A scanning electron micrograph of a Malassezia species. CDC/Janice Carr

Thursday, November 8th, 2007--

Itchy scalp? Unwanted flakes? A fungus is at least partly to blame, according to researchers. Dandruff is related to the presence of certain species of Malassezia—ubiquitous, hard-to-eradicate fungi that live on humans and other mammals. This week, researchers in the fungi-fighting business report in the Proceedings of the National Academy of Sciences that they have sequenced the genome of Malassezia globosa, in the hopes that its genetic material will reveal a chink in its armor.

Malassezia live on your scalp--whether or not you have dandruff—and dine on the oil that your scalp excretes, the researchers say. The fungi break down the oil, called sebum, into free fatty acids, which can irritate the scalp. Irritation prompts the scalp to try to repair itself through extra cell production, which leads to dandruff. The repair also stimulates more sebum secretion, which means more fungi food.

Researchers don't know why only some people get dandruff. "Everybody has got Malassezia and everybody has got sebum... but for some reason some people get dandruff and other people don't," says Tom Dawson, author on the study and a biologist at Proctor and Gamble Beauty Company. But it's clear that Malassezia play a role, Dawson says. He and his colleagues at Proctor and Gamble are looking for ways to rid the scalp of Malassezia, as a treatment for dandruff.

Despite Malassezia's ubiquity, "very little research has been done on them over the past few years because almost no one was able to cultivate [the fungi] in the laboratory," Dawson adds.

Part of the challenge to growing them is that Malassezia are finicky eaters. In the lab, researchers feed them olive oil—which closely resembles our scalp's sebum. "We went through dozens of different types and brands of olive oils to find out the one that they really like," Dawson says. He declined to share the brand that worked, but says that Malassezia prefer the expensive stuff—extra-virgin only.

The M. globosa genome revealed a few interesting facts according to Dawson. First, the fungus lacks the gene that produces lipids. M. globosa can't make fats itself which explains why it is dependent on our sebum, Dawson says.

Malassezia are closely related to a corn fungus called corn smut (Ustilago maydis). This study showed that they share genes implicated in corn smut mating. Previously researchers thought Malassezia propagated only through cell division, called unipolar budding. Dawson says this could mean that Malassezia are capable of sexual reproduction—"that's a huge surprise."

Another key finding--with implications for the fight against dandruff--is what the fungus uses to break down the sebum. The researchers found that M. globosa secretes several types of proteins—lipases and proteases—that can break up sebum into something the fungus can digest. Dawson says: "Inhibition of these lipases would probably be a good thing for starving out the bug. Inhibition of proteases would be a good way to kill the bug."

--Flora Lichtman

Sources

Thomas Dawson
Principal Scientist Beauty Technology Department Proctor and Gamble Beauty Company

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