
In anoxic env., O2 respiration provides
No advantage
O2 is not reactive or toxic on its own, but in presence of
O2 reactive oxygen species are generated in all cells via reduction of O2.
- Aerobic/aerotolerant organisms produce enzymes to detoxify these
molecules.
