Microbial intraction

SUBMITTED BY:MONIKA SAPRA
MSc.MICROBIOLOGY
SEM:3rd
ROLL NO.1508

The inter- and intra-relationships between various
microorganisms which can include both positive (like
SYMBIOSIS) and negative (like ANTIBIOSIS)
interactions. Examples include virus - bacteria and
bacteria - bacteria.
The consortium may be in intermitent,cyclic or
permanent.
These are ubiquitous, diverse and critically
important in the function of any biological
community.

These includes-
oNeutralism
oMutualism
oCommensalism
oParasitism
oCooperation
oPredation
oAmensalism
oCompetition
oSynergism

 MICROBE-MICROBE INTERACTION.
 MICROBE-PLANT INTERACTION.
 MICROBE-ANIMAL INTERACTION.
 MICROBE-HUMAN INTERACTIONS.
 MICROBE-ENVIRONMENT INTERACTIONS
AND DISEASES.

Microorganisms have no effect on
each other.
Observed in natural communities if-
 Culture density is low.
 Nutrient level is high.
 Each culture has distinct requirements.

Mutualism
•An obligatory relationship.
•Highly specific.
•They operate as a single organism.
•Both organisms benefit.
•For Eeg.Diatom(Climacodium)
•and cyanobacteria(Epithemia turgida)
•Lichen-Fungi with
Cyanobacteria.

Usnea (fruticose)Xanthoparmelia substrigosa (foliose)
Clim
The endosymbionts are visible as
round bodies within the
cytoplasm. endosymbionts are
important in fixing atmospheric
nitrogen for use by the cells.

Positive but not obligatery symbiosis
Can be separated from one another.
For eg-Desulfovibrio &
Chromatium,Cellulomonas & Azotobactor.

One partner(commensal) benefits.
 while other(host) remains unaffected.
 – Common among organisms, not obligatory
 – Unidirectional
 – Usually, unaffected population modifies the
environment in a way that other population
benefits.
 For eg-during Nitrification ,oxidation of NH4+
ions get convert into nitrate.
 Nitrosomonas convert NH4+ Ions to nitrite and
nitrobacter oxidise nitrite into nitrate.

Parasitism
oOne speices is dependent on a
another for nutrition and growth.
oIn it, one organism is benefitted
and other is harmed.
oClosly related to predation.
oCoexistence between host and
parasite.
oFor eg-Viruses are the highly
specialized intracellular
parasites,generally kill the host.

 cell.Myxococcus xanthus and E.coli.
 Microbial parasite may kill the host or can have
stable relationship without killing the
host.(lysogeny provirus is carried on host
chromosome).
 Pathogenic parasite may attack and kill the plant or
animal host.
 Obligate parasite Treponema
pallidum(syphilis),Rickettsia(Rockey mountain
fever) can’t grow without an appropriate host.

Predatory behavior of M. xanthus
The M. xanthus swarm expands from the
initial spot in a tangled motility pattern.
Lysis ...

 It involves predator species which target other
microbe for material to survive.
 Predator attacks and kills its prey.
 They can be obligate or facultative.
 Members of predatory bacteria are known as
‘Bdellovibrio and like organisms’(BALO).They
can be epibiotic,periplasmic,cytoplasmic.
 For eg-
 Bdellovibrio-E.coli interaction
(Vampirococcus,Daptobacter both attack
Chromatium.

 Focuses on exclusion of an organism from
growing on a specific site to prevent the
utilization of limiting nutrients.
 Unidirectional process based on the release
of a specific compound by one organism that
has negative effect on another.
 Product of one impact another i.e one species
remains uneffected while other is harmed.
 For eg- microbial production of antibiotics that
can inhibits or kill another.penicillin by fungi
inhibit a type of cell wall found

only in bacteria.
Bacteriocins-kill the strains of closely
related species by generating holes in
plasma membrane
Metabolic end products.

 It arises when different organisms within
population try to acquire same resources.
 Both the species are harmed.
 Competiton within the species or among
different species can be attributed to
availibility of Nitrogen source,carbon
source,electron donors,electron
accepter,vitamins,light,water.
 Competition may result in exclusion of other
species or the establishment of a steady state
where multiple species coexist.

Eg- In aquatic environment where
extensive phototrophic activity results in
blooms of single species of diatoms or
cyanobacteria.
Thermophilic springs chemolithotrophic
organisms are selected.
Lactic acid fermentation of food.
Large intestine of animals,a single species
doesn’t dominate but a mixed population
coexist.

 Two species are required for growth on a specific
electron donor that is not metabolized by either
organism alone or one of the organisms remove end
products of metabolism from other,which enables both
the organisms to grow.
 Both the species are benefited.
 This relationship was discovered by Meyer Wolin and
colleagues,when fermentation of propionic acid
occurred when there was a coculture.
 Synophobacter produces H during fermentation and
accumulation of H makes the reaction
thermodynamically unstable.
 Pesence of methanogen,Methanospirillum makes the
oxidation favourable by consuming the H.’

