Smelly, itchy feet are constant reminders that we share our bodies with fungi. But just how many and what kinds? A new genetic survey has uncovered an incredible diversity of fungi on the feet, with different communities in the heel, toenail, and space between the third and fourth toes. The bottom of the heel alone hosts 80 different types, and if cataloged by species, the tally would likely be an order of magnitude higher. Fungi in each of these communities were similar from one person to the next, except in a woman who had a persistent toenail infection: She had lots of other fungi not found on the other nine people, indicating that more kinds of fungi could take up residence in the feet if they had the opportunity. (The bacteria on her feet, in contrast, were very typical of feet.) Meanwhile the rest of the body—from the inside of the nose or ear to the fold between the hip and groin—hosted primarily Malassezia, a genus of fungus that includes dandruff-causing species, the researchers report online today in Nature. Different Malassezia species took up residence in different body parts. There they thrive alongside of bacteria, as seen in this picture of a hair shaft (yellow) sampled from a back (bacteria, pink; fungus, blue-green). Skin bacteria tend to cluster into communities based on whether the skin is moist, dry, or oily, but fungi prefer specific regions of the body, irrespective of moisture content, possibly because those regions have different temperatures. The chest and back are 34°C, but the feet can be as low as 30°C. Those cool toes seem to be the perfect environment for many fungi. The diversity of fungi on the body, the researchers say, speaks to the need for personalized medicine in which doctors characterize the particular fungal infection between treating it.
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