The Middletown Press (Middletown, CT)
Scientists develop germ-free mosquito
New tool for researchers in the fight against diseases
NEW HAVEN — About half of the cells in our bodies don’t genetically belong to us at all.
They’re the bacteria in our digestive tract, on our skin and in a few other places, and they help us digest our food, manufacture vitamins, fight off fungal diseases and in general, keep us on an even keel.
Just about all other animals are loaded with bacteria, too. Take mosquitoes, for instance. Just like in humans, their gut bacteria has similar beneficial traits.
Now scientists at the Connecticut Agricultural Experiment Station have figured out how to raise colonies of germ-free mosquitoes to better understand how the insect transmits deadly pathogens.
It turns out the flora of tiny living things inside the gut plays a key role in the way mosquitoes harbor the dozens of diseases that they’re known for carrying: everything from Eastern equine encephalitis to yellow fever. So by raising germ-free mosquitoes, scientists can better understand the mosquito’s complex relationship with disease organisms and perhaps even develop novel ways of eradicating the pathogens.
As with humans, mosquitoes are germ-free — the scientific term is axenic — before birth. And just like humans, they become inoculated with bacteria as soon as they greet the world.
Fortunately for the researchers, mosquitoes are robust little creatures, so the surface of their eggs can be made germ-free with an application of some common disinfectants — alcohol and bleach.
After hatching, mosquitoes in the wild begin their brief lives as aquatic larva, twitching this way and that in water. Then they enter a pupa stage, which lasts for two days. When ready, the pupa floats to the surface, its back splits open and the adult emerges, the females flying off in search of a first blood meal. Males usually consume only plant nectar.
The challenges for the three Experiment Station scientists — Doug Brackney, Maria Correa and Blaire Steven — were not only to sterilize the eggs, but to raise them in a germfree lab environment. Since gut bacteria is important to the way the insects absorb nutrients, the researchers had to hit on the right combination of food that was both easy to digest and nutritious, and settled on agar — a type of gelatin — and dead bacteria.
After becoming adults, the germ-free diet is maintained with sterilized blood.
The trio expect the germless mosquitoes will find their way into other research as well. Scientists are always looking for inexpensive organisms to experiment on and the mosquitoes can be raised in huge numbers on the cheap.
“You can’t raise axenic humans, obviously,” Steven said. “Yale has axenic mice, but they’re really expensive to raise.”
While mice are a lot closer genetically to humans, mosquitoes have more DNA in common with humans than most people are comfortable with — something on the order of 60 percent.
The two entities share many of the same tissues and organs as well as a segmented body plan, similar nervous systems, two eyes, almost identical metabolisms — the list goes on. Both humans and mosquitoes belong to the same huge grouping of animals known as bilateria — those with a mouth, an anus and a gut in between.
Mosquitoes have been around for more than 75 million years, and were likely making life miserable for dinosaurs and scores of other long-extinct creatures. They’re known to feed on just about any animal with blood, although different species specialize on one host or another. Even the human-feeding ones, such as Culex pipiens, seem to prefer some humans over others.
So can the research be used to wipe out all mosquitoes?
“That would be a very bad idea with huge numbers of unintended consequences,” Steven said. “They’re near the bottom of the food chain, so right away you’d see a number of fish species dying off.”
“Plus there’s about 2,500 known species of mosquitoes — only a handful of which are vectors for disease,” Brackney said.