Pathogenic fungus craves your brain sugar


This photomicrograph depicts Cryptococcus neoformans using a light India ink staining preparation. Life-threatening infections caused by the pathogen have been increasing steadily over the past 10 years because of the onset of AIDS and the expanded use of immunosuppressive drugs. Cryptococcus fungi thrive on a sugar called inositol, which is abundant in the human brain and spinal cord. (Courtesy: Centers for Disease Control/Wikimedia Commons)

DUKE (US)—Highly dangerous Cryptococcus fungi love sugar and will consume it anywhere because it helps them reproduce. In particular, they thrive on a sugar called inositol, which is abundant in the human brain and spinal cord.

To borrow inositol from a person’s brain, the fungi have an expanded set of genes that encode for sugar transporter molecules. While a typical fungus has just two such genes, Cryptococcus have almost a dozen, according to Joseph Heitman of Duke University.

“Inositol is abundant in the human brain and in the fluid that bathes it (cerebral spinal fluid), which may be why this fungus has a predilection to infect the brain and cause meningitis,” Heitman says, chair of Duke’s Department of Molecular Genetics and Microbiology. “It has the machinery to efficiently move sugar molecules inside of its cells and thrive.”

The findings on Cryptococcus genes were published online in the inaugural issue of mBio, a new open access microbiology journal.

This specialized brain attack likely occurred because these fungi adapted to grow on plants in the wild, which also are abundant in inositol, says lead author Chaoyang Xue, formerly a postdoctoral research associate in the Heitman lab and now an assistant professor at the Public Health Research Institute at the University of Medicine and Dentistry, New Jersey. “In fact, this pathogenic yeast has more inositol transporters than all other fungi we have compared it to in the fungal kingdom, based on what we know from genome research.”

The team of researchers discovered that inositol stimulates Cryptococcus to sexually reproduce. “A connection between the high concentration of free inositol and fungal infection in the human brain is suggested by our studies,” Xue says. “Establishing such a connection could open up a new way to control this deadly fungus.”

Cryptococcus’ love for sugar may also be a fungal Achilles Heel, Heitman notes.

“Now scientists may be able to target the fungi by developing ways to put them on the fungal equivalent of an Atkin’s low-carbohydrate diet so they will stop multiplying.”

He says researchers could use the new findings to devise different types of strategies to block Cryptococcus infections.

Researchers from the University of British Columbia and University of South Florida also contributed to the work, which received support from the National Institute of Health/National Institute of Allergy and Infectious Diseases grants.

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