Rhizobium
Why is nitrogen-fixation such a problem for animals?
Gaseous nitrogen (N2) is a triple bond N = N. This bond is hard to break.
All organisms rely on bacteria to fix nitrogen.
Rhizobium species fix nitrogen and convert N2 to NH3
N2
2NH3
N-fixing bacteria and plants live in close association in the nodules of plants.
Rhizobiums have a large enzyme complex called
nitrogenase
which catalyses the following reaction:
Nitrogenase is very sensitive to O2.
It only
operates under anaerobic conditions.
Plants provide this anaerobic environment.
How do plants provide this environment?
·Some plants contain hemoglobin leg.
·Leg hemoglobin is an O2-binding hemoglobin that gets rid of any extra
O2 hanging around.
·Plants isolate the bacteria from the soil.