Reduction Of Nitrate Pg.97-98

Question 1

Some facultative and obligate anaerobes can substitute nitrate (NO3-) for oxygen (O2) as the final electron acceptor during cellular respiration, enabling them to grow without ____.

Answer 1

O2

Question 2

How do we test for the presence of nitrite?

Answer 2

By adding the nitrate reagents sulfanilic acid and dimethyl-alpha-naphthylamine (DAN).

Question 3

If the bacteria reduced nitrate (NO3-) to nitrite (NO2-), what color develops indicating the presence of nitrite (NO2-)?

Answer 3

A red color develops

Question 4

If there is no nitrite in the broth, what are the three explanations for its absence?

Answer 4

1. Bacteria does not reduce nitrate (- for nitrate reduction)
2. The bacteria reduce nitrate to nitrite and further reduce nitrite to ammonia (NH3)
   (+ for nitrate reduction)
3. The bacteria reduce nitrate to nitrite and further reduce nitrite to nitrogen gas (N2)
   (+ for nitrate reduction)

Question 5

Why are explanations 2 and 3, simply testing a nitrate broth culture for the presence off nitrite, not enough to determine if nitrate reduction has occurred?

Answer 5

Because nitrate may have been further reduced.

Question 6

Microbiologists add ______ and ______ that reduces nitrate to nitrite, if there’s still nitrate present.

Answer 6

Zinc and inorganic catalysts

Question 7

What does it mean when if there’s still nitrate present?

Answer 7

Then the bacteria did not reduce the nitrate.

Question 8

Zinc will react w the still present nitrate to reduce it
This is a - result because:

Answer 8

To nitrite.
Because zinc reduced the nitrate - not the organisms enzymes.

Question 9

Procedure: what are the two nitrate broths inoculated with?

Answer 9

B.spizizenii (subtilis) & A.faecalis
Incubate at 37 degrees Celsius for 3-4 days

Question 10

After incubation, what/how much is added to the nitrate broth culture?

Answer 10

5 drops of sulfanilamide acid and 5 drops of DAN

Question 11

-A red color indicates ______1.______ has occurred.
-No color change (inconclusive) must be confirmed by adding _______2.__________:
-If the color turns Red,___________3._____
-If there’s no color,___________4.__________

Answer 11

1.nitrate reduction
2. A pinch of zinc dust:
Red———> test is -
No color ———> test is + for nitrate reduction (bacteria reduced nitrate completely to NH3 or N2)

Question 12

Why is it negative for nitrate reduction if it turns red after zinc is added?

Answer 12

Because nitrate was reduced by zinc

Question 13

With what substrate are the nitrate reagents reacting?

Answer 13

Nitrite

Question 14

With what substance is the zinc reacting?

Answer 14

Nitrate

Question 15

What does the red color indicate?

Answer 15

Nitrite is present