 Different interactions between
microorganisms and plants have been
identified and the most obvious environment
for such interactions is soil.
 Microbe-plant association can be mutulistic(a
highly specialized interaction where there is
considerable specificity found in mutulistic
activities)or it can be
commensilistic(secretions from plants benefit
bacteria and fungi but no apparent benefit to
plant.

 Beneficial aspects of plant-microbe symbiosis
are,plants provide c-material to support growth of
microbes and microbes promote plant growth by
supplying minerals or N2.
 Eg.Azolla(fresh water aquatic fern)lives in
symbiotic association with Anabena azollae ,where
cyanobacteria fixes atmospheric N2and Azolla
provides carbohydrates.cyanobacteria are present
in trichomes and nutrient exchange occurs through
tiny fibres extending from plant to cavity.

 Mucilage,organic acids(rhizodepozition),dead root cells(nucleic
acid,complex carb.,proteins)released by root tip act as c-source for
microbes.
 Microorganisms enhance the cycling of c and N
compounds,consume rhizospheric O and lower the redox potential of
rhizosphere.
 Eg.Mycorrhizae-mutulistic relationship between fungus and
plantroot,growth on exterior of the root is the characteristic of
ectomycorrhiza while growth inside the root is attributed to
endomycorrhiza.
 Plants with mycorrhiza-
 can grow in low nutrient soil.
 display greater growth rates.
 more disease resistent.
 Boletus elegans and larix sp.
 Gigaspora margarita and cotton.
Fungus-Root system

 Enzyme system for N2 fixation is present only in
prokaryotes and nodules are associated with roots
of Leguminous plants,bacteria(rhizobia) are
specific for a legume species.
 Assciation is beneficial for both,plant provide c and
energy source to bacteria and bacteria fix N2 and
provide amino acid to plant.
 Rhizobium leguminosarum sp.and pea, beans
tropical(root nodules).
 Azorhizobium caulinodan and Aquatic tropical
legume(stem nodule).

 Bacteria and fungi interact with humans and other animals and this
interaction can be symbiotic, commensalistic or parasitic.
 Symbiotic relationships are widespread and has evolved new
metabolic capabilities and cellular structures.(symbiogenesis).
 Evolutionary benefits in a symbiotic relationship are;-provision of
dietary needs that their hosts lack including essential amino
acids,cofactors,metabolic factors etc.
 N storage and recycling.
 Large alterations in genome of symbionts and adaptations by host to
favour the symbiosis occur during long association which can be in
form of genome size reduction or increase in AT content in
genome.since endosymbionts protect their hosts from pathogens,this
may have influenced the evolution of sociality in animals to acquire
the endosymbiont through horizontal and vertical transmission.

 Buchnera aphidicola and Wiglesworthia glossinidia are
examples of primary symbionts showing marked genome
reduction and resultant genome is the commitment to a
symbiotic lifestyle.
 Secondary symbionts may have negative or positive
effect on host and are generally facultative and their
genomes indicate that they are adapting themselves to
an obligate mutulism.

Glossina sp., which houses Wigglesworthia
glossinidia

 In vertebrates gut microbial community produce vitamins
needed by host,help digetion and colonization resistence.
 Termite(Reticulitermis speratus) gut
community(symbioses within symbiosis) responsible for
cellulose degradation include
bacteria(spirochaetes,TG1,2,3,bacteroidetes,firmicutes)
which provideN-comp. by fixing N2 and nutrients to host
and protists with their bacterial and archeal ecto and
endosymbionts degrade cellulose,provide a.acid and
cofactors to protists.
 Ambrosia beetle carries fungus to a new environment
where fungus flourishes beetle uses fungus as food.

 One fascinating parasitic interaction involves
nematod(Heterorhabditis bacteriophora harboring a bacterial
endosymbiont Photorhabdus luminescens) and parasitize insects
and humans.
The beneficial nematodes can be used to control a broad range of
soil inhabiting insects and above ground insects in their soil
inhabiting stage of life. White grubs, Beetle grubs, Japanese beetle
 This nematod arrest their development in a phase called infective
juvinile larval stage at which it is infected by endosymbiont and when
it infects the insect,nematod further development is induced by
insects hemolymph.
 Endosymbiont secretes proteases supressing insects immune
system and damage the insect and nematod parasite feeds on
endosymbiont and the insect as well.

Photorhabdus fluorescent bacteria within a
Heterorhabditis nematode

 Comensal(species that benefits from association)
may obtain nutrient,shelter, support,locomotion
from the host species which remains unmodified.
 Comensal species may show great structural
adaptation.eg.Titan triggerfish(Balistoides
viridescens) which creates feeding opportunities
for smaller fishes by moving large rocks too big for
them to shift themselves.
 Another example is of a vulture which eats the
leftover food from a lion and the lion is not affected
by this while the vulture gets to eat.

Titan trigger fish
Vultures eating the leftover food

Microbial intraction

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