MICROBIAL INTERACTIONS

BY: SAI MANOGNA (MSIWM014)

Biological interactions are the impact that species in the environment have on each other

• The interactions between different microbes, plant and germ interactions to promote growth, animal interactions, interactions with human beings and water interactions occur in a whole range of microbes.
• In any biological culture, microbial interactions are all distinctive, complex, critically important and are central in global biogeochemistry.
• The relationships between these two populations are defined by whether the relations favour both populations and benefit one of them, or whether one or both populations are negatively affected

Microbial interactions are of two types :

1. Positive Interactions : Mutualism, Syntrophism, Photoreception, Commensalism.
2. Negative Interactions : Ammensalism (antagonism), Parasitism, Predation, Competition.

Positive Interactions :

1. Mutualism : Mutualism is defined as interactions between organisms of two different species, in which each organism benefits in some way from interactions.

    i. These types of interactions are common and ubiquitous across all ecosystems, and scientists increasingly recognise the important role they play in ecology.

    ii. Mutualisms are also symbiotic partnerships. In such situations, the two animals live in close proximity to each other for part or all their whole lives; however, not all symbiotic relationships are reciprocal.

Examples of Mutualism:

Several known examples of mutualistic arrangements exist.

1. Nitrogen fixing bacteria and Leguminous Plants : The relationship between nitrogen-fixing bacteria and leguminous plants

• Intestinal flagellates and Termites : Intestinal flagellates and termites exhibit obligate mutualism, a strict interdependence in which protozoans digest the wood eaten by termites; Here neither partner can live under natural circumstances without the other.

• Yucca Moths (Tegeticula) and Yucca Plants : Yucca moths depend on yucca plants and the other way around. The moth goes about as a pollinator while laying her eggs in yucca seed pods. The hatchlings incubate and feed on a few yet not all seeds. Here the two species have advantages such that the plant is pollinated and the moth has nourishment for its hatchlings.

II. Syntrophism : Syntrophy is the mutual dependency of various types of species on the fulfilment of their respective nutritional needs. The intermediate or end products metabolism of one organism are important materials for another. Syntrophism is exemplified in the mixed environment population.

Examples of Syntrophism:

1. Dust mites on Human Skin : House dust mites fleece human skin. A healthy person produces about 1 gram of skin flakes daily. These mites may also produce chemicals that stimulate skin flakes. People may become allergic to these compounds.

• Organisms on cow-dung : A cow eats lots of grass, which is converted into lipids by microorganisms in the large intestine of the cow.

III. Photoreception : It is a relationship in which the organisms are mutually beneficial and in association with each other. This relationship is similar to mutualism, but relations between the species in proto-cooperation are not necessary as in mutualism.

Examples of Photoreception :

1. Interaction of Nitrogen fixing bacteria and Cellulomonas :

IV. Commensalism : In Biology,commensalism refers to the relationship between two species in which one species, without harming or helping the latter, obtains food or another benefits from the other.

    i. The species i.e, benefiting from the unaffected species (host), can obtain nutrients, shelter, protection or locomotion.

   ii. The relationship is predominantly between the larger host and the smaller commensal. In essence the host organism remains unchanged through contact, while the commensal species can exhibit great morphological adaptation.

Examples of Commensalism :

1. Shark and Remora : remora attaches to the shark or other fish and rides on it. Remoras evolved on their heads as a flat oval shaped disc structure that adheres to their host bodies.

Negative Interactions :

1. Ammensalism : Ammensalism is any relationship between two different species, where one organism is inhibited or eliminated, while the other remains consistent.

     i. One microbial population develops substances that are inhibitory to the other microbial populations which is antagonistic known as ammensalism are antagonism.

   ii. In nature, no organism can live its life in complete isolation. They must communicate in some way with other species and their environment.

Examples of Ammensalism : There are basically two types 1. Competition 2. antibiosis.

1. Competition : A Larger more potent organism removes another organism from its source of food and shelter.
2. Antibiosis : One organism secretes a chemical that destroys the other organism, but the one which secretes the chemical is unharmed.

       Example : penicillium on black walnut trees : The Mould that is capable of producing penicillin, which kills several types of bacteria that would also like to grow on this bread. The bacteria killing effects of penicillin that contributed to the use of penicillin as antibiotic. Penicillin doesn’t benefit from the death of other bacteria, making it an example of amensal antibiosis.

 II.  Parasitism : Parasitism is a relationship between two separate species, where one of them actually affects the other. An organism that harms the other is considered a parasite.

   i. The host-parasite relationship is characterised by a relatively prolonged period of interaction that may be physical or metabolic.

   ii. Some parasites live outside the host cell, known as ectoparasite, while others live within the host cell, known as endoparasite.

Examples of Parasitism :

1. Ticks on Dogs and cats : Fleas or ticks that adhere to the skin of dogs and cats are parasites.

• Lice :  This is another parasite that lives off the blood of host animals.
• Aphids : Aphids are a type of insect parasite that feeds on the sap of host plants.

III. Predation : Predation refers to the relationship between organisms in which one organism kills and devours another.

   i. Predation gives energy to prolong life and to facilitate the reproduction of the organism that destroys the predator, to the detriment of the organism that is eaten, the prey.

  ii. Predation affects species in two ecological states.

  iii. At the level of an individual, the prey organism has a sharp decline in fitness as calculated by its lifetime productive success, since it can never produce again.

  iv. At the group level, predation decreases the number of individuals in the population of prey.

Examples of Predation :

1. Carnivorous interactions :  The best known examples are Wolves hunting moose, Frogs eating flies, Owls hunting mice, Shrews hunting worms or insects.
2. Group Predation : This occurs with ants and social spiders.

IV.  Competition : A Larger more potent organism removes another organism from its source of food and shelter.

  i. This interaction occurs when both species (populations) use the same resources, resulting in lower maximum density or growth rate for the microbial population.

Examples of Competition :

a. Competition between Paramecium caudatum and Paramecium aurelia : When these protozoa are brought together, both paramecium species feed on the same bacterial community.