Inside the human body, another ecosystem exists. The gut microbiome is home to trillions of species that work to regulate the immune response, fertility, and emotional health in exchange for food and shelter. But how this symbiotic relationship with this specific group of microbes came about remained poorly understood until now.
“There is a huge amount of variation in microbiome composition between individuals,” William Ludington, senior study author explains in a statement. “For example, if you look at the sum total of all of the bacterial species that are adapted to live in the gastrointestinal systems of humans, most of these are not present in a majority of people. That’s how incredibly diverse these gut microbial populations are.”
While some researchers have looked at the microbiome composition in natural populations, there have not been many attempts to use a controlled environment to pinpoint when new species decide to take part in the gut ecosystem.
Dr. Ludington and his team developed a new ecological model looking at the microbiomes of fruit flies — immensely less complicated than the human microbiome — and found that exposure to a microbial species does not mean it’s guaranteed entry to the microbiome ecosystem.
“Even among genetically identical flies that lived in the same housing and were fed the same diets, we saw variations in microbiome composition,” notes co-author David Sivak, from Simon Fraser University.
Instead, the general state of the microbiome, and how existing species in the microbiome interact with each other determine whether a newly encountered bacteria is allowed to join. “Think of microbiome composition as a big party where the social dynamics determine who leaves early and who stays until dawn,” says Dr. Ludington.
Researchers used mathematical models to simulate scenarios in which new microbiome species would be added to mix, emphasizing the importance of community factors that determine the odds of entering the microbiome ecosystem.
“The beauty of the mathematical approach we deployed is that it acknowledges that colonization is a roll of the dice, but we are now able to attribute the weighting of the dice to biological interactions with a molecular basis that has been honed by evolution,” says co-author Jean Carlson, from the University of California at Santa Barbara.
The study is available in the journal Proceedings of the National Academy of Sciences.