2. NITROGEN FIXATION
Nitrogen fixation is the conversion of free nitrogen
into nitrogenous compounds to make it available
for absorption of plant.
Lawes and gilbert in 1891 showed that legumes
had the inherent ability to add nitrogen to the soil.
plays a major role in “global biological productivity
3. ROLE OF NITROGEN IN PLANT
• Growth of all organisms depends on the availability of mineral nutrients
• Essential component Of proteins, nucleic acids and other cellular constituents.
• Major substance in plant next to water
• Building block
• Play important role in metabolic growth, reproduction and heredity.
• Constituent of
Chlorophyll Protein
Alkaloids Vitamins
4. SOURCES
• ATMOSPHERIC NITROGEN
78% of atmosphere N2 is termed as dinitrogen.
This N2 is fixed (N2-> NH3) by bacteria called Diazotrophs,& phenomenon is
diazotrophy.
• NITRATES AND NITRITES AND AMMONIA
Nitrate(NO3) is a chief form.
Amino acid in the soil
• ORGANIC NITROGEN COMPOUND IN INSECTS
5. Types
The table below shows some estimates of the amount of N2 fixed on a global scale. Total bio
N2 fixation is estimated to be twice as much as the total N2 fixation by non-bio processes
6. NON-BIOLOGICAL
• It includes Haber’s process:
• This reaction takes places at high temperature 500°C and pressure of 4000
atms.
• Lightning and UV radiation cause the formation of nitrogen oxides.
• These gases reached in soil through rain or dew and total N2 input in soil.
• Reaction involved:
• N2 + O2
𝑳𝑰𝑮𝑯𝑻𝑵𝑰𝑵𝑮
.
> 2NO (nitric oxide)
• 2NO +O2
𝑶𝑿𝑰𝑫𝑨𝑻𝑰𝑶𝑵
.
> 2NO2
7. BIOLOGICAL FIXATION
FIXATION OF ATMOSPHERIC NITROGEN INTO NITROGENOUS SALTS WITH THE HELP OF
MICRO ORGANISMS. IT IS OF TWO TYPES:
It is a type of nitrogen fixation of
atmospheric nitrogen carried out by micro-
organisms like bacteria that are free living
in soil. Examples include:
Free living aerobic: Azotobacter,
Beijerenckia.
Free living anaerobic: Clostridium
• TWO MAIN STEPS OF NON-SYMBIOTIC N2
FIXA TION
1. AMMONIFICATION
2. NITRIFICATION
The fixation of atmospheric
nitrogen by microorganism living
symbiotically inside the plant roots
is called symbiotic nitrogen
fixation.
The system consists of bacteria of
the species rhizobium together with
many member of family
Leguminosae such as peas, beans
etc. to form nitrogen-fixing
cooperatives.
8. NON SYMBIOTIC
TWO MAIN STEPS OF NON-
SYMBIOTIC N2 FIXA TION
AMMONIFICATION – the conversion
of NH3 from natural nitrogen
compound(amino acid) by
microorganism.
NITRIFICATION – the conversion of
ammonium to nitrate. This is
Brought about by the nitrifying
bacteria, which are specialized to
gain their energy by oxidizing
ammonium, while using CO2 as
their source of carbon to
synthesize organic compounds.
9. SYMBIOTIC NITROGEN FIXATION
• LEGUME SYMBIOSES- The most familiar
examples of nitrogen-fixing
symbioses are
the root nodules of legumes (peas,
beans clover, etc.)
• Rhizobium forms nodules and
participate in the symbiotic
acquisition of nitrogen.
• If legumes are bigger partner and
rhizobia is a smaller such relationship
developed is named as micro
symbiosis and the strains are termed
as micro symbionts.
10. PROCESS OF ROOT NODULE FORMATION
• Rhizobia live freely as soon as they come in
contact with suitable host they starts the process
of infection.
• Polysaccharides on the surface of the bacteria bind
it’s to the lessons on the surface of the root.
• The factors for proteins located in the nodule are
called nodulins on bacterial surfaces named as
bactericidins which help in nodulation.
11. 1. CURLING AND DEFORMATION OF ROOT HAIRS.
• Invasion of
rhizobia occurs
through root
hairs.
12.
13. 2. FORMATION OF INFECTION THREAD AND
FORMATION OF NODULE.
The tip of curled root hair bends the bacteria
(rhizobial polysaccharides and DNA) penetrates
and grow in the form of an infection tube.
Meanwhile the polysaccharide reacts with the
component of root hair cell to form an “organizer”.
the organizer induces the production of
polygalacturonase (PG) followed by
depolymerization of cell wall pectin.
15. LEGHAEMOGLOBIN
• A red pigment similar to blood
haemoglobin is found in the
nodules between Bacteroides and
the membrane envelops
surrounding them.
• The function of this molecule in
nodules is to reduce the amount
of Free oxygen,
• thereby to protect the nitrogen-
fixing enzyme nitrogenase, which
is irreversibly inactivated by
oxygen
16. MECHANISM OF N2 FIXING MICRO ORGANISM
Enzyme complex
• Nitrogenase the process
of biological nitrogen
fixation is catalyzed by an
engine complex called
nitrogenase complex
• Three different forms of
nitrogenase
NITROGENASE
MOLYBDENUM
VANADIUM
IRON
17. STRUCTURE
• Dinitrogenase reductase (Fe-
protein) Azoferredoxin.
1. Smaller component
2. Fe-S Protein component
3. Extremely sensitive to oxygen an
inactivated by it
4. Dimer of two identical peptide
chains each with molecular weight
30-72 kDa (Depending on
microorganisms)
5. This dimer is bridged by 4(Fe-S)
cluster. That are 12 titrable thiol (-
SH ) group
• Dinitrogenase (Mo-Fe protein)
1. Larger component ( Mo-Fe protein)
2. site of nitrogen fixation
3. This component is also sensitive
to oxygen
4. Tetramer with two mixed peptide
chains (Alpha2beta2)
5. Total molecular mass 180-235
kDa(approx).
6. Nitrogenase contain 2Mo atoms,
about 24 labile S atoms and 30
titrable thiol groups.
18. PROPERTIES
• Nitrogenase is sensitive to oxygen hence biological nitrogen fixation requires
anaerobic conditions.
• Anaerobic Organism = OK
• Aerobic Organism nitrogen fixation Occurs when conditions are made to maintain
very low level of oxygen.
• Apart from nitrogen the engines nitrogenase can reduce a number of other
substrate example nitrous oxide (N2O) ,azide (N3- ), C2H2 (acetylene) ,protons (2H+)
and catalyze hydrolysis of ATP.
20. CONT.
The reduction of N2 is obligatorily linked to reduction
of two protons to form H2 molecule also as it is
necessary for binding of N2 at the active site.
The electrons and ATP are provided by
photosynthesis and respiration of the host.
In some rhizobia, hydrogenase enzyme is found which
splits H2 to electrons and protons thereby increase
the efficiency of N2 fixation.
21. BIBLIOGRAPHY
S.NO BOOKS
1. Textbook of MICROBIOBIOLOGY-by R.C DUBEY, D.K MAHESHWARI
2. Prescott’s microbiology(ninth edition)
WEBSITES
3. Nitrogen Fixation- WIKIPEDIA
4. https://courses.lumenlearning.com
Boundless microbiology Nitrogen Fixation
RESEARCH PAPER
5. Jim Deacon, Institute of Cell and Molecular Biology, The University of
Edinburg, the microbial world, the nitrogen cycle and nitrogen fixation.
