Writing in the March 18 issue of Science, the researchers report that the yeast Candida glabrata use a family of proteins called sirtuins to block access to genes that would otherwise help the yeast stick. The sirtuins, which also help regulate the organism's lifespan, require niacin, or vitamin B3, to work. But urine has only tiny amounts of niacin, so the sirtuins don't work, the genes are exposed, and the yeast can make the proteins that help it stick to cells in the urinary tract, the researchers discovered.
C. glabrata and its cousin C. albicans cause infections in blood and in mucosal tissues such as the urinary tract and vagina. C. glabrata is the second leading cause (behind C. albicans) of yeast infections, or candidiasis, in people with urinary catheters. Unlike some other yeast, C. glabrata can't make niacin and instead has to import it from its surroundings.
"This particular yeast has in some sense committed to living with the human host and so it takes advantage of us to provide certain key nutrients," says Brendan Cormack, Ph.D., professor of molecular biology and genetics in Johns Hopkins' Institute for Basic Biomedical Sciences.
"It turns out that there's enough niacin in blood to keep the yeast's adhesion-promoting genes turned off, we discovered," he adds. "But in urine and perhaps other host environments, there is such a limited amount of niacin that these genes are turned on, allowing the organism to stick to host cells."
The new study builds on the lab's discovery in 1999 that C. glabrata sticks to cells that line mucosal tissue
Contact: Joanna Downer
Johns Hopkins Medical Institutions