Yeast missing sex genes undergo unexpected sexual re...( DURHAM N.C. An emerging form of the ...)

DURHAM, N.C. An emerging form of the pathogenic yeast Candida is able to complete a full sexual cycle in a test tube, even though it's missing the genes for reproduction. And it may also do so while infecting us, according to Duke University Medical Center researchers.

"Sex contributes to the Candida yeast species' evolutionary success," said Joseph Heitman, M.D., Ph.D., director of the Center for Microbial Pathogenesis in the Duke Department of Molecular Genetics and Microbiology and co-author of two papers that tell the story in Nature and Current Biology. "I think the fact that it has a complete sex cycle is likely to play a role in the evolution of drug resistance in this emerging pathogenic yeast species. "

Yeast infections are notoriously hard to treat and yeast are one of the most successful pathogens and commensals in nature, he said. A commensal is an organism that benefits from associating with another organism without affecting the other. Humans are susceptible to three types of yeast infection: thrush (in the mouth and throat), vaginal infection, and a sometimes fatal systemic infection of bloodstream and organs, such as the kidney.

In a paper published online May 24 in Nature, Heitman's team reports that eight Candida species which have a sexual cycle were missing many of the genes related to reproduction found in other species.

"The unrecognized sex cycle could mean we need to develop new treatments to combat what is really happening in humans infected by yeast," said co-author Jennifer Reedy M.D. Ph.D.

With co-author Anna Floyd, Heitman and Reedy explored the question further in a study appearing in the May 14 Current Biology. The major question was: how could the yeast sexually produce spores when they lack so many genes responsible for meiosis, the process of sexual cell division that reduces chromosomes to half their number in the progeny?
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