MIDTERM 2 - Indole and Catabolite Repression

Question 1

What is tryptophan metabolism a critical diagnostic for?

Answer 1

Distinguishing between Escherichia from other members of the Enterobacteriaceae

Question 2

Tryptone broth

Answer 2

Medium containing proteins digested with trypsin and rich with many amino acids especially tryptophan.

Question 3

What must bacteria do in order to metabolize tryptophan from the environment?

Answer 3

the bacteria must have a way to translocate the tryptophan into the cell

Question 4

What happens to tryptophan once it enters the cell?

Answer 4

Its hydrolyzed by tryptophanase.

2. this produces indole + ammonia + pyruvate
3. Indole and Ammonia results from removal of nitrogen in the amino acid
4. Pyruvate being part of the carbon backbone

Question 5

Out of the three products ammonia, pyruvate, and indole, which one is used for production of energy?

Answer 5

Pyruvate

Question 6

Where is tryptophanase production highest in?

Answer 6

Tryptophanase production and activity is highest in cells growing AEROBICALLY.

Question 7

True or False: is tryptophan metabolism a fermentative process?

Answer 7

False

Question 8

What can inhibit the pathway of tryptophanase

Answer 8

The presence of Glucose

Question 9

How is the inhibition of the tryptophanase pathway made possible

Answer 9

Through the inhibition of the production of alternative enzymes by an unknown catabolite of glucose metabolism (catabolite repression)

Question 10

What happens to indole in presence of glucose?

Answer 10

Level of indole production drops below detectable levels even for organisms capable of tryptophan metabolism

Question 11

How do you get optimal evaluations of the ability to produce indole?

Answer 11

1. Cultures grown aerobically in tryptone
2. No glucose in tryptone broth
3. Incubated at organisms preferred growth temp
4. for 48 hours

Question 12

What reagent do you add after incubating your organism in tryptone?

Answer 12

Kovacs Reagent

Question 13

What is kovacs reagent?

Answer 13

It contains

1. acidified p-DMAB and
2. Amyl Alcohol

Question 14

Significance of p-DMAB and its flaws?

Answer 14

It reacts with indole to produce a red-violet product called rosindole.
2. Unfortunately p-DMAB reacts with tryptophan as well to produce the same product. This gives rise to erroneous interpretation.

Question 15

Why is amyl Alcohol important in the Kovacs reagent?

Answer 15

it serves to separate the substrate tryptophan from the product indole

Question 16

Why is Amyle Alcohol suited for this test?

Answer 16

1. Indole is soluble in amyl alcohol but tryptophan is not
2. p-DMAB is soluble in it
3. Amyl alcohol is immiscible in water and therefore separates from it
4. Amyl alcohol is less dense than water and forms an easily visible layer on top of the aqueous culture medium

Question 17

Positive Reaction for Indole test?

Answer 17

Dark Red-Violet color in the amyl-alcohol layer on top of the broth

Question 18

Negative reaction for indole test?

Answer 18

Any color other than dark Red-violet (pink, Orange, Or Amber) in the amyl-alcohol layer on top of the broth.

Question 19

What does a red color in the broth layer mean?

Answer 19

it means tryptophan is still present