NARRATOR: This ecology experiment is one of many that have demonstrated how ecosystems with many species tend to be more resilient than those with few species. We're biased towards this particular grassland experiment because it's run by one of our writers, but strength in species numbers is also key to the health of ecosystems ranging from potato fields to rivers to the inside of your gut.
In contrast, when a single species is dominant, it can cause problems. Take the case of Clostridium difficile, a natural part of your gut community that causes a severe inflammation of the colon when it becomes too abundant. This bacteria, often referred to as "C diff", was named "difficile" because it was difficult to grow in a lab, not because it's difficult to treat. But it is. C diff infections often develop because these bacteria persist better and regenerate faster than other gut bacteria following an antibiotic treatment for some unrelated health problem.
Ironically, the standard treatment for C diff is yet more antibiotics—which sometimes works, but in many cases the antibiotic resistance of C diff means the playing field is simply cleared of its competitors, and its population can grow even more vigorously.
So vigorously, in fact, that of the roughly 500,000 people infected each year in the US, about one in 30 die as a result, even after further drug treatments or surgery to remove parts of the colon. Out of desperation came the idea to entirely replenish the gut microbiome—not with probiotics, which only supply something like 1 living organism for every 10,000 bacterial cells already in your gut and just aren't powerful enough to make a difference, but, rather, with something more like the microbial equivalent of a blood transfusion. And just like a blood transfusion, don't try this at home!
In a "fecal microbiota transplantation", or "poop transplant", someone with a healthy, diverse community of gut bacteria donates a sample to be administered to a patient with a C diff infection. And in about 400 of 470 documented cases, the transplanted bacterial community quickly became dominant, causing the patient's digestive system to recover and stabilise. Though scientists still don't know exactly how that happens.
The human gut isn't the only ecosystem where this germ of an idea is taking hold, either. For example, transplanting soil from healthy fields to unhealthy ones helps knock back crop diseases and make soils more fertile; and transplanting water, snails and duckweed from a pond to an aquarium helps maintain a well-balanced fishtank.
At the moment, microbial transplant therapy for disease control resides at the fringes of medicine, agriculture, and home fishtank husbandry. For medicine, this may in part be due to people being squeamish about their own, and others', fecal matter, and insurance companies being squeamish about covering the cost of the procedure. But money also plays a broader role: new practices—even really good ones—have difficulty spreading without active promotion, and that promotion often comes from places like the pharmaceutical, agrochemical and home aquarium industries—industries which promote only those things from which they can make a profit, like drugs, fertilisers, aquarium supplements, and other heavily-engineered chemical cocktails.
But who will promote the simple solutions? We will! For your C. diff to recoup, choose someone else's poop.