Microbial Tools for Nitrogen Aquisition

Question 1

What are the 5 main processes of the nitrogen cycle?

Answer 1

Inputs and outputs:
- Nitrogen fixation (nitrogen gas to ammonia. N2 -> NH3)
- Denitrification (nitrate to nitrite to nitrogen oxide to nitrogen gas. NO3-> NO2 -> N2O -> N2)
- Annamox (anaerobic ammonia oxidation, NH3 -> N2)

In the soil:
- Nitrification (ammonium to nitrites to nitrate. NH4 -> NO2 -> NO3)
- DNRA: dissimilatory nitrate reduction to ammonium. (nitrate to nitrite to ammonium and nitrous oxide. NO3-> NO2 -> NH4 + N2O)

Question 2

What are diazotrophs?

Answer 2

Nitrogen fixers
Depend on nitrogenase
Fix nitrogen in return for C and shelter from the plant.

Question 3

How much ATP is needed for 1 molecule of ammonia to be fixed?

Answer 3

16 ATP

Question 4

How is denitrification carried out?

Answer 4

Carried out by bacteria and fungi, respiration using N2O instead of CO2.
NO3 -> NO2 -> N2O -> N2
nitrate -> nitrite -> nitrous oxide -> nitrogen gas

Question 5

What is DNRA?

Answer 5

dissimilatory nitrite reduction of ammonium
competes with denitrification for nitrates.
produced N2O as biproducts
NO3 -> NO2 -> NH4 + N2O

Question 6

What are the 4 microbial functions to reduce dependence on N fertiliser?

Answer 6

1. Reducing N loss
   Reduce denitrification, increase DNRA instead of denitrification.
2. Enhancing N fixation
   Grow more legumes, more crops associated with diazotrophs.
3. Engineering new N fixing symbioses
   N fixing on roots, introducing azosrhizobium nitroenase activity.
4. Engineering new N fixing crops
   Cut out middle man (bacteria), needs to be anaerobic for nitrogenase. Mitochondria- low O2 but hard to engineer. Chloroplast- high O2 but hard to engineer

Question 7

What are negatives of diazotrophs?

Answer 7

Very sensitive to N and environmental conditions.
Sometimes use own NH3 produced instead of giving it to plants.