Insect-Microbe Symbiosis

Insect-Microbe Symbiosis

	Insect-Microbe Symbiosis There are other mutualistic relationships in food digestion in the form of intestinal symbionts or as a directed external cultivation of microbial biomass for subsequent consumption. Several insects actually cultivate pure cultures of microbes on plant tissues in a mutualistic relationship.
Various leaf-cutting ant populations maintain mutualistic relationships with fungi. The ants supply leaf tissue for the microbes by inoculating segments of the leaves, and shield the cultivated fungus from competitors maintaining a virtual monoculture that breaks down rapidly if the cultivating ants are removed. For example, Atta species of ants cultivate Agaricus. Myricocrypta buenzlii (attine ants) cultivate Lepiota (fungal) species.
Attine ants are important because they are responsible for introducing large amounts of organic matter into the soil in rainforests. In the case of the fungus cultivated by attine species of ants the fungus is deficient in proteases and competes poorly with other fungi if not under cultivation by the ants. This particular species of ants chews off sections of green leaves and carries them to a nest where the collected leaves are coated with saliva, cut up into pieces a few millimetres across and wetted with drops of liquid from the anus of the ants. These processes remove or prevent the growth of foreign microorganisms.
The prepared leaves are inoculated with pure cultures of fungi (Lepiota) which were originally brought by the fertile queen who founded the colony from her home nest. The fungus is grown in pure culture on the leaves even though it is surrounded by soil and the ants bring in many microorganisms from their foraging expeditions. The ants constantly clean their nests, themselves, weed their garden and deposit anal drops onto it. This is done to sterilise their surroundings including themselves and even if any foreign microbe is detected, it is prevented from growing due to the presence of antibiotics in the saliva, and the anal fluid takes care of any that may get through the cleaning.
	The fungus is the sole food source of the ants and contains a higher percentage of protein than the original leaves. The fungus supplies cellulase to break down the vegetable matter though the ants add proteases, amylases and chitinases (to lyse any foreign fungi) in the anal fluid. The surprising part of the relationship is that most of the fungi are not know to grow outside ants' nest and the fungi enjoy a competition-free life

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