Temperature and microbial growth

Question 1

What are cardinal temperatures?

Answer 1

Characteristic temperatures for any given microorganism

Question 2

Name and describe the cardinal temperatures.

Answer 2

• Optimum temperature: temperature at which growth is most accelerated
• Minimum temperature: below this temperature, no growth can occur
• Maximum temperature: above this temperature, no growth can occur

Question 3

What happens below minimum temperature?

Answer 3

	Cytoplasmic membrane gelling
•	Prevents energy generation because membrane can no longer pump protons
	Proteins no longer function
•	Membrane transport ceases
•	Metabolic enzymes no longer functional

Question 4

What happens above maximum temperature?

Answer 4

1) Key proteins are irreversibly denatured

2) Cytoplasmic membrane collapses (thermal lysis)

Question 5

What are the classes of microbes based on their optimal temperatures?

Answer 5

1) Psychrophile: “cold-loving”
 Temperature range: < 0 to about 12
 Found in constantly cold environments: poles, deep oceans, high altitude

2) Mesophile: “middle”
 Optimum is less than 50
 Temporal-tropical latitudes (aquatic and terrestiral; most mammal pathogens)

3) Thermophile: “heat-loving”
 Optimal: 40-70°C
 Found in unusually (but not scorching) hot environments
 E.g. hot tubs, hot water tanks

4) Hyperthermophile
 Very high temperature optimum
 2 types
i. Found in geothermally heated water surface
o Optimum less than 100°C (above there is only steam, which does not support life)
ii. Found in deep sea vents
o Optimum of about 90-115°C
o Water remains liquid because of high atmospheric pressure

Question 6

What limits growth at low temperatures?

Answer 6

 Cytoplasmic membrane gelling
 Protein function
 Hence these features are modified

Question 7

What categories of microorganisms live in the cold? How do they compare/differ?

Answer 7

• Psychrophile
   Found in constantly cold environments: deep oceans, polar regions, high altitude
   Cardinal temperatures
  –> Optimal: less than 0°C to about 15
  –> Maximum: less than 20
  –> Minimum: less than -5
   They die at room temperature
   In ice, there must be presence of liquid water
  –> At least microscopic pockets of water within the ice
• Psychrotolerant
   Cardinal temperatures
  –>Optimal: 20-40°C
  –> Minimum is less than 0°C
   Include mesophiles but not psychrophiles
   They have a much broader temperature range

Question 8

What are the necessary molecular adaptations for life in the cold?

Answer 8

A) Proteins must be structurally flexible

B) Cytoplasmic membrane modified to maintain fluidity at low temperatures

Question 9

Describe the major features of the proteins of organisms that live in the cold.

Answer 9

1. Increase in α-helices, which form flexible pendulum
   i. Less β-sheets in secondary structure which are rigid
2. Increase the % of polar amino acids
   i. Polar amino acids interact more readily with the surrounding water, making a more open and flexible protein
   ii. Decrease in hydrophobic amino acids; these interact with each other within the protein (“closing” it)

Question 10

Describe the main features of the cytoplasmic membrane of organisms that live in the cold.

Answer 10

1. Bacteria: more kinks introduced in the fatty acids of the phospholipid membrane
   i. Hence more C=C
2. Archaea: more C=C in the phytanyl terpenes

Question 11

What is the most important requirement of the environment that will define whether life is present or not?

Answer 11

The presence of liquid water
In very cold environments: microscopic pockets of water within the ice
In very hot environments: liquid water must be present –> can be present at a temperature above boiling point, depending on pressure

Question 12

What are the categories of microorganisms that live at high temperatures?

Answer 12

* Thermophile
	Optimum around 40-70°C
	Environments
	Terrestrial hot springs overflows
	Fermenting materials e.g. compost, silage
	Hot water heaters/hot tubs

• Hyperthermophile
   Optimum between 65°C and less or equal to 115°C
   Environments
   Within hot springs
   Around volcanic steam vents (fumaroles)
   Adjacent to hydrothermal vents

Question 13

What are the necessary adaptations for life at high temperatures?

Answer 13

A) Enzymes and cytoplasmic proteins

B) Cytoplasmic membrane

Question 14

Describe the enzyme and cytoplasmic proteins of organisms that live in very hot environments.

Answer 14

1. Increase in β-pleated sheets
2. Increase in hydrophobic amino acids
   i. Increases the stability of hydrophobic core
3. Increase in acidic and basic amino acids
   i. Creates salt bridges on the surface between polar amino acids

Question 15

Describe the cytoplasmic membrane of organisms that live in very hot environments.

Answer 15

1. Increase in hydrophobic interactions within the lipid bilayer
   i. Bacteria: increase in saturated fatty acids
   ii. Archaea: decrease in C=C terpene
    They also have diglycerol tetraether membrane
    The monolayer makes them more resistant to peeling because it is covalently linked (tail-to-tail linkage of phytanyl

Question 16

Why do hyperthermophiles tend to be archaea?

Answer 16

 Some have diglycerol tetraether membrane

 The monolayer makes them more resistant to peeling because it is covalently linked (tail-to-tail linkage of phytanyl)