Most people are familiar with the role of DNA: A set of genetic instructions on how a particular living organism should function. This nucleic acid has been widely explored as a way to identify individuals, define illnesses or hereditary diseases and contribute to behavior, among many other clues about an individual. However, there may be another complex feature of human anatomy that influences many surprising aspects of human physiology, immunity and evolution: gut flora.
Scientists are exploring the ways in which microbial communities inside the gut are unique to each individual. Paths within this area of research have led to, for example, individual gut signatures, species and lineage identification, benefits of group living and even fecal transplants.
Humans acquire gut flora—consisting primarily of bacteria with some fungi and protozoa—from their mothers during birth and later through breast feeding, suckling and caressing. These bacteria inhabit a person’s digestive track for a lifetime and contribute to immunity. As Ed Yong explains in a recent Not Exactly Rocket Science article, these communities continue to adapt as an individual develops and changes the types of food they eat.
As we get older, the bacteria of [humans] change to cope with different sources of food, from the milky diets of babies to the complex carbohydrates of adulthood. As adults, our diet also affects our bowel buddies. In African villages where high-fibre diets are the norm, Humanville is populated by plant-digesting microbes that are relatively rarer in the guts of fat-guzzling Europeans. Diseases, courses of antibiotics and changes in body weight can also shift the balance of the microbiome, causing some members to move in and others to leave.
Research has suggested that microbial communities have evolved with their hosts for millions of years, making these microbiota both species-specific and unique to each individual. That is, similar to tracking someone’s DNA through hair or blood samples, it is possible to identify a person’s gut signature by their feces—a process known as metagenomic sequencing. Gut signatures also reveal the species and lineage of a person or animal. In the same article written by Yong, he writes about Howard Ochman from the University of Arizona who examined the gut flora of gorillas, chimpanzees and other primates. Ochman found that “host species completely overwhelm the influence of things like geography,” writes Yong. “For example, one of the chimp groups lives in the same area as one of the gorillas, but their gut bacteria are only distantly related.”
Gut flora may even play a role in the evolution of communities. Beyond the more prevalent reasons why some animals tend to stick together—such as mutual aid, foraging assistance and decreased risk of predation—a paper published in a 2007 issue of the journal Behavioral Ecology and Sociobiology suggested group life might have other unseen benefits: access to microbes. Michael Lombardo from Grand Valley State University argues that some animal species may have evolved to live in groups to benefit from sharing useful microbes with one another through complex social interactions, such as grooming.
On the other hand, this social structure could also spread harmful viruses and bacteria . Microbial communities help with immunity from virus and bacterial infections. However, if certain bacteria die off, say through the administration of antibiotics, other microbial communities may begin to wreck havoc. This is the case with Pseudomembranous colitis, also known as antibiotic-associated diarrhea (AAD), in which antibiotics wipe out other competing bacteria. This allows the bacterium Clostridium difficile to overrun the colon and create difficult to remove spores.
Sometimes discontinuing antibiotics allows the gut flora to repopulate and restore balance. But in some last resort cases, a fecal transplant—a procedure gaining some ground as a reliable treatment for intractable gastrointestinal problems like AAD— may be required. Fecal transplants, also known as fecal bacteriotherapy and human probiotic infusion, usually involve flushing out the imbalanced colon with enemas and introducing a fecal donation from a healthy relative. The healthy feces is intended to restore the missing microbiota in the colon and reestablish homeostasis, stability in the body’s inner environment.
As bizarre and, frankly, gross as this procedure may sound, it is currently the most effective way to treat AAD sufferers: According to a November 3 article of The Scientist, fecal transplants have a 95 percent cure rate for AAD. Christina Luiggi also mentions in the article that the procedure is gaining ground as a potential treatment for inflammatory bowel diseases and irritable bowel syndrome as well. Luiggi writes about Thomas Borody, director of the Centre for Digestive Diseases in New South Wales, who has had marked success from the approximately 1,500 transplants he has performed:
He treats patients that, in addition to bowel complaints, also have seemingly non-gut related conditions such as chronic fatigue syndrome, acne and multiple sclerosis,” said Luiggi. “And he’s getting some early evidence that, in some cases, the transplant can reverse the symptoms of those accompanying conditions as well.
Researchers such as John Rawls from the University of North Carolina have discovered other connections between gut flora and human conditions by performing fecal transplants across species. Jeffery Gordon from Washington University in St. Louis transplanted human feces into sterile mice and found associations between gut flora and obesity. He has reported on the presence of lean and obese microbiota in his research. As quoted in the article:
It is tempting to think that if you wanted to treat human obesity, that you could do fecal transplants with the microbiota from lean individuals,” Rawls said. But it may be somewhat premature to proceed, he cautioned—”if we don’t understand the rules that govern the establishment and maintenance of those microbial communities in the gut, the effects of other people’s transplants could potentially be short-lived or even deleterious.
Photo Credit: Nephron
Lombardo, M. (2007). Access to mutualistic endosymbiotic microbes: an underappreciated benefit of group living Behavioral Ecology and Sociobiology, 62 (4), 479-497 DOI: 10.1007/s00265-007-0428-9