BOSTON—Add a new set of actors to the throng of gut microbes that influence health: fungi. So far, genetic sequencing of the microbiome has largely focused on bacteria, Brett Finlay, a microbiologist at the University of British Columbia in Vancouver, Canada, explained in a session here at the annual meeting of AAAS, which publishes Science. In 2015, Finlay and colleagues identified four bacteria that seemed to protect Canadian kids from developing asthma. They suspected that these bugs shaped the nascent immune system by bumping up levels of immune-modulating cells in the gut. But when the group sequenced the gut microbiome in a group of 100 children in Esmeraldas, Ecuador—a more rural setting, but with rates of asthma comparable to Canada’s—the best microbial predictor of asthma wasn’t a bacterium at all, but a genus of yeast known as Pichia (above). Three-month-olds who had it in their feces were more likely to develop asthma by the age of 5. How the yeast might boost asthma risk is far from clear—and it likely interacts with bacterial species to influence the immune system, Finlay says. But the find is new evidence that fungal organisms are not to be ignored. “The technology is there. We can do this now,” Finlay says. “And I think it’s going to open up another layer of complexity.”
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*Correction, 20 Februrary, 3:05 p.m.: A previous version of this story incorrectly stated that fungi were more abundant in the human microbiome than bacteria.