PhysOrg has a report on a genetically modified fungus that is capable, if released into the wild, of using spider venom to eliminate the mosquitoes that carry one of the nastiest diseases out there:
The study showed that a naturally occurring fungus engineered to deliver a toxin to mosquitoes safely reduced mosquito populations by more than 99% in a screen-enclosed, simulated village setting in Burkina Faso, West Africa.
“No transgenic malaria control has come this far down the road toward actual field testing,” said Brian Lovett, a graduate student in UMD’s Department of Entomology and the lead author of the paper. “This paper marks a big step and sets a precedent for this and other transgenic methods to move forward.”
The fungus is a naturally occurring pathogen that infects insects in the wild and kills them slowly. It has been used to control various pests for centuries. The scientists used a strain of the fungus that is specific to mosquitoes and engineered it to produce a toxin that kills mosquitoes more rapidly than they can breed. This transgenic fungus caused mosquito populations in their test site to collapse to unsustainable levels within two generations.
“You can think of the fungus as a hypodermic needle we use to deliver a potent insect-specific toxin into the mosquito,” said [UMD entomologist and study co-author Raymond] St. Leger.
The toxin is an insecticide called Hybrid. It is derived from the venom of the Australian Blue Mountains funnel-web spider and has been approved by the Environmental Protection Agency (EPA) for application directly on crops to control agricultural insect pests.
To modify the fungus Metarhizium pingshaense so that it would produce and deliver Hybrid, the University of Maryland research team used a standard method that employs a bacterium to intentionally transfer DNA into fungi. The DNA the scientists designed and introduced into the fungi provided the blueprints for making Hybrid along with a control switch that tells the fungus when to make the toxin.
The control switch is a copy of the fungus’ own DNA code. Its normal function is to tell the fungus when to build a defensive shell around itself so that it can hide from an insect’s immune system. Building that shell is costly for the fungus, so it only makes the effort when it detects the proper surroundings—inside the bloodstream of a mosquito.
By combining the genetic code for that switch with the code for making Hybrid, the scientists were able to ensure that their modified fungus only produces the toxin inside the body of a mosquito.
In a rural, malaria-endemic area of Burkina Faso, they constructed a roughly 6,550-square-foot, screened-in structure they called MosquitoSphere. Inside, multiple screened chambers contained experimental huts, plants, small mosquito-breeding pools and a food source for the mosquitoes.
In one set of experiments, the researchers hung a black cotton sheet coated with sesame oil on the wall of a hut in each of three chambers. One sheet received oil mixed with the transgenic fungus Metarhizium pingshaense, one received oil with wild-type Metarhizium and one received only sesame oil. Then, they released 1,000 adult male and 500 adult female mosquitoes into each chamber of MosquitoSphere to establish breeding populations. The researchers then counted mosquitoes in each chamber every day for 45 days.
In the chamber containing the sheet treated with the transgenic fungus, mosquito populations plummeted over 45 days to just 13 adult mosquitoes. That is not enough for the males to create a swarm, which is required for mosquitoes to breed. By comparison, the researchers counted 455 mosquitoes in the chamber treated with wild-type fungus and 1,396 mosquitoes in the chamber treated with plain sesame oil after 45 days.
Next, the international team of scientists hope to test their transgenic fungus in a local village or community.
The original study in Science magazine is here.