Microbial interactions are ubiquitous, diverse, critically important in the function of any biological community. The most common cooperative interactions seen in microbial systems are mutually beneficial. The interactions between the two populations are classified according to whether both populations and one of them benefit from the associations, or one or both populations are negatively affected.

1. DR. RACHANA CHOUDHARY
ASSTT.PROF. DEPARTMENT OF MICROBIOLOGY

2. CONTENTS
Introduction
History
Difference Between Symbiosis & Mutualism
Types
(A). Positive Interaction
(B). Negative Interaction
Conclusion
References

3. INTRODUCTION
•Many microbial populations interact and
establish associations with each other and with
higher organisms.
• The inter- and intra-relationships between
various microorganisms. This can include both
positive and negative interactions.
•They are ubiquitous, diverse and critically
important in the function of any biological
community.

4. HISTORY
• In 1879, de Bary coined the term Symbiosis to
describe any situation where two different
organisms live together.
• In 1964, Hamilton described interaction as
indirect interaction.
• In 1971, Odom divided all symbiotic
relationship into 2 groups
 Positive interaction.
Negative interaction.

5. DIFFERENCE BETWEEN SYMBIOSISAND MUTUALISM
Ecologists sometimes use the terms “mutualism” and
“symbiosis” interchangeably.
The word Symbiosis literally means “living together” .
Symbiosis is an ecological interaction between at least two
species (=partners) where there is persistent contact
between the partners.
Mutualism is an ecological interaction between at least
two species (=partners) where both partners benefit from
the relationship.
All mutual relationships are symbiotic relationships, but
not all symbiotic relationships are mutual relationships.

6. TYPES OF MICROBIAL INTERACTIONS

7. TYPES OF MICROBIAL INTERACTIONS

9. .
POSITIVE INTERACTION
(A)MUTUALISM
•Mutualism describes a relationship in which both
associated partners derive some benefit, often a vital
one from their living together.
•Mutualism is the way wear
two organisms of different species exist in a
relationship in which each individual benefits from
the activity of the other.
•Similar interactions within a species are known
as co-operation.
•It is highly specific and obligatory interactions.

10. EXAMPLES OF MUTUALISM
• Rhizobium-legume association
• Mycorrhizae
• Lichens
• Herbivore-Microbial interaction
• Clown fish and sea anemone

11. RHIZOBIUM-LEGUME ASSOCIATION

12. MYCORRHIZAE
It represents a mutualistic relationship between
the root system of higher plants and fungal
hyphae.
Classification of Mycorrhizae
Ectomycorrhizae
Endoomycorrhizae
Ectendomycorrhizae

13. ECTOMYCORRHIZAE
• They are common on many forest trees like pines, beech
etc. the fungal hyphae form a sheath over the outside of
the roots which is called ‘mantle of hyphae’.
• From this mantle, a hyphal network called hartignet
extends into the first few layers of the cortex and then
reaches the endodermis.
• common ectomycorrhizal genera are of Basidiomycetes
such as Amanita, Tricholoma.etc
• The fungi of this secrete various growth promoting
substances such as auxins, cytokines and gibberellin
acids. It also protect the host plant against soil borne
pathogens. Fungi derive their carbon from host(glucose,
fructose) and convert to mannitol.

14. ENDOMYCORRHIZAE
The mycorrhizae in which the fungal hyphae
invade the root cells without forming any external
sheath, mantle of hyphae are called endotropic
mycorrhizae.
Types of Endomycorrhizae
•Vesicular arbuscular (VA) Mycorrhizae.
•Orchidaceous mycorrhizae.
•Ericaceous mycorrhizae.

17. ECTENDOMYCORRHIZAE
It bears the characteristic of both ecto and endo
mycorrhizae.The fungal partner establishes mantle of
hyphae on the surface of root as well as hypal coils and
haustoria within the invaded cortical cells of root.
Examples-
‘Conifer-boletus-monotropa’ association . monotropa
usually grows near the roots of conifer in the forests. The
fungus called boletus forms a common mycorrhizal
association between conifer and monotropa.
Boletus forms ectomycorrhiaz with monotropa and
endomycorrhiza with conifer.

