, Schell recently worked with scientists at the Nestlé Research Center in Lausanne, Switzerland, to unravel some of the genetic secrets of B. longum. This microbe typically colonizes the intestines of a newborn mammal, thrives during the breast-feeding period, and then subsides after weaning, when B. thetaiotaomicron and other bacteria take hold. Nestlé incorporates B. longum into some of its products, such as infant formulas and yogurts, to promote gastrointestinal health.
In the Oct. 29, 2002 Proceedings of the National Academy of Sciences, Schell and his colleagues unveiled the entire DNA sequence of B. longum and identified a large roster of genes for enzymes that break apart sugars and other edible substances. Some of these enzymes may degrade complex sugars found in breast milk, speculates Schell. Others, such as ones that apparently break down plant gums, may help the bacterium survive later in its host's life when B. longum is in the minority in the intestines.
The bacterium appears to break down substances that B. thetaiotaomicron and other Bacteriodes can't handle. "It seems to be more specialized for the leftovers of metabolism," says Schell. In a strategy similar to Gordon's, investigators at Nestlé are now using germfree mice to evaluate B. longum's impact on intestinal genes.
Gordon's team is drawing its own insights from the group's recent deciphering of B. thetaiotaomicron's genome. Among that microbe's nearly 4,800 genes, several hundred encode proteins that bind carbohydrates, enzymes that degrade bonds between sugars, or enzymes that create new sugars, the investigators reported in the March 28 Science. And the activity of many of these genes appears to be regulated by genes encoding molecules related to known environmental sensors, suggesting that the microbe can monitor the contents of the intestines and quickly deploy the molecular machinery needed for it to digest nutrients.
"This organism has a sweet tooth. It knows how to process carbohydrates," says Gordon.
Over the next 5 to 10 years, predicts Schell, researchers will decode the genomes of many more intestinal microbes. Investigators may also begin to address such issues as whether a person's diet changes his or her intestinal microflora. "I think the gut population of a vegetarian is clearly going to be different" from that of a meat eater, says Schell.
Gordon offers an even more provocative question: Do intestinal microbes influence a person's weight? "Over time, could relatively minor differences in the ability to extract nutrients in some individuals predispose them to obesity?" he asks.
The complicated nation of bacteria within our intestines is a "window into our biology and how we've evolved as a species," concludes Gordon.
Heather is the Administrator of the IBS Message Boards. She’s the author of Eating for IBS and The First Year: IBS, and the CEO of Heather's Tummy Care. Join her IBS Newsletter. Meet Heather on Facebook!