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MICROBIAL INTERACTIONS, NEGATIVE INTERACTIONS, POSITIVE INTERACTIONS* -…
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NEGATIVE INTERACTIONS
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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.
EXAMPLES
:PROTOZOAN BACTERIA IN SOIL:
Many protozoans can feed on various bacterial population which helps to maintain count of soil bacteria at optimum level
Bdellovibrio, Vamparococcus, Daptobacter etc are examples of predator bacteria that can feed on wide range of bacterial population.
PARASITISM:
- 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.
- The host-parasite relationship is characterized by a relatively a long period of contact which may be physical or metabolic.
EXAMPLES:
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.
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.
COMPETITION:
- The competition represents a negative relationship between two microbial population in which both the population are adversely affected with respect to their survival and growth.
- Competition occurs when both population uses same resources such as same space or same nutrition, so, the microbial population achieve lower maximum density or growth rate.
EXAMPLES:
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.
AMMENSALISM:/(ANTAGONISM):
- When one microbial population produces substances that is inhibitory to other microbial population then this interpopulation relationship is known as Ammensalism or Antagonism.
- It is a negative relationship.
EXAMPLES:
LACTIC ACID PRPDUCED 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.
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THIOBACILLUS THIOOXIDANT:
Thiobacillus thioxidant produces sulfuric acid by oxidation of sulfur which is responsible to lowering of pH in the culture media which inhibits the growth of most other bacteria.
POSITIVE INTERACTIONS*
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SYNTROPHISM:-
It is an association in which the growth of one organism either depends on or improved by the substrate provided by another organism.
In syntrophism both organism in association gets benefits
EXAMPLES:
Methanogenic ecosystem in sludge digester:
Methane produced by methanogenic bacteria depends upon interspecies hydrogen transfer by other fermentative bacteria.
. Lactobacillus arobinosus and Enterococcus faecalis:
In the minimal media, Lactobacillus arobinosus and Enterococcus faecalis are able to grow together but not alone.
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.
MUTUALISM:
- It is defined as the relationship in which each organism in interaction gets benefits from association
.* It is an obligatory relationship in which mutualist and host are metabolically dependent on each other.
- Mutualistic relationship is very specific where one member of association cannot be replaced by another species.
- Mutualism require close physical contact between interacting organisms.
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. EXAMPLES:
LICHENS:
Lichens are excellent example of mutualism.
They are the association of specific fungi and certain genus of algae. In lichen, fungal partner is called mycobiont and algal partner is called
Phycobiont is member of cycanobacteria ad green algae
PROTOZOAN-TERMITE:
Protozoan-termite relationship is the classical example of mutualism in which flagellated protozoan lives in the gut of termites.
PARAMECIUM-CHLORELLA
Paramecium (protozoa) can host Chlorella (algae) within its cytoplasm.
The presence of Chlorella within Paramecium helps to survive protozoa in anaerobic condition as long as there is sufficient light.
.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.
EXAMPLES:
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
FLAVOBACTERIUM (host) and LEGIONELLA PNEUMOPHILA (commensal):
Flavobacterium excrete cystine which is used by Legionella pneumophila and survive in aquatic habitat.
Association of Nitrosomonas (host) and Nitrobacter (commensal) in Nitrification:
Nitrosomonas oxidize Ammonia into Nitrite and finally Nitrobacter uses nitrite to obtain energy and oxidize it into Nitrate.
PROTOCOOPERATION:
- It is a relation in which organism in association is mutually benefits
- This interaction is similar to mutualism but the relationship between the organism in protocooperation.
. Association of Desulfovibrio and Chromatium: it is a protocooperation between carbon cycle and sulfur cycle.
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MARINE WORM-BACTERIAL PROTOCOOPERATION RELATIONSHIP:
- Worm secrete mucous from tiny gland on backs feeds bacteria
QUORUM SENSING(AUTOINDUCTION):
accumulation of signalling molecule enables single cells to sense number of bacteria
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