Lab 3 - Nitrogen fixing bacteria

Question 1

Why is nitrogen essential?

Answer 1

All living organisms require nitrogen to make amino acids, nucleotides and vitamins

Question 2

What are examples of microbes that fix nitrogen?

Answer 2

Rhizobium, Azospirillum, Azotobacter

Question 3

What is the component in mannitol media that limits the type of bacteria?

Answer 3

Mannitol as the sole carbon source and no nitrogen

Question 4

What bacteria were used as controls in this experiment?

Answer 4

Negative control = Bacillus cereus
Positive control = Azotobacter chroococcum

Question 5

What was the expected colony morphology on the NFMB?

Answer 5

Large and mucoid

Question 6

What was the expected morphology in the Gram stain?

Answer 6

Rod shaped vegetative cells and possible cysts larger and rounder than vegetative cells

Question 7

How did non-symbiotic nitrogen fixation occur in this experiment? Which of the control bacteria is an examples?

Answer 7

1. Reduce nitrogen to ammonia
2. Nitrification of ammonia to nitrite then nitrate
3. Denitrification of nitrate to nitrogen

Eg. Azotobacter (positive control) and

Question 8

Briefly describe the method used in this experiment

Answer 8

1. Add NFMB to Erlenmeyer flask
2. Add soil to Erlenmeyer flask
3. Incubate 1 week at room temperature
4. Streak loopfuls of NFMB culture onto NFMA plates
5. Incubate 1 week at room temperature

Question 9

Which control did the NFMB soil culture look like in terms of colonies?

Answer 9

Positive control = Azotobacter chroococcum