Interrelationship between microorganisms – Beneficial and harmful relationship

  • Microorganisms live in the soil, not in the form of pure culture, but as complex populations.
  • Each particle of soil contains more than one type of organisms. So, microbial ecosystem of soil is the sum of the biotic and the abiotic components of soil.
  • Many of these organisms depend upon one another for direct and indirect nutrients. Some complete with one another for energy sources and for the elements and components used as nutrients.
  • This results in the formation of numerous associations among the soil micro organic.
  • The composition of the microflora of any habitat is governed by the biological equilibrium created by the associations and interactions of all individual found in the community.
  • The micro organic that inhabits the soil exhibited many different types of associations or interactions.
  • Some of the associations are indifferent or neutral, some are beneficial type of interactions and others are detrimental or negative.

Beneficial / positive interactions

a. neutralism
b. Symbiosis / mutualism
c. Protoco-operation
d. Communalism
A). Neutralism
  • It is a type of neutral association, in two microorganisms behaves entirely independently or eg: Each could utilize different nutrients with out producing metabolic end products that are inhibitory.
  • This might be transitory as the condition change in the environment, particularly the availability of nutrients, the relationship might change.

Symbiosis / Mutualism

  • Mutualism is a form of symbiosis in which both organisms benefit.
  • An example of mutualism is a clownfish and sea anemones. The clownfish gets protection, while the sea anemones become clean.
  • This is mutualism, because both water animals benefit from having each other around
B). Proto co-operation
  • One type of mutualistic association is that involving the exchange of nutrients between two species, a phenomenon called syntrophism.
  • Many micro organic synthesize the vitamins and anaerobic acids in excess of their nutritional requirements.
  • Others have a requirement of one or more of these nutrients.
  • Hence certain combinations of species will grow together but not apart when nutrient levels are very low.
  • Nutritional proto co-operation has been demonstrated in cultures. Eg: In a medium deficient in nicotinic acid and biotin, neither Proteus vulgaris nor Bacillus polymyxawill multiply as the former (B) requires nicotinic acid and the latter biotin.
  • In mixed culture, in the same medium however both grown since the partner bacterium synthesizes the missing vitamins.
C) Symbiosis
  • The living together of two or more organisms; microbial association Symbiotic association is evident in soil among several groups of organisms algae and fungi in lichens, bacteria residing with in protozoa cells, bacteria and roots in the legume symbiosis, fungi and roots in mycoorhizae.
  • In lichens, the algae and fungi are in such an intimate physical and physiological relationship that the lichens they make are classified as distinct organism.
  • The alga benefits in part are se of the protection afforded to it by the hyphae that envelop and protect it from environmental stresses.
  • While, the fungi gains by making use of the CO2fixed by its photosynthetic partner.
  • Where BGA participants, the heterotraph benefits from the fixed N2.Symbiotic relationship exists between micro and macro organisms.
  • R-L associate N2 fixed is transferred to legume and organic which is transferred to the by CO2metabolizing legume host.

D) Commensalisms
  • It is the type of beneficial association, in which only one species derives benefit while the other is unaffected.
  • This occurs commonly in soil with respect to degradation of complex molecules like cellulose and lignin.
  • One patter can attack a substrate not available to the second organism, but the decomposition results in the formation of products utilized by the second.
  • The one which offer eg:
(1) Many fungi able to degrade cellulose and yield glucose and organic acids. This can serve as a which source for many bacteria and fungi, which are non cellulolytic
(2) The second type of commensal association arises from the need of many micro organic for growth factors. These compounds are synthesized by many micro organisms and their exertion permits the proliferation of nutritionally fastidious soil inhabitants.

Negative / harmful / deleterious interactions

• Detrimental effects of one species on its neighbours are quite common in soil, and they are ditched by the decreases in abundance or metabolic activities of the susceptible organisms.

This include,

  1. Competition
  2. Amensalism
  3. Parasitism and
  4. Predation
  5. Parasitism


A. Competition
    • It is the rivalry for limiting nutrients or other common needs. In such situations the best adapted microbial species will predominate or infect, eliminate other species which are dependent upon the same limited nutrient substances.
    • Eg: Competition between strains derived from soil and those applied with legume seeds at the time of sowing.
    • The better competitor involves the root hairs more frequently and it is responsible for a high % of nodules.
B. Amensalism
  • It is a negative interaction, in which the release of products by one species is toxic to its neighbors.
  • Antagonism is a type of ammensalism.


C. Antagonism

  •  The killing, injury or inhibition of growth of one species of micro organisms by another or when one organism adversely affects the environmental of the other is refered as antagonism.
  •  he toxic compounds are antibiotic. An antibiotic is a substance formed by one organic that in low concentrations inhibits the growth of another organism.
  • Antibiotics are common among Streptomyces isolates, but numerous strains of Micromonespora and Nocardiaare also active.
  • The most common frequently encountered (B) synthesis antibiosis are species of Bacillusstrains of Pseudomonasspecies of Peniciliu, Trichoderma, Aspgerillus, Fusarium are also excrete antibiotic substance.


D. Predation

  • Direct attack of one organism on another predation is one of the most dramatic interrelationships among the micro organic in
  • nature of the many microscopic inhabitants of soil, the bacteria stand out as particularly prove to the attach of predators.
  • The most numerous predators on (B) are protozoans, which by feeding on the billions of (B) undisputedly affect their populations.
  • Protozoans are a key factor in limiting the size of bacterial populations. Probably reducing the abundance of cells and serving to maintain a diverse community.
  • Myxobacteria and cellular slime molds also affect by feeding directly on them
  • Bacteria of the diverse genera are attacked by bacteriophages
  • Bdellovibriois ubiquitous, capable of attacking a number of bacterial genera.
  • Parasitism is between two types of (B), or between different organisms of the same group (F, B, A).
  • Creation of conditions by one organism which are unfavorable for the growth of another (change in pH).
  • Production of specific substances by one organisms which are injurious to growth of other ( organic alcohols, quinones and antibiotics)
  • Direct parasitism of one organism upon another-various effects of (F) upon (B), of (B) upon (F).


E. Parasitism

  • Is a form of symbiosis in which one organism benefits and the other is harmed.
  • An example of parasitism is wasp’s eggs and caterpillar.
  • When the eggs hatch into young wasps, these young wasps burrow into the body of the caterpillar.
  • The young wasps feed on the caterpillar’s tissues. After a month or so, the young wasps chew their way out of the dying
  • caterpillar’s body and spin cocoons.
  • Afterward, the young wasps become adult wasps.
  • This is parasitism because the caterpillar is harmed while the young wasps benefit from feeding on the caterpillar.
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