Gut Microbes Can Evolve From Foe to Friend—And Do It Fast

March 30, 2016 in News by RBN Staff


Not Exactly Rocket Science
 | A Blog by Ed Yong

Bacteria grow quickly, and can evolve quickly.

Bacteria grow quickly, and can evolve quickly. PHOTOGRAPH BY HANSN/FLICKR

 

Dangerous microbes can evolve rapidly. When we throw antibiotics at them, new strains can quickly shrug off the drugs and cause untreatable cases of tuberculosis, gonorrhoea, or staph. But most microbes don’t cause disease. Many share our bodies and those of other animals, and these residents—our so-called microbiome—are important parts of our lives.

And they can evolve too.

A microbe can even evolve quickly from a parasite into an allyKayla King from the University of Oxford found an excellent example of this in the guts of nematode worms. She showed that a bacterium called Enterococcus faecalis, which causes mild disease, can suddenly turn into a protector if its host is challenged by another more dangerous threat, Staphylococcus aureus or Staph.

King began by infecting worms with either Enterococcus or Staph. The two microbes behaved very differently. Enterococcus caused mild infections, killing fewer than one in a hundred worms, and only then after a week. By contrast, Staph killed half the worms within a day and all of the after a second. When mixed, Enterococcus protected the worms from its more virulent peer, slashing the death rate from 52 percent to just 18 percent.

To see if this dynamic would change over time, King picked out some infected worms, removed Enterococcus from their bodies, grew the microbes up, and then fed them to another generation of worms. She repeated 15 times. And in each new round she added the Enterococcus to genetically identical worms from the same stock, along with the same strains of Staph.

By the experiment’s end, Enterococcus had become an exceptional guardian, saving all but one percent of its hosts. It had evolved the ability to produce large amounts of superoxides—highly reactive oxygen molecules that are toxic to many microbes, Staph included. Enterococcus, by poisoning its rivals, was saving the worms.

This change depended entirely on the presence of Staph. When King exposed 15 generations of worms to Enterococcus alone, the mildly harmful bacterium became slightly more harmful. “On its own, it’s a little bit of a parasite,” says King. “But when it interacts with this much more virulent organism, it shifts along the continuum to be much more beneficial.”

She was surprised at how quickly the protective powers evolved (within just five of the 15 generations), how total they were (almost all the worms survived), and how broad it was. She challenged the worms with seven different strains of Staph, including the drug-resistant MRSA strains that give us humans so much grief. The protective Enterococcus strains beat them all.

There are many examples of microbes protecting animal hosts from parasites and diseases by producing antibiotics. …. CLICK HERE TO READ MORE