This document discusses two types of nitrogen-fixing bacteria - Azotobacter and Azospirillum. Azotobacter is an aerobic, soil-dwelling bacteria that helps fix nitrogen. It is found in the rhizosphere of crops like rice and maize. Azospirillum is a microaerophilic, rod-shaped bacteria that colonizes plant surfaces and secretes plant hormones and nutrients to promote plant growth. Both bacteria play important roles in agriculture by increasing soil fertility and stimulating plant growth.

1. FREE LIVING AND
SYMBIOTIC NITROGEN
FIXERS
I PG MICROBIOLOGY
SRCW
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NITROGEN FIXING BACTERIA

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AZOTOBACTER

5. 1
• Nitrogen – basis of
amino acids,
proteins,
hormones and
many vitamins
2
• Conversion of
atmospheric
nitrogen gas to
fixed nitrogen
(inorganic –
ammonia)-
Nitrogen Fixation
3
• Reduction of
atmospheric
nitrogen by living
organisms –
Biological
nitrogen fixation
INTRODUCTION
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6. NITROGEN
FIXING BACTERIA
SYMBIOTIC
AZOSPIRILLUM
RHIZOBIUM
FRANKIA
NON -
SYMBIOTIC
ANABAENA
NOSTOC
TYPES
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7. AZOTOBACTER
Heterotrophic, naturally occurring, nitrogen fixing bacterium.
Found in neutral or alkaline soil.
Eg: Azotobacter chrococcum & Azotobacter beijerinckii –
important species.
Helps the plant in fixing nitrogen.
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8. Converts – N2
to Ammonia
Found in
rhizosphere of
crops – rice,
maize,
sugarcane,
vegetables
Seeds
inoculated with
Azotobacter –
aid uptake of
nutrients (N, P)
in wheat
They have the
potential to
improve plant
nutrition
AZOTOBACTER
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AZOTOBACTER BIOFERTILIZER USES
It is crucial to remember that azotobacter biofertilizer uses have shown that
they are of tremendous help in ensuring plant health.
The azotobacter is widely used in agriculture to increase soil fertility and
stimulate plant growth.
The presence of azotobacter is prominent in biofertilizers.
They are also crucial in the manufacture of alginic acid that is renowned
in medicine as an antacid.
It is also essential to highlight that azotobacter is critical to the food
industry as well.

10. AZOTOBACTER - CHARACTERISTICS
1
• Highly efficient for plant health
2
• Rod shape
• Gram negative bacteria
3
• Has flagellum
4
• Survive in harsh conditions – by forming
cysts
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AZOSPIRILLUM
Azospirillum is a plant growth-promoting diazotroph.
It is a free-living, gram-negative bacteria.
They are rod shaped and do not produce spores.
They are microaerophilic, i.e., they are aerobic but can survive
under low oxygen conditions as well.
They are found in freshwater and in close association with plant
roots in soil habitats. It is the plant growth-promoting bacteria
(PGPB)

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•They secrete plant hormones that make the root grow more branches
and root hairs.
•It makes nutrients such as nitrogen and phosphorus more available to
the plants.
•It also produces antioxidants that protect the plants in stressful
conditions.
•It competes with disease-causing microbes, making the plant less
susceptible to diseases.
CHARACTERISTICS

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AZOSPIRILLUM
MODE OF ACTION

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Azotobacter Azospirillum
Description
Azotobacter is an aerobic, soil-dwelling bacteria. Azospirillum is microaerophilic and surface colonising bacteria.
Oxygen Requirement
They are aerobic bacteria and require high oxygen concentration for
them to function.
They are aerobic, but are also microaerophilic and can survive in low
oxygen conditions.
Shape of Bacteria
Oval or spherical shape. Oblong-rod shaped.
Formation of Cysts
They form cysts to protect themselves from harsh environmental
conditions.
No formation of cysts.
Functions
It functions mainly as a nitrogen fixer, also useful in the production
of biofertilisers and biopolymers.
It is mainly useful as a plant growth-promoting bacteria.
Family of the Bacteria
Pseudomonadaceae Azospirillaceae
Temperature for Growth
20°C to 30°C 5°C to 42°C
DIFFERENCE

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