Antimalarial fungi
Transgenic fungi helped in the fight against malaria
The researchers used the fungus Metarhizium pingshaense to fight malaria, some strains of which can infect malaria mosquitoes. To enhance the virulence of the fungus, its genome was modified by embedding an insect-specific toxin gene. The results of a study published in the journal Science (Lovett et al., Transgenic Metarhizium rapidly kills mosquitoes in a malaria-endemic region of Burkina Faso) suggest that this method, even with small concentrations of fungal spores, is effective in conditions as close as possible to the present.
Today, the main means to combat malaria are insecticides that act on mosquitoes. Unfortunately, recently mosquitoes are beginning to acquire resistance to these substances, so the search for alternative or additional ways to reduce the incidence is quite relevant.
The larva of the beetle Dermolepida albohirtum, affected by a fungus from the genus Metarhizium. A snapshot from the CSIRO website.
Metarhizium pingshaense spores have already been sprayed inside huts in malaria foci in Tanzania. This really reduces the number of bites by infected mosquitoes, but the strain used is still not aggressive enough to achieve the goal.
Last year, a joint group of scientists from the United States and Burkina Faso decided to improve the fungus by adding a gene of the Hybrid toxin, dangerous for insects, to its genome. They conducted laboratory studies in which the high potential of the modified fungus was demonstrated. Nevertheless, successful tools in the laboratory often turn out to be powerless in real conditions, so in the new work, the researchers tried to bring the test conditions as close as possible to the real ones.
An experimental site with huts, mosquito nets between the cells have been removed. Here and below are drawings from an article in Science.
Brian Lovett from The University of Maryland and his colleagues chose a place near a malaria-endemic village in Burkina Faso and installed cameras there, separated from each other and from the external environment by a mosquito net. Inside four of them, analogues of the huts of local residents, a source of sugar for adult mosquitoes and breeding grounds were installed, which were plastic pallets covered with a layer of earth that allowed moisture to accumulate. After that, the researchers collected larvae of malaria mosquitoes resistant to conventional insecticides, raised them and launched them into experimental huts, for a start, 100 females each. Inside the huts, among other things, there were calves (as a source of blood for mosquitoes) and black cloths of cloth on which oil was applied with spores of a GM fungus with an embedded toxin gene (Mp-Hybrid) or a control fungus with an embedded insect-friendly red fluorescent protein (Mp-RFP), or empty oil. The experiment began at dusk, and in the morning all the mosquitoes were caught back and checked for the presence of a fungal infection. In total, the researchers made seven replicas of the experiment, during which 2402 mosquitoes were caught back. The best place to catch were black cloths (43.5 percent of mosquitoes), on which mosquitoes rested after eating, and the second most popular place was the ceiling of huts (27.3 percent). These results did not depend on what the canvases were impregnated with, so the authors concluded that fungi do not scare away resting mosquitoes.
After checking for infection, it turned out that 79 and 72 percent of mosquitoes from huts with canvases with spores were infected with Mp-Hybrid and Mp-RFP, respectively; as a result, the insects died. The control population of mosquitoes from huts without fungal spores decreased slightly.
Survival of mosquitoes after being in control huts without fungal spores (blue), with control fungal spores (red) and with toxin-expressing fungal spores (green).
In the next series of experiments, the researchers looked at how the presence of the fungus would affect the population of mosquitoes populated in the chambers. To do this, they released 1,000 male and 500 female mosquitoes into each chamber, and then monitored the number of adults, eggs, larvae and pupae for 45 days, periodically launching calves into the hut. This time covers the life of about two generations of mosquitoes and the researchers showed that, unlike control experiments in cameras with Mp-Hybrid, the mosquito population collapsed quite quickly.
Three replicas of the experiment on the dynamics of the number of mosquitoes (from top to bottom), where the number of adult individuals in each variant of the experiment is shown by lines of different colors (blue – without fungus, red – with a control GM fungus with RFP, green – with a GM fungus with toxin).
Thus, the authors showed that inserting the gene of the corresponding toxin into the fungus greatly increases its natural virulence and demonstrated the effectiveness of such a method in conditions as close to real as possible.
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