3.4: Effect of Temp on Microbial Growth

Question 1

all organisms have 3 cardinal temperatures at which they grow, what are they?

Answer 1

• minimum
• optimum
• maximum

Question 2

what does temperature affect

Answer 2

• the rate of chemical reactions in the cell
• higher temp = faster reactions

Question 3

is optimum temperature normally closer to the maximum or minumum?

Answer 3

• maximum

Question 4

where do you put bacteria if you want them to live for a long time

Answer 4

• in the fridge > the membrane freezes and transport processes slow, they go into a dormant state

(like butter lipids in membrane solidify)

Question 5

why do we heat bacteria to kill them?

Answer 5

Because protein denaturation occurs at high temps, cytoplasmic membrane falls apart; thermal lysis

Question 6

what are psychrophiles? where are they found, what is their maximum temp, above what temp they die?

Answer 6

cold loving microbes, found only in permanently cold environments, their maximum temp is 20 C, above this they will die.

Question 7

what are mesophiles? where are they found, optimum temp? example?

Answer 7

• organisms that have midrange temp optima; found in:
  -soils and lakes (optimum temp ~30 C)
  -warm-blooded animals (optimum temp often 37 C)
  ex;* E. coli*

(midrange = temps humans like)

Question 8

how can psychrophiles grow below 0 degrees C, what’s an example location of where they can grow?

Answer 8

• in solid ice there are tiny pockets where solutes have lowered the freezing point of liquid water (could be microscopic but that’s all they need)
• antarctic sea ice, or frozen lakes

Question 9

even bacteria that spend all their time in ice often have optima above 0 degrees, why? what’s an example of a bacteria like this?

Answer 9

• as temp increases reaction rate increases so higher temp would still be more favorable for them
• ex: Polarmonas shows optimum growth at 4 degrees celsius

Question 10

what do psychrophiles have that make life in the cold possible?

Answer 10

• enzymes that function optimally at low temperatures
  -may denature at moderate temp
• modified lipids in the cytoplasmic membrane
  -high unsaturated fatty acid content
  -unsaturated fatty acids remain semi-fluid at lower temperatures.

Question 11

what’s the difference between saturated and unsaturated fatty acids?

Answer 11

• saturated: every carbon is holding as many H’s as it can, saturated with H. (straight, no double bond necessary)
• unsaturated: not as many H’s, so double bond between 2 carbons, phospholipid has a kink in one tail, so its more fluid.

Question 12

what are psychrotolerant optima, what’s unique about them?

Answer 12

• 20 C to 40 C, like mesophiles
• but can also grow slowly at 0 C
• more widely distributed in nature than true psychrophiles

Question 13

what’s an example of psychrotolerants?

Answer 13

• the bacteria that spoil food in your fridge
• we put food in fridge to slow growth of psychrotolerants, prevents food from spoiling as fast

Question 14

what are thermophiles optimum temp, where are they found, example?

Answer 14

• optimimum temp 45- 80 C
• found in hot springs, surface soils and compost, even in hot water tanks
• ex.* Thermus aquaticus* -source of heat stable enzymes

Question 15

why was* thermus aquaticus* important

Answer 15

Revolutionized bio and microbio, PCR relies on enzymes from this, very first PCR this

Question 16

what are hyperthermophiles, optimum temp, and where are they found and example?

Answer 16

• extreme heat loving
• optimum temp: above 80 C (or even above 100 C)
• found in boiling hot springs, and deep ocean hydrothermal vents
• ex: Methanopyrus kandleri -Hyperthermophilic Archaea

Question 17

what is the archaea that can live in the highest temp discovered

Answer 17

Methanopyrus kandleri -Hyperthermophilic Archaea can live in up to 122 C (higher than an autoclave 121)

Question 18

what are the upper temp limits for life?

Answer 18

• only prokaryotes can grow above ~65 C (no eukaryotes)
  -high prokaryotic diversity (both archaea and bacteria) can live in high temp
  -chemoorganotrophs and chemolithotrophs
  -no phototrophy above 73 C (no hyperthermophiles that are photosynthetic exist)
  -lab experiments with biomolecules suggest 140-150 C is the limit for life of prokaryotes (bc this temp breaks down ATP which all life need)

Question 19

what makes life possible at extremely high temperatures

Answer 19

• enzymes that are stable at high temp
• Modified lipids to maintain membrane fluidity
  -bacteria -more saturated fatty acids
  -archaea -tetraether lipids (monolayer membranes)
• Chaperonins (Heat shock proteins)
  -protect other proteins from denaturation and refold proteins that have already been damaged

Question 20

why are thermophiles of interest?

Answer 20

• thermophiles and hyperthermophiles produce enzymes widely used in the industry:
  -Taq DNA polymerase is used for in vitro DNA synthesis reactions, allows automation of the polymerase chain reaction (PCR) used to amplify DNA
  -Hydrolytic enzymes: proteases, cellulases, lipases
• Enzymes of thermophiles are more stable and tend to have higher activity than their mesophilic counterparts.

Question 21

where are hyperthermophilic archaea and bacteria found in a phylogenetic tree? what does this suggest?

Answer 21

• hyperthermophilic Archaea and Bacteria are found on the deepest, shortest branches of the phylogenetic tree
• on either side of LUCA -suggests LUCA was also a hyperthermophile

Question 22

the oxidation of what gas is common to many hyperthermophiles and may have been first energy-yielding metabolism

Answer 22

• H2
• H2 + O2 > 2H2O reaction gives off energy