This document summarizes a seminar on microbial interactions and microbial ecology. It discusses various types of microbial interactions including mutualism, cooperation, commensalism, parasitism, predation, amensalism, and competition. Specific examples of each type of interaction are provided, such as termite-protozoan mutualism, sulfide-based mutualism at hydrothermal vents, and antibiotic production as an example of amensalism. The document also discusses human-microbe interactions and the normal microbiota found in different parts of the human body.

1. SEMINAR ON
MICROORGANISMS INTERACTION AND MICROBIAL ECOLOGY
PRESENTED BY:
TAHURA MARIYAM
M.Sc. MICROBIOLOGY (Sem -II)
P.ID: 19MSCMB009
DEPARTMENT OF INDUSTRIAL MICROBIOLOGY
JACOB INSTITUTE OF BIOTECHNOLOGY AND BIO-ENGINEERING
SAM HIGGINBOTTOM UNIVERSITY OF AGRICULTURE,TECHNOLOGY, AND SCIENCES,
PRAYAGRAJ

2. CONTENT
• Introduction
• Microbial interaction
• Mutualism
• Microorganism- insect mutualism
• Zooxanthellae
• Sulfide-based mutualism
• Methane- based mutualism
• Cooperation
• Commensalism
• Predation
• Parasitism
• Amensalism
• Competition
• Human- microbe interaction
• Gnotobiotic animals
• Normal microbiota of the human body
• The relationship between normal microbiota and the host

3. INTRODUCTION
• The term symbiosis, or “together-life,” can be used to describe many of the interactions
between microorganisms, and also microbial interactions with higher organisms,
including plants and animals. These interactions may be positive or negative.
• Symbiotic interactions include
mutualism,cooperation,commensalism,parasitism,predation,amensalism,and competition.
These interactions are important in natural processes and in the occurrence of disease.
The interactions can vary depending on the environment and changes in the interacting
organisms.

4. MICROBIAL
INTERACTION
Microorganisms can associate physically with
other organisms in a variety of ways. One
organism can be located on the surface of
another, as an ectosymbiont. In this case, the
ectosymbiont usually is a smaller organism
located on the surface of a larger organism. In
contrast, one organism can be located within
another organism as an endosymbiont. While
the simplest microbial interactions involve two
members, a symbiont and its host, a number of
interesting organisms host more than one
symbiont.

6. MUTUALISM
• Mutualism defines the relationship in which some
reciprocal benefit accrues to both partners. This is
an obligatory relationship in which the mutualist
and the host are dependent on each other.
1. Microorganism-Insect Mutualism
2. Zooxanthellae
3. Sulfide-Based Mutualism
4. Methane-based mutualism
1) Microorganism-Insect Mutualisms:
Mutualistic associations are common in the insects.
This is related to the foods used by insects, which
often include plant sap or animal fluids lacking in
essential vitamins and amino acids.
Mutualism. Light micrographs of (a) a worker termite of
the genus Reticulitermes eating wood and (b)
Trichonympha, a multiflagellated protozoan from the
termite’s gut. The ability of Trichonympha to break down
cellulose allows termites to use wood as a food source.
(a) (b)

7. Wolbachia pipientis, this
rickettsia infects more
organisms than does any
other microbe. Wolbachia
inhabits the cytoplasm of
these animals where it
apparently does no harm.
(a) Wolbachia pipientis Within the
Egg Cytoplasm of the Ant
Gnamptogenys menadensis. In this
insect, Wolbachia is maternally
transmitted, so the bacterium has
evolved mechanisms to manipulate
the sex distribution of the offspring so
that the host produces mostly
females. The Wolbachia cell is
indicated by (B) and host
mitochondria are labeled m.
(b) River blindness. This is the
second-leading cause of
blindness worldwide. Evidence
suggests that it is not the
nematode but its endosymbiont,
Wolbachia pipientis, that causes
the severe inflammatory
response that leaves many, like
the man shown here, blind.
(b)(a)

8. Zooxanthellae. (a) Zooxanthellae (green) within the tip of a hydra tentacle. (b) The green
color of this rose coral (Manilina) is due to the abundant zooxanthellae within its tissues.
2) ZOOXANTHELLAE
(a) (b)

9. Hydrothermal Vents and Related Geological Activity: The chemical reactions between seawater and rocks that
occur over a range of temperatures on the seafloor supplies the carbon and energy that support a diverse collection
of microbial communities in specific niches within the vent system
3) Sulfide-
Based
Mutualism

