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Invisible Companions: Scientists Begin To Uncover How Bacteria Strike Up Friendly Relationships

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Bacteria are everywhere—throughout our bodies, in the air, and even part of some of the foods we eat, like yogurt. The ubiquitous nature of microbes may be unnerving to some, since these microscopic creatures don’t have a squeaky clean record. Some do cause disease, but the good they bring to the world often goes unnoticed.

“I think the sense still is that microbes have a bad rap. Everybody’s running around with hand sanitizer and little bit concerned about being contaminated by microbes,” said Colin Dale, an associate professor of biology at the University of Utah. “What we’re seeing now [though] is that microbes also play a very beneficial role in our world.”

A new study by Dale and his colleagues showcases the better side of bacteria and provides insight into how how these microscopic critters form friendly relationships with other organisms.

“We study insects, because they are relatively simplistic in nature,” said Dale. “Unlike humans, which harbor, literally, millions of different types of microbes, insects tend to have just one or two.”

Dale added that insects often harbor the same bacterial species, raising the question of what it is about these particular microbes that promotes a friendly association with insects.

“What we’ve found is that they are special in the way they treat their insect host,” Dale said.  

The bacteria produce virulence factors—think of these as ammunition—that allow the microbes to break into the insect tissues and establish a home. Surprisingly, these friendly microbes invade the host like pathogenic (disease-causing) bacteria do.

“What makes them different from pathogens,” said Dale, “is that once they're in the host, they can sense they’ve made it using a special sensing system.”

Once the friendly bacteria get inside the insect, they get rid of their ammunition and maintain a benign relationship with their host. The pathogens we are all familiar with do the opposite. They start acquiring more ammunition to make you sick.

So, how do the friendly bacteria know to start being nice and halt production of their ammunition? Well, the microbes communicate.

“They do this by secreting a chemical hormone,” said Dale, “and this hormone increases in concentration as bacteria increase in a given environment. The cells can use a special protein to read the concentration. When this hormone reaches a critical threshold, the bacteria sense it using that special protein and that protein turns off the expression of the virulence genes.”

Ultimately, no more ammunition is made, and a beneficial relationship is born. The friendly microbes can produce nutrients in the form of vitamins or amino acids for their insect host and even defend against parasites. And, it should be noted the microbe doesn’t have it too bad either.

“The host environment is full of nutrients. This is a very cushy life for any microbe,” said Dale, “and it’s a life that’s free of competition. If you can get into a host and make that host successful, that host will look after you. In a way, it’s immortalization.”

Perhaps, most microbes shouldn’t get a bad rap after all. 

“I think in the near future, our perception of microbes is going to change from the pathogen dominated view that we’ve had,” said Dale. “Hopefully, we’re going to embrace them a little bit more.”