This document discusses various types of microbial interactions, including positive interactions like mutualism, syntrophism, and commensalism as well as negative interactions such as competition, parasitism, and predation. Specific examples are provided to illustrate each type of interaction, such as lichens exhibiting mutualism and lactic acid bacteria demonstrating commensalism in the human vaginal tract. Both beneficial and harmful relationships between microorganisms are explored.
2. Microbial interaction
• Microorganisms interacts with each other and can be physically
associated with another organisms in a variety of ways.
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Organisms
located on surface
of another
ECTOBIONT
Located within
another
organisms
ENDOBIONT
3. Types of Microbial interaction
POSITIVE
Mutualism
Proto-
cooperation
Commensalism
NEGATIVE
Ammensalism
Parasitism
Predation
Competition
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4. Types of Microbial interaction
POSITIVE INTERACTION
Both the organisms gets
benefits
Obligatory relationship –
host metabolically
dependent on each other
Require close contact
between the organisms
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5. Examples of mutualism
1
• Lichens are excellent example of
mutualism.
• association of specific fungi and certain
genus of algae
2
• fungal partner is called mycobiont
• algal partner is called Phycobiont
3
• phycobionts are photoautotrophs, the
fungus get its organic carbon directly from
algal partner, in turn fungi protects the
phycobiont from extreme conditions and
also provide water and minerals to algae
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6. 1
• Paramecium (protozoa) can
host Chlorella (algae) within its
cytoplasm.
2
• The algae Chlorella provide the
protozoan partner with organism
carbon and O2, in turn protozoa
provide protection, mortility, CO2
and other growth factors
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7. 2. Syntrophism
•It is an association in which the growth of one organism either depends on or improved
by the substrate provided by another organism.
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EXAMPLE - Lactobacillus arobinosus and Enterococcus faecalis
1
• In the minimal media, Lactobacillus arobinosus and Enterococcus faecalis are
able to grow together but not alone.
2
• The synergistic relationship between E. faecalis and L. arobinosus occurs in which
E. faecalis require folic acid which is produced by L. arobinosus and in turn
lactobacillus require phenylalanine which is produced by Enterococcus faecalis.
8. 3.Protocooperation
•It is a relationship in which organism in association is mutually benefited
with each other.
•This interaction is similar to mutualism but the relationships between the
organisms in protocooperation is not obligatory as in mutualism.
Examples of Protocooperation:
•i. Association of Desulfovibrio and Chromatium: it is a protocooperation between carbon
cycle and sulfur cycle.
•ii. Interaction between N2-fixing bacteria and cellulolytic bacteria such as Cellulomonas
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9. 4. Commensalism:
•It is a relationship in which one organism (commensal) in the association is benefited
while other organism (host) of the association is neither benefited nor harmed
•It is an unidirectional association and if the commensal is separated from the host, it can
survive.
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10. Example
Non-pathogenic coli in intestinal tract of human: E.
coli is a facultative anaerobe that uses oxygen and
lower the O2 concentration in gut which creates
suitable environment for obligate anaerobes such
as Bacteroides. E. coli is a host which remains
unaffected by Bacteroides.
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11. Types of Microbial interaction
NEGATIVE INTERACTION
Amensalism
•When one microbial population produces substances that is inhibitory to other microbial
population then this inter population relationship is known as Ammensalism or Antagonism.
•It is a negative relationship.
•The first population which produces inhibitory substances are unaffected or may gain a
competition and survive in the habitat while other population get inhibited. This chemical
inhibition is known as antibiosis.
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12. Examples of antagonism (amensalism):
•i. Lactic acid produced by lactic acid bacteria in vaginal tract:
•Lactic acid produced by many normal floras in vaginal tract is inhibitory to many
pathogenic organisms such as Candida albicans.
•ii. Skin normal flora:
•Fatty acid produced by skin flora inhibits many pathogenic bacteria in skin
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13. Competition represents a negative relationship
Competition occurs when both population uses
same resources such as same space or same
nutrition
Competition inhibits both population from occupying
exactly same ecological niche because one will win the
competition and the other one is eliminated
Competition
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14. Examples of competition:
• i. Competition between Paramecium
cadatum and Paramecium aurelia:
• Both species of Paramecium feeds
on same bacteria population when
these protozoa are placed together.
• P. aurelia grow at better rate
than P. caudatum due to
competition.
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15. •Some parasite lives outside host cell, known as
ectoparasite while other parasite lives inside host cell,
known as endoparasite
The host-parasite relationship is characterized by a relatively
a long period of contact which may be physical or metabolic
It is a relationship in which one population (parasite) get
benefited and derive its nutrition from other population (host)
in the association which is harmed
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16. Examples of parasitism:
•i. Viruses:
•Viruses are obligate intracellular parasite that
exhibit great host specificity.
•There are may viruses that are parasite to
bacteria (bacteriophage), fungi, algae,
protozoa etc.
•ii. Bdellovibrio:
•Bdellavibrio is ectoparasite to many gram
negative bacteria.
•The parasite Bdellovibrio penetrate the outer
membrane of its host and enters periplasmic
space but not inside host cytoplasm.
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17. Predation:
•It is a wide spread phenomenon when one organism (predator) engulf or
attack other organism (prey).
•The prey can be larger or smaller than predator and this normally results
in death of prey.
•Normally predator-prey interaction is of short duration.
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18. Examples of Predation:
• i. Protozoan-bacteria in soil:
• Many protozoans can feed
on various bacterial
population which helps to
maintain count of soil
bacteria at optimum level
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