18. LICHENS
• Lichens are a complex life form that is a symbiotic
partnership of two separate organisms, a fungus and
an alga.
• The dominant partner is the fungus (Mycobiont),
which gives the lichen the majority of its
characteristics, from its thallus shape to its fruiting
bodies.
• The alga(Phycobiont) can be either a green alga or a
blue-green alga, otherwise known as cyanobacteria.
Many lichens will have both types of algae.
• There are approximately 3,600 species of lichens

19. TYPES OF LICHENS
The four main types of lichen thallus.
1. Crustose (Crustaceous) Lichens
2. Foliose (Foliaceous) Lichens
3. Fruticose Lichens
4. Squamulose Lichens.

20. TYPES OF LICHENS

21. HERBIVORE-MICROBIAL INTERACTION

22. clownfish & sea anemones

23. (B)COMMENSALISM
•It represents a relationship between two microbial
populations in which one is benefited and the other
remains unaffected (neither harm nor benefited). It is
unidirectional relationship between species.
•Example- A disease causing microbial population
when opens a lesions on host, it creates an entry
passage for other microbial population. Mycobacterium
leprae, cause leprosy opens lesion on the body surface
and allow other pathogens to establish secondary
infections.

24. EXAMPLE OF COMMENSALISM

25. (C)PROTO-COPERATION(SYNERGISM)
• It is association between two microbial populations in which
both populations benefit from each other. it allows
populations to perform metabolic activities i.e. involving the
exchange of nutrients b/w two species, a phenomenon called
syntrophism.
• In which both populations benefits from each other, but it
differs from the mutualism in that the association is not
‘obligatory’.
• The Desulfovibrio bacteria supply hydrogen sulphide and
carbon dioxide to Chlorobium bavteria and in turn the
Chlorobium make sulphate and organic material available to
Desulfovibrio. Thus mixture of two populations produce
more cellular material than either alone.

26. NEGATIVE INTERACTION
(A) Amensalism
It is a type of interaction in
which one microorganism
release a specific compound
which has a negative effect
on another microbes.
One Mo’s release a specific
compound which has a
negative effect on other
Mo’s.
Example:- Ant use antibiotic
producing streptomyces to
control fungal parasites in
their fungal garden.

27. Ant use antibiotic producing streptomyces to control the fungal
parasites “Escovopsis”.

28. (B)PARASITISM
it represents a relationship between two living
organisms and is of advantage to one parasite but
is harmful to other(host).the parasite may be
destructive or balanced.

29. MYCOPARASITISM
When one fungus parasites the other, this is known
as mycoparasitism. Often called hperparasitism or
interfungus parasitism.
TWO TYPES:-
• Necrotrophic mycoparasitism:- parasite make
contact with its host, excretes a toxic substances
which kills host cells and utilizes the nutrients
from host.
• Biotrophic mycoparasitism:- parasite obtain
nutrients from living host cells .

30. (C)PREDATION
• It occurs when the microbes, the predator engulf and
digest another microbes(prey).
• The interaction between bdellovibrio bacteria and
other small gram negative bacteria is example of
predation.
• Bdellovibrio is wide spread in aqautic habitats and
attack the other bacteria by boring holes in the wall,
and caused lysis with the eventual release of many
small vibrio shaped bacteria.

31. EXAMPLE OF BDELLOVIBRIO BACTERIUM

32. Cannibalism is the act of
consuming another
individual of the same
species as food.
Cannibalism is a common
ecological interaction in
the animal kingdom and
has been recorded in more
than 1,500 species.
Example :- Snakes,
Humans etc

33. (E)COMPETITION
• This phenomenon was studied by E. F. Gause in
1934.
• It represents negative interaction.
• In which both populations are affected with respect
to their survival & growth.
• In this case, they share the limiting resource like
space, a limiting nutrients while surviving at lower
population level.
Example:- E. Coli & Coliform .
Azotobacter & Cellulomonas

34. COLIFORMS
Competition b/w Coliform bacteria
for food

35. Azotobacter
(nitrogen
Fixer)
Cellulomonas
(cellulose
Degrader)
NH₄
Glucose
Association b/w Azotobacter & Cellulomonas.

36. CONCLUSION
Microorganisms engage in a wide variety of social
interactions, including cooperation.
 The role of microbes in plant growth, nutrient
availability, disease resistance, yield and quality of
medicinal compounds is demonstrated in medicinal
plants.
 There are increasing interests in the research of the
interaction between medicinal plant and their
rhizosphere microbes for the improvement of
medicinal plants.

37. REFERENCES
• Microbiology7th edition by Prescott, Harley and
Klein’s
• Microbiology by R.C. Dubey & D. K. Maheshwari
• Microbiology by R.P. Singh
• General Microbiology by Stanier, Ingraham,Wheelis
& Painter