Beauveria bassiana
Kelly Herrington

Beauveria bassiana is a fungal pathogen that was discovered by Agostino Bassi de Lodi in 1835. Bassi was researching the heavy decline in larval silkworms, which are used to produce silk. He determined that the “muscardine” was caused by a fungus that multiplied in and on the host (Mahr). This was actually the first reported microorganism to be recognized as a contagious agent of animal disease. This pathogen was later named after Agostino Bassi himself, who was also deemed the “Father of Insect Pathology.”

Beauveria bassiana has a variety of characteristics that make it unique to other pathogens. It occurs naturally in soils throughout the world. It produces sexually and asexually. It is usually filamentous and has definite cell walls. The growth rate is moderately rapid. The colonies can reach a diameter of 3 cm following an incubation time of seven days at 27 degrees Celsius on potato glucose agar. It possesses many strains that exhibit considerable variation in virulence, pathogenicity and host range. Beauveria bassiana also has no preference as to its host’s stage in life; it will attack larvae and adults. A very unique characteristic is that it affects its host upon contact, unlike many other pathogens that need to be consumed to cause infection. Upon contact the pathogen kills the host from the inside out. It produces spores, known as conidia (asexual form), that directly infect through the outside of the insect’s skin; it then proceeds to germinate. From the spores it secretes enzymes that attack and dissolve the cuticle. It also produces Beauvericin, a toxin that weakens the host’s immune system. At this point, the fungus is replicating and feeding on the host’s internal organs and blood-like fluids. The host dies within three to seven days after contact. The time variance depends upon the size and complexity of the host. It was generally reported that high humidity and high temperatures are required for the fungus to germinate, but again, it depends upon the host. After death occurs, the fungus proceeds to grow off the host producing a “white bloom” effect. The insect is covered by a white to yellowish cottony/mealy mold layer. The conidia spores are then released into the environment and the life cycle is complete.

Beauveria bassiana is currently being used as an insecticide to control pest populations. A few of these pests include termites, fire ants, whiteflies, aphids and various beetles; the host range list goes way beyond the examples listed here. This fungal pathogen is also under current research and its affects upon the malaria spreading mosquitoes. They intend to spray the mosquito nets with Beauveria bassiana in an insecticide form, therefore upon contact with the nets the mosquitoes will die shortly thereafter; and the hope is to have an eventual decline in malaria. I was unable to find any results with experiment; however I do hope it proves to be successful.

Since Beauveria bassiana is a fungal pathogen, it does not harm humans. One study did show that it may cause keratitis in humans, which is a form of the herpes simplex virus, but no other articles mentioned any side effects. The Beauvericin toxin also proved to show no infections or side effects in laboratory animals.

I was very intrigued by my pathogen after researching it. I find it hard to believe that such a tiny microorganism can cause death to such a wide variety of hosts in such a short amount of time. I have never seen anything like the “white bloom” affect, the pictures I provided in the presentation give more credit to it rather than a simple description. I was also interested in the fact that it could prove to be a positive affect on malaria.

References

Doctor Fungus. “Beauveria bassianahttp://www.doctorfungus.org/thefungi/beauv eria.htm

IPM of Alaska. “Microbial Insecticide: Beauveria bassiana http://ipmofalaska.homestead.com/files/bea uveria.html

Mahr, Susan. “The Entomopathogen Beauveria bassiana” Midwest Biological Control News. http://www.entomolgy.wisc.edu/mbcn/kyf410.html

Technical Bulletin 218 - Fungal Diseases. http://msucares.com/pubs/techbulletins/tb218funga l.htm

Wikipedia .http://en.wikipedia.org/wiki/Beauveria_bassiana

*Disclaimer - This report was written by a student participaring in a microbiology course at the Missouri University of Science and Technology. The accuracy of the contents of this report is not guaranteed and it is recommended that you seek additional sources of information to verify the contents.

 

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