It is about the microscopic bugs that live all over your body – on your skin, in your mouth, in your nose, and in particular your digestive tract. These bugs are so numerous that they outnumber your own cells by a factor of 10. You are vastly more microbe than human.
Before you get so disgusted you stop reading, consider this: many of these bugs are as essential to your life as your own cells. These microbes have been around since before humans existed, and our bodies have evolved to adapt to their presence just as they have adapted to ours.
They are also – to quote one expert – the “last frontier” of medical research, a crucial aspect of our health that scientists rarely considered until recently. It is also one of the most daunting challenges facing biologists today.
“We know next to nothing about this whole universe that we host,” according to Bruce Birren, co-director of the Genome Sequencing and Analysis Program at the Broad Institute, a research collaborative between Harvard and MIT scientists. “It’s as if we’re coming to a planet for the first time and asking: what do we find?”
What experts like Birren are discovering is the powerful role these tiny bugs might be playing in our lives. The 1,000-or-so species of microbes that live in our guts control digestion, and possibly so much more. They are strongly linked with the rise in allergies and asthma, and with digestive problems like Crohn’s disease and colitis. They also influence the immune system, and there is a growing body of evidence suggesting that gut microbes could have an influence on cancer risk. They could also dictate whether we are packing on extra pounds or liable to get diabetes.
And that is not all. Recent studies have shown that germ-free mice are much more vulnerable to stress. Two strains of mice known for their distinct personalities – one warm and friendly, the other aggressive and standoffish – swapped traits when given each other’s gut microbes. Other studies have altered rats’ response to heart attacks by changing the gut microbes they were fed before the attack. And a group of mice fed a high-protein diet had different gut microbes and better memory skills than mice fed a typical diet.
“We can’t really understand human health without understanding how we interact with all these microbes,” says Birren.
This year sees the culmination of two major projects seeking to better understand the full repertoire of bugs that colonize us – what scientists call the microbiome. In 2007, the United States government launched a five-year, $157 million Human Microbiome Project, aimed at sequencing the genomes of microbial populations living in the mouths, guts, armpits and other orifices of 300 healthy Americans.
The following year the European Commission launched a $29 million project called Metagenomics of the Human Intestinal Tract, or MetaHIT, which focuses on gut bacteria only. Initial findings from both efforts were presented at the International Human Microbiome Congress in Paris last month. “Both have made absolutely tremendous progress,” says Dusko Ehrlich, coordinator of MetaHIT and research director at the National Institute for Agricultural Research in France.
While some researchers are wary of overhyping any results, Ehrlich says he and other scientists are confident in the potential of the human microbiome research – even more so than they were a decade ago when all the talk was about the human genome. “It’s hard to be a prophet,” Ehrlich says, “but we see so much more potential in the human-other-genome than in our own genome.”