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Synergism

	Synergism As already discussed above, proto-cooperation is a non-obligatory relationship between two organisms which satisfy each other's needs. It results in various kinds of actions: Syntrophism is a kind of synergism where the organisms satisfy their nutritional needs. This is exhibited in a number of ways: 1. Arginine is converted to putresciene by E.coli and Enterococcus faecalis both working together. E.faecalis can convert arginine into ornithine and E.coli further converts ornithine to putresciene, a task which cannot be performed by either of the organisms alone.
Thus by remaining together both the organisms' nutritional needs are being fulfilled. In other words, both the organisms allow the completion of a metabolic pathway that otherwise would not be completed. 2. Many allow supply of growth factors by one population for another. For example, Nocardia and Pseudomonas together can degrade cyclohexane wherein Nocardia acts on cyclohexane and supplies metabolic products to Pseudomonas and in turn the bacterium supplies biotin to Nocardia. 3. Similar relationship is seen between Lactobacillus arabinosus and Streptococcus faecalis based on the mutual exchange of required growth factors.
L.arabinosus requires phenylalanine for growth, which is produced by S.faecalis which in turn requires folic acid produced by L.arabinosus. In a minimal medium both populations can grow together, but neither population can grow alone. 4. In another relationship between Chlorobium (green alga) and Desulfovibrio (chemolithotrophic bacterium), Chlorobium fixes carbon dioxide through photosynthesis.
It uses H2S as the electron donor which it oxidises in the process to sulphur. This elemental sulphur is used by Desulfovibrio which reduces it to H2S. It also makes use of the organic carbon supplied by the alga (for its growth) and supplies CO2 which is taken up by the alga for photosynthesis 5. Similar relationship can be seen among the bacterial population involved in nitrogen cycle. Heterotrophic pseudomonads are chemotactically attracted to organic excretions formed by heterocysts of Anabaena spiroides.
	They form dense aggregates around the heterocysts. Few bacteria are associated with photosynthetic cells of the filamentous alga. Pseudomonas oxidise the organic products released by the alga and thus stimulate nitrogenase activity (by lowering the oxygen concentration). 6. Some bacteria remain epiphytic on algal members taking up the preformed organic matter and oxygen (supplied by algae) and in turn supply carbon dioxide and vitamins for the algal members to flourish. Some synergistic relationships are based on the ability of second population to accelerate the growth rate of the first one. For example, the action of Brevibacterium and Curtobacterium which take up the excreted organic carbon given out due to metabolism of orcinol by Pseudomonas, helps in the acceleration of growth of Pseudomonas which would have otherwise declined in in its growth due to accumulation of the metabolic products.

7. Synergistic relationships also allow microorganisms to produce enzymes that are not produced by either populations alone. For example, Pseudomonas strains (closely related species) produce lecithinase when grown together but not alone (as a single strain).

8. Degradation pathways of agricultural pesticides involve synergistic relationships. For example, Arthrobater and Streptomyces together degrade organophosphate insecticide Diazinon, a task which they cannot perform alone.

9. Another example is provided by Penicillium piscarium and Geotrichum candidum which remove toxic factors and produce useful substrates from insecticides. Both together detoxify the pesticide propanil. Penicillium cleaves propanil into propionic acid and 3,4-dichloroaniline (toxic) which is further detoxified by Geotrichum.

10. Archaeal population involved in methane production (methanogens) have interesting synergistic relationships with bacterial and other microbial population. The names of these bacterial genera indicate their syntrophic relationships with hydrogen consuming methanogenic archaea. Syntrophomonas species oxidise butyric acid and caproic acid to acetate and H2. Syntrophobacter oxidises propionic acid to acetate, CO2 and H2. The acetate and H2 produced by these bacteria are used by methanogenic archaea to produce methane. Thus the metabolism of the methanogens maintains very low concentrations of H2 thus increasing the growth rates of Syntrophomonas and Syntrophobacter species

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