Parasitism

Parasitism

Parasitism
It is a negative interaction wherein one population is adversely affected by the other. It is a long-term interaction and maintains a physical or metabolical contact. Parasites are the organisms which eventually kill one population (host) and they can be either attached outside the host (ectoparasite) or can be found within the host (endoparasite). Normally, parasitic interactions are very specific. A very good example for this kind of interaction is the virus population that parasitises a range of hosts like bacteria (bacteriophage), algae (phycophages), fungi (mycophages), actinomycetes (actinophages). A bacterium Bdellovibrio is ectoparasitic on several gram negative bacteria.

Interaction occurs for one hour during which the host cell loses its shape and becomes spherical (bdelloplast). Other microbes cause lysis without direct contact. For example, Myxobacteria causes lysis of susceptible microorganisms with the help of exoenzymes. Some bacterial population produce chitinase which lyse the fungal cells. Protozoans are subjected to parasitism by fungi, bacteria and protozoa themselves. Algae are attacked by fungi (chitrids). Fungi attack fungi as seen in Agaricus being parasitised by Trichoderma species. Microorganisms that are themselves parasites may serve as a host for other parasites (hyperparasitism). For example, Bdellovibrio which is itself a parasite serves as a host for the phages. Thus parasitism provides a mechanism for population control and is density dependent, i.e. parasites can thrive only as long as the host survives.

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