10. The Tube Worm–Bacterial Relationship. (a) A community of tube worms (Riftia pachyptila) at the Galápagos Rift hydrothermal vent site
(depth 2,550 m). Each worm is more than a meter in length and has a 20 cm gill plume. (b, c) Schematic illustration of the anatomical and
physiological organization of the tube worm. The animal is anchored inside its protective tube by the vestimentum. At its anterior end is a
respiratory gill plume. Inside the trunk of the worm is a trophosome consisting primarily of endosymbiotic bacteria, associated cells, and
blood vessels. At the posterior end of the animal is the opisthosome, which anchors the worm in its tube. (d) Oxygen, carbon dioxide, and
hydrogen sulfide are absorbed through the gill plume and transported to the blood cells of the trophosome. Hydrogen sulfide is bound to the
worm’s hemoglobin (HSHbO2) and carried to the endosymbiont bacteria. The bacteria oxidize the hydrogen sulfide
and use some of the released energy to fix CO2 in the Calvin cycle. Some fraction of the reduced carbon compounds synthesized by the
endosymbiont is translocated to the animal’s tissues.

11. 4) METHANE-BASED MUTUALISMS
• Other unique food chains involve methane-fixing microorganisms. By
converting methane to carbohydrate, these bacteria perform the first
step in providing organic matter for consumers.
CH4 + 2O2 → CO2 + H2O
• The resulting CO2 is then readily fixed by the plant, which uses the
Calvin cycle:
2CO2 + 2H2O → 2CH2O + 2O2
• This enables extremely efficient carbon recycling within this ecosystem:
CH4 + 2CO2 → 2CH2O
• The Rumen Ecosystem: Ruminants are the most successful and
diverse group of mammals on Earth today. Examples include cattle,
water buffalo, goats, giraffes, and caribou. It is thought that the
ruminants evolved an “eat now, digest later” strategy because their
grazing can often be interrupted by predator attacks.
Ruminant Stomach. The stomach
compartments of a cow. The
microorganisms are active mainly in the
rumen. Arrows indicate direction of food
movement.

12. COOPERATION
• Cooperation and commensalism are two
positive but not obligatory types of
symbioses found widely in the microbial
world. These involve syntrophic
relationships. Cooperation benefits both
organisms. A cooperative relationship is
not obligatory and, for most microbial
ecologists. Examples of Cooperative Symbiotic Processes.
(a) The organic matter (OM) and sulfate required by Desulfovibrio are
produced by the Chromatium in its photosynthesis-driven reduction of
CO2 to organic matter and oxidation of sulfide to sulfate. (b)
Azotobacter uses glucose provided by a cellulosedegrading
microorganism such as Cellulomonas, which uses the nitrogen fixed by
Azotobacter.

13. A Marine Crustacean-Bacterial Cooperative
Relationship. (a) A picture of the marine shrimp Rimicaris
exoculata clustered around a hydrothermal vent area,
showing the massive development of these crustaceans in
the area where chemolithotrophic bacteria grow using
sulfide as an electron and energy source.The bacteria,
which grow on the vent openings and also on the surface of
the crustaceans, fix carbon, and serve as the nutrient for
the shrimp. (b) An electron micrograph of a thin section
across the leg of the marine crustacean Rimicaris
exoculata, showing the chemolithotrophic bacteria that
cover the surface of the shrimp. The filamentous nature of
these bacteria, upon which this commensalistic relationship
is based, is evident in this thin section.(a)
(a)
(b)
(b)
A Marine Nematode-Bacterial Cooperative
Relationship. Marine free-living nematodes,
which grow at the oxidized-reduced interface
where sulfide and oxygen are present, are
covered by sulfide-oxidizing bacteria. The
bacteria protect the nematode by decreasing
sulfide concentrations near the worm, and the
worm uses the bacteria as a food source. (a) The
marine nematode Eubostrichus parasitiferus with
bacteria arranged in a characteristic helix pattern.
(b) The chemolithotrophic bacteria attached to the
cuticle of the marine nematode Eubostrichus
parasitiferus. Cells are fixed to the nematode
surface at both ends.

14. COMMENSALISM
• Commensalism is a relationship in which one symbiont, the commensal, benefits
while the other (sometimes called the host) is neither harmed nor helped. Various
fermentative bacteria produce low molecular weight fatty acids that can be
degraded by anaerobic bacteria such as Syntrophobacter to produce H2 as
follows:
Propionic acid → acetate + CO2 + H2
• Syntrophobacter uses protons (H+
+ H+
→ H2) as terminal electron acceptors in
ATP synthesis. The bacterium gains sufficient energy for growth only when the H2
it generates is consumed. The products H2 and CO2 are used by methanogenic
archaea such as Methanospirillum as follows:
4H2 + CO2 → CH4 + 2H2O

15. PREDATION
• Predation among microbes involves a
predator species that attacks and usually
kills its prey.
• Bdellovibrio is an active hunter that is
vigorously motile, swimming about looking
for susceptible gram-negative bacterial prey.
• Vampirococcus attaches itself as an epibiont
to the outer membrane of its prey. It then
secretes degradative enzymes that result in
the release of the prey’s cytoplasmic
contents.
• In contrast, Daptobacter penetrates the prey
cell and consumes the cytoplasmic contents
directly.
Examples of Predatory Bacteria Found in
Nature. (a) Bdellovibrio, a periplasmic predator that penetrates the cell wall
and grows outside the plasma membrane, (b) Vampirococcus with its
unique epibiotic mode of attacking a prey bacterium, and (c) Daptobacter
showing its cytoplasmic location as it attacks a susceptible bacterium.

