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7/24/2019 ecology PART 2 2015-2016.pptx
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MICROBIAL
INTERACTIONS
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Mutualism
Some reciprocal benefit to both
partners
Relationship with some degree of
obligation
often partners cannot live separately mutualistand host are dependent on
each other
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Examples
Lichensthe association between specific fungui and
certain genera of either green algae orcyanobacteria.
mycobiont fungal partner
provides water, minerals, protectedenvironment and firm substratum for
growth phycobiont
alga or cyanobacterium
provides organic carbon and oxygen
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Figure 30.14
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Mycorrhizae
represent a mutualisticsymbiosis between the root
system of higher plants andfungal hyphae.
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Advantages
. !he fungus derives nutrients via the root of the
plant. Sugars formed in the leaves move down the
stem as sucrose
". !he fungal hyphae act li#e a massive root hair
system, scavenging minerals from the soil andsupplying them to the plant.
$. %ecause of this associationship the plant partner, in
addition to the nutritional benefits, develops
drought resistance, tolerance to p& andtemperature extremes, and greater resistance to
pathogens due to 'phytoalexins( released by the
fungus.8
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)ctotrophic Mycorrhiza
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)ndotrophic Mycorrhiza
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Syntrophism growth of one organism depends on or is improved
by growth factors, nutrients, or substrates providedby another organism growing nearby also called crossfeeding
is also defined as a mutualistic interrelationship
between two different microorganisms whichtogether degrade some substances *and conserveenergy doing it+ that neither could degradeseparately. n most cases of syntrophism the nature of a
syntrophic reaction involves &"gas beingproduced by one partner and being consumed bythe other.
!hus, Syntrophy has also been called interspecies
hydrogen transfer.
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Example
Anaerobic methanogenic ecosystems
fatty acids catabolized by anaerobic bacteria
*e.g.,Syntrophobacter+, producing &"
methanogen *e.g.,Methanospirillum+ uses &"
for methanogenesis
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protocooperation
%enefits both organisms inrelationship
-iffers from mutualism becauseprotocooperative relationship is notobligatory
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)xamples of protocooperation
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Nocardiapopulation metabolizescyclohexane resulting in degradation
products that are used by
Pseudomonaspopulation. !hepseudomonasspecies produce biotin
and growth factors that are reuiredfor the growth of /ocardia.
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0ommensalism
1ne organism benefits and the
other is neither harmed nor
helped 0ommensal is the organism that
benefits
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Examples of Commensalism
. the waste product of one microorganism is the
substrate for another species. An example is
nitrification
/&$/1" /1$/itrification carried out by two different
bacteria
e.g.,Nitrosomonas carries out first step
e.g.,Nitrobactercarries out second step *i.e., it
benefits from its association withNitrosomonas+
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". 0an also involve modification of
environment by one organism, ma#ing
it more suited for another organism
. 2or example, when facultative anaerobes
utilize oxygen and lower the oxygen
content, they create anaerobic habitatwhich favor the growth of obligate
anaerobes because the latter benefit from
the metabolic activities of the facultativeanaerobes in such a habitat. , such as the
oral cavity and human intestine, is
dependent on such commensal relationship.18
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$. 0ommensalism also is important in the
colonization of the human body.
. 2or example, A disease causingmicrobial population when a lesion on
the surface, it creates an entry3passage
for other microbial population thatotherwise could not enter and grow in
the host tissues. 2or convenience,
Mycobacterium leprae, the causative agent
of leprosy, open lesions on the body3
surface and thus allow other pathogens to
establish secondary infections.
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