Bacteria aren’t always bad. In fact, they can be extremely helpful partners. According to research at Washington University School of Medicine in St. Louis, microbes found naturally in the mouse and human gut interact with intestinal cells, called Paneth cells, to promote the development of blood vessels in the intestinal lining. “This study provides insights into the mutually beneficial partnerships forged between mammals and their native microbes,” says the principal investigator. “These symbiotic relationships probably are most important in the gut, which contains the largest and most complex collection of bacteria.”