16. PARASITISM
• Parasitism is one of the most complex microbial interactions; the
line between parasitism and predation is difficult to define. This
is a relationship between two organisms in which one benefits
from the other, and the host is usually harmed. One good
example is the disease typhus. This disease is caused by the
rickettsia Rickettsia typhi, which is harbored in fleas that live on
rats. It is transmitted to humans who are bitten by such fleas, so
in order to contract typhus, one must be in close proximity to rats.

17. AMENSALISM
• Amensalism describes the
adverse effect that one
organism has on another
organism. This is a
unidirectional process based
on the release of a specific
compound by one organism
which has a negative effect on
another organism. A classic
example of amensalism is the
production of antibiotics that
can inhibit or kill a susceptible
microorganism.
Amensalism: An Adverse Microbe-Microbe Interaction. (a) Antibiotic production and inhibition of growth of
a susceptible bacterium on an agar medium. (b) A schematic diagram describing the use of antibiotic-
producing streptomycetes by ants to control fungal parasites in their fungal garden. (c) Coevolution of attine
ants and the antibiotic-producing Pseudonocardia has resulted in specialized localization of the bacterium on
the ant.This rooted tree illustrates the phylogeny of fungus-growing ants; column A shows the placement of the
bacteria on the ants’ body, column B presents scanning electron micrographs of the areas colonized by the
microbe.

18. COMPETITION
• Competition arises when different organisms within a population
or community try to acquire the same resource, whether this is a
physical location or a particular limiting nutrient.

19. HUMAN-MICROBE INTERACTION
• The microorganisms normally associated with the human body, are normal microbial flora or
microbiota.
• Interactions between host and microbe are dynamic, permitting niche fulfillment that
maximizes benefit to the microbe and, in some cases, the host. Microbial niche variations are
also related to age, gender, diet, nutrition, and developmental stage of the host.
• A pathogen is any disease-producing microorganism. Here we introduce the normal human
microbiota, which function not as pathogens but as symbionts that are part of the host’s first
line of defense against harmful infectious agents.

20. • GNOTOBIOTIC
ANIMALS:
• The term gnotobiotic has been defined in two ways.
Some think of a gnotobiotic environment or animal as
one in which all the microbiota are known. Gnotobiotic
refers to a microbiologically monitored environment or
animal that is germfree or in which the identities of all
microbiota are known.
• Louis Pasteur first suggested that animals could not
live in the absence of microorganisms. Attempts
between 1899 and 1908 to grow germfree chickens
had limited success because the birds died within a
month. Thus it was believed that intestinal bacteria
were essential for the adequate nutrition and health of
the chickens. Gnotobiotic refers to a microbiologically
monitored environment.
Raising Gnotobiotic Animals. (a) Schematic of a gnotobiotic isolator.The
microbiological culture media monitor the sterile environment. If growth
occurs on any of the cultures, gnotobiotic conditions do not exist. (b)
Gnotobiotic isolators for rearing colonies of small mammals.
(a)
(b)

21. NORMAL MICROBIOTA OF THE HUMAN BODY
• In a healthy human the internal tissues (e.g., brain, blood, cerebrospinal fluid,
muscles) are normally free of microorganisms. Conversely, the surface tissues
(e.g., skin and mucous membranes) are constantly in contact with
environmental microorganisms and become readily colonized by various
microbial species.

22. Normal Microbiota of a Human: A compilation of microorganisms that constitute normal
microbiota encountered in various body sites.

23. THE RELATIONSHIP BETWEEN NORMAL MICROBIOTA
AND THE HOST
• The interaction between a host and a microorganism is a dynamic process in
which each partner acts to maximize its survival. In some instances, after a
microorganism enters or contacts a host, a positive mutually beneficial
relationship occurs that becomes integral to the health of the host.

24. REFERENCE
Prescott, Harley, and Klein’s Microbiology. Lisa A.
Bruflodt, editor. Prokaryotic Cell Structure and
Function, 7th ed. Colin Wheatley/Janice Roerig-
Blong; 2008. p. 717-739.