Metarhizium anisopliae

Metarhizium anisopliae, formerly known as Entomophthora anisopliae, is a fungus that grows naturally in soils throughout the world and causes disease in various insects by acting as a parasite; it thus belongs to the entomopathogenic fungi. It is known to infect over 200 insect species, including termites. It is currently being used as a biological insecticide to control a number of pests such as grasshoppers, termites, thrips, etc. and its use in the control of malaria-transmitting mosquitos is under investigation.

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The disease caused by the fungus is called green muscardine disease because of the green color of its spores. When these mitotic (asexual) spores (properly called conidia) of the fungus come into contact with the body of an insect host by entering through the spiracles and pores of the host's sense organs, they germinate and the hyphae that emerge penetrate the cuticle. The fungus then develops inside the body eventually killing the insect after a few days; this lethal effect is very likely aided by the production of insecticidal cyclic peptides (destruxins). The cuticle of the cadaver often becomes red. If the ambient humidity is high enough, a white mold then grows on the cadaver that soon turns green as spores are produced. Most insects living near the soil have evolved natural defenses against entomopathogenic fungi like M. anisopliae. This fungus is therefore locked in an evolutionary battle to overcome these defenses, which has led to a large number of strains that are adapted to certain groups of insects. Some strains are so specific that they have attained variety status, like Metarhizium anisopliae var. acridum, which almost exclusively infects grasshoppers in the suborder Caelifera of the Orthoptera.

The fungus does not appear to infect humans or other animals and is considered safe as an insecticide. The microscopic spores are typically sprayed on affected areas; the plan for malaria control is to coat mosquito nets or cotton sheets attached to the wall with them. The level of insect control (mortality) in general depends on factors like the number of spores applied against the insect host, the fungus strain used, the formulation and weather conditions. Oil-based formulations allow the application of fungal spores under dry conditions.

Metarhizium anisopliae was named after the insect species it was originally isolated from, the beetle Anisoplia austriaca. It is a mitosporic fungus with asexual reproduction for which a teleomorph has not yet been discovered. Cordyceps taii was shown to be the teleomorph of Metarhizium taii, so it seems likely that the one of M. anisopliae will also turn out to be a Cordyceps species. However, it is also possible that some, if not most, strains of M. anisopliae have lost the capability of reproducing sexually.

In August 2007, a team of scientists at the Indian Institute of Chemical Technology discovered a more efficient way of producing biodiesel which uses lipase, an enzyme produced in significant quantities by Metarhizium anisopliae; as opposed to other reactions which use enzymes that require heat in order to become active, the reaction that uses lipase runs at room temperature. The fungus is now a candidate for mass production of the enzyme.

See also

• Beauveria bassiana, the fungus that causes white muscardine disease in various insects

References

• F. Driver, R. J. Milner, W. H. Trueman (2000). "A Taxonomic revision of Metarhizium based on sequence analysis of ribosomal DNA". Mycological Research 104: 135-151.
• C. J. Lomer, C. Prior, C. Kooyman (1997). "Development of Metarhizium spp. for the control of grasshoppers and locusts". Memoirs of the Entomological Society of Canada 171: 265-286.
• Donald G. McNeil Jr., Fungus Fatal to Mosquito May Aid Global War on Malaria, The New York Times, 10 June 2005
• Screen, S.E., Hu, G. and St. Leger, R. J. 2002. Transformants of Metarhizium anisopliae sf. anisopliae overexpressing chitinase from Metarhizium anisopliae sf. acridum show early induction of native chitinase but are not altered in pathogenicity to Manduca sexta . Journal of Invertebrate Pathology 78: 260-266.
• Freimoser, F. M., Screen, S., Bagga, S., Hu, G and St. Leger, R.J. 2003. EST analysis of two subspecies of Metarhizium anisopliae reveals a plethora of secreted proteins with potential activity in insect hosts. Microbiology 149: 239-247.
• Aaron Rowe, Fungi Make Biodiesel Efficiently at Room Temperature, Wired Science, 20 August 2007
• Raymond A. Cloyd, The Entomopathogenic Fungus Metarhizium anisopliae, Midwest Biological Control News, Vol VI No 7