When Evolution Is Infectious: How “probiotic epidemics” help wildlife—and us—survive

Moises Velasquez-Manoff in Nautilus:

Ever since Charles Darwin taught us that life is constantly driven to change by myriad pressures—that species are not static, but are constantly morphing—biologists have debated how fast those changes can occur. The discovery of the genome a century after Darwin published On the Origin of Species seemed to demarcate an upper limit. Animals could evolve only as fast as advantageous genes could arise and spread, and as existing genomes could be reshuffled through sexual reproduction. But then came “epigenetics”: Some adaptation could occur more quickly, without changing genes themselves, but by altering how existing genes translated into living flesh. Rosenberg and others are proposing an even quicker process—organisms can adapt rapidly by switching their symbiotic microbes. The very quality that makes pandemics so terrifying—rapid contagion—may also drive mass adaptation.

To support the hologenome theory, Rosenberg and others look to the study of the human microbiome, particularly the example of Clostridium difficile. People tend to acquire the bacterium during hospital stays and after they’ve “clearcut” their native microbes with antibiotics directed at another infection. C. difficile then blooms. Patients can end up delirious and in pain, weakened by an unremitting torrent of bloody diarrhea. The microbe infects an estimated 500,000 Americans yearly, killing some 29,000 of them within a month.

C. difficile is increasingly resistant to antibiotics, so further treatment fails in about 1 in 5 cases. For this subset, the “fecal transplant” is nearly miraculous. The procedure involves “implanting” stool from a healthy person, via enema, or in pills, into the intestines of one stricken with C. difficile. And it’s 94 percent effective at curing C. difficile. It works, scientists think, by restoring a fully functioning microbial ecosystem in one fell swoop. The donor’s tight-knit community deprives the pathogen C. difficile of an ecological niche, squeezing it from the gut. Technically, stool transplants are not “probiotic epidemics.” But the principle the transplant illustrates—that native microbes prevent disease, and that tweaking those microbes can fend off a deadly infection—is precisely what scientists think could drive a probiotic epidemic.

More here.