Scientists have sequenced the genome of one of the most important residents in the human gastrointestinal tract, a bacterium that keeps the digestive system running smoothly, blocks the growth of harmful bacteria, and boosts the immune system. The microbe, called Bifidobacterium longum, is often the dominant bacterium found in humans. The researchers identified a number of proteins specialized to help B. longum interact with the human host and persist against harmful bacteria. They can now closely look at which genes allow B. longum to live in different environments such as dairy products, vegetables and the human gastrointestinal tract. Bacteria such as B. longum ferment sugars into lactic acid and have many health benefits. For these reasons, researchers of the food and drug industry have taken a keen interest in using these organisms. Bifidobacterium longum is among the first colonizers of the sterile digestive tract of newborns and predominate in breast-fed infants, according to the scientists. The research team isolated the bacterium from the feces of an infant. Fabrizio Arigoni, of the Swiss food and infant formula manufacturer NestlÃ© in Lausanne, led the study. Formula-fed infants have a different microflora, and this may be related to the higher risk of diarrhea and allergies in these babies. "This progressive colonization is thought to be important for development of immune system toleranceâ€¦lack of such tolerance possibly leads to food allergies and chronic inflammation," the researchers write in Proceedings of the National Academy of Sciences.