The Research column will be a weekly feature on the scientific opportunities on campus written by staff writer Diler Haji.
The science of symbiosis is booming. For so long, we’ve attacked bacteria, viruses and other pathogens relentlessly in the hope of curing the poster-child of human suffering — disease.
These culprits aren’t exactly welcomed companions in our societies. In fact, we destroy them with an onslaught of antibiotics and hand sanitizer every day.
You may be surprised to discover that among all the bacteria on Earth, less than 1 percent are actually the cause of disease. Many of them are symbionts; partners in a bond that allow them and their hosts to coexist and prosper. These symbionts aren’t just found lining our guts and coating our skin, but throughout the animal kingdom and particularly within those tiny blood-suckers responsible for more human death than any war.
I’m referring to mosquitoes, tsetse flies, sand flies, ticks and many more insects that act as vehicles of disease. If you were a pathogen (disease-causing organism) and your life depended on infecting a mammal (let’s say a human), then hitching a ride through the body of a small insect is your best bet.
Humans contain billions of symbiotic bacteria that represent thousands of different species. Such a complex world can’t be easy for a pathogen to traverse. Even if the pathogen found a way, it would have to get through our immune system, which seeks and destroys intruders that dare enter our bloodstream.
Scientists are increasingly discovering that our symbionts boost our immune system, making us much better at hunting down those intruders.
Ironically, our immune system still has to be alert. After all, there are millions of bacteria swimming around inside of us and while they are beneficial in our gut, they will quickly become pathogenic (disease-causing) if they found a way into our blood — this is called sepsis.
For a pathogen from the outside looking in, the bite of a mosquito, tsetse fly or tick is a straight shot into human blood. These insects are programmed to pinpoint large, warm-blooded mammals like us for food.
All the pathogen has to do is infect an insect.
But just like humans, insects have symbionts too. Those symbionts protect them from pathogenic intruders by boosting their immune system (just like us). In fact, a recent study on tsetse flies, the insect responsible for African sleeping sickness, in eLife by Joshua Benoit and colleagues showed that a certain symbiont by the name of Wigglesworthia is literally a life saver.
Somehow, Wigglesworthia drastically increases the tsetse’s ability to produce crystal cells, a vital immune system “soldier” found across the animal kingdom, including humans. When Wigglesworthia was separated from the tsetse, the fly was nearly stripped of its ability to produce the crystal cells it needs to fight off pathogenic intruders.
It’s no surprise that over the course of evolution, tsetse flies have gained an entire organ attached to their gut specifically designed to house Wigglesworthia. They even pass the symbiont down through milk they feed a baby tsetse that grows up inside of them — this is completely odd among insects and, frankly, seems like something from an alien world.
It seems that without its symbiont, tsetse is much more likely to be infected by the bug that caused African sleeping sickness.
Once tsetse bites into a human, it transmits the bug and triggers a cascade of horrifying symptoms — joint pain, itching and headaches at first, then changes in behavior and coordination as the disease get into the brain.
Finally, infected patients lapse into a coma and seldom awake — hence, why it’s called sleeping sickness.
Thanks to a rise in symbiont research, we may have a way of controlling horrible diseases like African sleeping sickness, Chagas disease, Dengue fever or even malaria.
We’ve tried destroying the insects that carry those diseases with chemicals like DDT, but that approach backfired because it threatened our health and our pollinators. We’ve even tried releasing "sperm-less” males in the hope of tricking females into producing dead babies. These efforts haven’t exactly solved the issue.
Through paratrangenesis, researchers hope to genetically modify symbionts so that they can help their insect hosts resist pathogens — it’s essentially fighting infection with infection!
Once infected by the modified symbiont, the insect will pass it down through the generations, preventing certain diseases from spreading in the future.
This is the subject of ongoing research interest and it couldn’t be possible without understanding symbionts. It’s increasingly becoming clear that a huge part of animal life involves the non-animal life we can’t see. Teasing out those interactions is key to both filling knowledge gaps in biology and saving lives.
Bacteria, viruses and other microorganisms often have two faces, but we can’t protect ourselves by seeing just the bad face – we need to understand the good.
Diler Haji is a staff writer for The Daily Campus. He can be reached via email at firstname.lastname@example.org.