NITROGEN
METABOLISM
FIXATION
Submited by- Anjali
Rai
MSc (P) Biotechnology
NITROGEN METABOLISM
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Nitrogen Fixation can be defined as the
conversion of molecular nitrogen into
fixed form of nitrogen to make it
available for absorption by plants.
It is the third most important process
after respiration and photosynthesis.
It is essential for all living organisms.
CLASSIFICATION
NITROGEN FIXATION
NON-BIOLOGICAL
SYMBIOTIC
BIOLOGICAL
NON-SYMBIOTIC
BIOLOGICAL N2 FIXATION
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Conversion of elemental nitrogen or
gaseous nitrogen into nitrogenous
compounds or salts by certain
microorganisms like bacteria ,blue green
algae, fungi etc. is called biological
nitrogen fixation.
It is carried by two types of microorganisms. Eg Symbiotic and nonsymbiotic.
NON-SYMBIOTIC N2 FIXATION
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The Fixation of free nitrogen of the soil
by all those micro-organisms living freely
or outside the cell is called as nonsymbiotic biological N2 fixation.
NON-SYMBIOTIC N2 FIXATION
SYMBIOTIC N2 FIXATION
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The Fixation of free nitrogen of the soil
by microorganisms living symbiotically
inside the plant, is called as symbiotic
biological N2-fixation.
The term “symbiosis” is coined by De
bary in 1879.
CLASSIFICATION
1.
2.
3.
Nitrogen Fixation Through Nodule
Formation in Leguminous plants.
N2 Fixation through Nodule
formation in Non-leguminous
Plants.
N2-Fixation through NonNodulation.
The Nodulation process
The Nodulation process
The Nodulation process
The Nodulation process
The Nodulation process
N2-FIXATION IN NONLEGUMINACEOUS PLANTS
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In addition to legumes, there are many plants
specially trees and shrubs belonging to families
other than Leguminosae which produce rootnodules.
EgCasuarina- Frankia
Alnus- Frankia
Myrica- Frankia
Parasponia- Rhizobium
N2 Fixation through Nonnodulation
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It includes those plants where root
nodules are not formed but symbiotic N2fixation takes place.
ExamplesLichens - associated with fungi and algae
Azolla- Anabaena azollae.
Cycas –Anabaena or Nostoc
Gunnera macrophylla- Nostoc
Associative Symbiotic N2Fixation
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When the bacteria live in close association with
the roots of cereals and grasses and fix
nitrogen than the association is of loose
mutualism type and is called associative
symbiosis whereas this nitrogen Fixation is
called associative symbiotic nitrogen
fixation.
ExamplesAzotobactor paspali – Associated with Paspalum
notatum
Azospirillum brasilense- Cereal roots
Beijerinckia- Sugarcane roots
Cross-inoculation group
LEGHEMOGLOBIN
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The red pigment of the nodules is called
leg-hemoglobin and appears to be a
product of the Rhizoboium-legume
complex.
The pigment is not present in either
organism grown alone.
It is a reddish pigment found in the
cytoplasm of host cells.
It is an oxygen carrier & an efficient O2
scavenger
NON BIOLOGICAL N2 FIXATION
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1.
2.
Non biological N2 fixation is usually
found in rainy seasons during
lightening, thunder, storms and
atmoshpheric pollution.
It is of two typesPhysical
Chemical
NON- BIOLOGICAL n2 fIXATION
(PHYSICAL )
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1.
(PHYSICAL)N2 + O2
Lightening
2NO
Thunder (Nitric Oxide)
2. 2NO + O2
3.
2No2
Oxidation 2No2
(Nitrogen Peroxide)
+ Rain water
HNO2 + Hno3
NON- BIOLOGICAL n2 fIXATION (
CHEMICAL)
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(CHEMICAL)-
Haber’s Process
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N2 (g) + 3H2 (g)
2NH3 (g)
(g) H = -22 Kcal
By using a temperature of about
500 C and a pressure of about 1000
atm, there is about 50% conversion
of N2 to NH3
BIOCHEMISTRY OF NITROGEN
FIXATION
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Nitrogenase Complex- Key
Enzyme In N2 – Fixation.
Overall Reaction
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N2 + 8H+ + 8e- + 16ATP
+ 16ADP + 16Pi + H2
2NH4+
STRUCTURE OF NITROGENASE Fe
Protein
Assimilatory nitrate reduction
Schematic diagram of
nitrogenase complex
Electrons from
Reduced ferredoxin
Dinitrogenase Reductase
(Fe-Protein)
ATP
ADP
Dinitrogenase Reductase
( MO -Fe-Protein)
NH4+
N2
Reduction
8 e8 Ferridoxin or 8
Flavodoxin (oxidized)
8 Ferridoxin or 8
Flavodoxin (reduced)
8 e-
8 Dinitrogenase reductase
(oxidised)
8 Dinitrogenase reductase
(reduced)
16 ADP+ 16Pi
16 ATP
8 Dinitrogenase reductase
(reduced) + 16 ATP
8 e-
8 Dinitrogenase reductase
(oxidised)
MECHANISM OF NITROGENASE
REDUCTION
8 Dinitrogenase
(oxidized)
2NH4+
8 Dinitrogenase
(reduced)
8 eN2
NITROGENASE COMPLEX
ACTIVITY
1.
2.
3.
4.
5.
Nitrogenase the cardinal enzyme process.
A strong reductant such as, Ferredoxin or
flavodoxin or NADPH etc.
ATP
Presence of hydrogenase enzyme.
A system for regulation of the rate of the
NH3 production and one for assimilation
since biosynthesis of the nitrogenase
complex ceases when ammonia accumulate.
6. Protection of the nitrogen fixation
system from molecular oxygen which
inactivates nitrogenase and competes
for reductant.
7. Coenzymes and co-factor like TPP Co-A
inorganic phosphate Pi, and Mg+2.
8. The hydrogen releasing system or
electron donor which is usually pyruvic
acid but may also be glucose or sucrose
in some instances.
NITROGEN
CYCLE
Genetics of N2 Fixing
Microorganisms
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Genes responsible for N2 Fixation
are known as nif-genes while for
nodulation are called nod genes.
Nif genes have been isolated from
symbiotic bacteria Rhizobium
leguminosarium & free living N2
Fixing bacteria Klebsiella
pneumoniae
Nif GENES
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In Klebsiella pneumoniae Nif genes
are present which consists of 17
genes.
Distributed into 7 or 8 oparons.
Nif genes is regulated by NifA,NifL
genes.
In cyanobacteria there are other
Nif genes ie,Nif H,Dand K and Nif S
and Nif B.
NOD GENES
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Nod genes are present on symplasmid.
These genes are host specific
Regulation of nod genes is controlled
by Nod D genes.
The common Nod A,B,C genes are
conserved among rhizobium and
inactivation of these genes completely
depends on root hair infection and
nodule formation.
CONCLUSION
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N2 Fixing microorganisms (freeliving and symbiotic) are known as
diazotrophs.
Biological and non-biological N2
fixation.
Genetics of nitrogenase enzyme.
Presence of leghemoglobin.
Regulation of nitrogenase enzyme.