Topic 4-L3 - Environmental effects on microbial growth

Question 1

Even with ample nutrients/energy,
microbes can only grow if other
environmental factors are suitable

Answer 1

environmental factors are suitable

Question 2

Higher temperatures:

Answer 2

increasing rates of enzymatic reactions, but at a

point, proteins start to denature, the membrane loses integrity, etc.

Question 3

Lower temperatures:

Answer 3

reactions proceed very slowly, membrane fluidity becomes an issue,
transport is inefficient, etc..

Question 4

At maximum temp,

Answer 4

Protein denature, collapse of the cytoplasmic memb, thermal lysis

Question 5

At minimum temp,

Answer 5

Memb. Gelling, transport processes so slow that growth cannot occur

Question 6

Mesophile:

Answer 6

Most commonly studied and widespread. Growth at intermediate temperatures (roughly the same temperatures as us)

Question 7

Mesophilic are typically organisms that

Answer 7

comprise microbiomes of animals. Pathogenic organisms – medically relevant

Question 8

To kill Salmonella in food, they need to be heated to

Answer 8

65-75oC for ~10 minutes

temperature the bacteria experience, not the temp of the oven

Question 9

Psychrophile:

Answer 9

Optimal growth rate < 15oC

Question 10

Where do Psychrophiles psychrotolerant microbes

Live?

Answer 10

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)

Question 11

Psychrophiles grow

Answer 11

optimally at low temperatures

Question 12

psychrotolerant organisms can grow at low temperatures, but

Answer 12

grow optimally as mesophiles (20-40oC)

Question 13

How to kill a psychrophile?

Answer 13

Expose to moderate temp

Question 14

Adaptations of psychrophiles

Answer 14

• 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

Question 15

Cold shock proteins

Answer 15

(present in non-psychrophiles as well) to help protein/RNA folding at low temperatures

Question 16

Cryoprotectants

Answer 16

such as anti-freeze proteins to prevent ice formation

Question 17

Unlike excessive heat, cold temperatures don’t always

Answer 17

kill other organisms, just prevent growth. Bacteria are commonly stored
at -80oC for years in a 10% glycerol (or 10% DMSO) solution

Question 18

Thermophile:

Answer 18

Optimal growth rate < 45oC

Question 19

Hyperthermophile:

Answer 19

Optimal growth rate > 80oC

Question 20

Environments where Thermophiles (and hyperthermophiles) can be found

Answer 20

• 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

Question 21

Only prokaryotes can thrive at

temperatures above

Answer 21

~60-65oC

Question 22

Wide range of optimal growth temp for

thermophiles/hyperthemophiles

Answer 22

• Certain bacteria can grow up to ~95oC

- Certain archaea can grow up to ~122oC

Question 23

Thermophiles (and hyperthermophiles): Adaptations to high temperature

Answer 23

• 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.

Question 24

Most microbes grow optimally at a ______ pH

Answer 24

neutral

Question 25

acidophiles

Answer 25

microbes that prefer low pH. Some are acid- tolerant but prefer neutral pH.

Question 26

alkaliphiles

Answer 26

prefer a pH >8, and as high as 10.

Question 27

cytoplasmic pH will

Answer 27

vary somewhat in alkaliphiles and acidophiles

Question 28

cytoplasmic pH is generally

Answer 28

maintained close to neutrality (pH 6-8)

Question 29

Low pH of stomach acid is an important barrier that protects us from

Answer 29

infection by consuming food/water contaminated with pathogenic microbes

Question 30

Acid tolerance of enteric pathogens has a big influence on

Answer 30

infectious dose

Question 31

infectious dose

Answer 31

(min. number of organisms consumed to become sick)

Question 32

The more acid tolerant, the

Answer 32

smaller the infectious dose required

Question 33

Halophiles live in high.. Extreme halophiles typically..

Answer 33

salt environments. requires high concentrations of salt – NaCl – in order to survive.

Question 34

They most significant osmotic factor in nature

Answer 34

Salt concentration

Question 35

Higher concentrations of solutes in environment (lower conc. of water) leads to water

Answer 35

leaving the cell – shrinking, dehydration

Question 36

Concentration of water (i.e. concentration of solutes dissolved in water) is another important

Answer 36

environmental factor

Question 37

A key strategy to grow in high solute | environments is to produce

Answer 37

high concentrations of solutes (increase cytoplasmic solute conc.)

Question 38

Compatible solutes are solutes produced to

Answer 38

increase conc. Of solutes inside cell – they do not interfere with cell’s biochemical processes (like KCl)

Question 39

Aerobes include

Answer 39

- obligate: NEED O2 - Facilutative: not needed, but better with O2 - Microearophilic: needed at lower levels

Question 40

Anaerobes include

Answer 40

Aerotolerant: not needed, and growth no better with O2 Obligate: O2 lethal

Question 41

anoxic environments on the planet:

Answer 41

many sediments, bogs, marshes, subsurface, animal intestinal tracts (microaerobic?)

Question 42

In anoxic env., O2 respiration provides

Answer 42

No advantage

Question 43

O2 is not reactive or toxic on its own, but in presence of

Answer 43

O2 reactive oxygen species are generated in all cells via reduction of O2. - Aerobic/aerotolerant organisms produce enzymes to detoxify these molecules.