Sloth Hair Harbors Medicinal Fungi

The three-toed sloth, a tree-dwelling mammal from the rainforests of Central and South America.  Photo by Stefan Laube
The three-toed sloth, a tree-dwelling mammal from the rainforests of Central and South America. Photo by Stefan Laube

by Kate Wheeling
BU News Service

Sloths are known for their slow-paced lifestyles. Their sedentary habits allow sloths to pick up a wide variety of microscopic passengers that settle down in the cracks that crisscross their coarse, spongy hair.

A vast fungal community thrives in this shaggy, green-algae glazed coat, churning out bioactive compounds that could one day serve as the basis for new drugs, according to a new study published January 15th in PLoS ONE. The study’s authors identified over 80 distinct fungal species from sloth hair samples, many of which proved to have anti-parasitic, anti-bacterial and even anti-cancer activity.

“The structure of sloth hair itself is ideal,” says Higginbotham. The crazed hairs absorb water like a sponge, creating a warm damp environment where myriad microorganisms cohabitate in a fast-paced community that drives up competition for space and thus the production of bioactive compounds.

“It’s a pretty clever study,” says Nicholas Oberlies, professor of chemistry and biochemistry at the University of North Carolina at Greensboro. It’s a new niche for scientists to explore in their search for new bioactive compounds.

The researchers took hair samples from nine living three-toed sloths living in Soberanía National Park, Panama in February 2011. Higginbotham and her colleagues at the Smithsonian Tropical Research Institute, UC Santa Cruz, and the University of Arizona, chopped up the hair samples, placed them on agar plates and collected anything that would grow—an important step in drug development research; if it doesn’t grow in the lab, it can’t be used to make drugs. They identified 84 fungal species, three of which were previously unidentified.

The authors used concentrated samples of the fungi, to test for bioactivity against parasitic diseases, cancer cells, and pathogenic bacteria. The crude fungal extracts were considered highly bioactive if they inhibited 50% of the growth of the pathogens and cancer cells they were tested against. They found two fungi that were highly bioactive against the malaria parasite, eight active against the parasite that causes Chagas disease, and a full 15 fungal species that produced compounds active against the breast cancer cell line MCF-7. Another 20 fungi had antibacterial properties. At least one killed off Gram-negative bacteria in a way that didn’t match up with any known antibiotics, suggesting a completely new mode of action—a valuable attribute for potential drugs.

This is just the first step towards the identification of bioactive compounds suitable for drug development. Future studies will need to look at purer, more concentrated samples of the bioactive fungi identified, rule out anything with less than 90% inhibition rates, and tweak growing conditions in the lab so that they’re closer to nature. In the lab, under ideal conditions, fungi might quit producing the same bioactive compounds they need to compete out in the wild.

“It’s quite likely that what they produce in the lab is only a snapshot of what they produce in the wild,” says Higginbotham.

Higginbotham and her co-authors demonstrate that there are still plenty of places to look for new antimicrobials, but in order to tap into those resources we have to preserve them. Some species of sloth, like the pygmy three-toed sloth, are critically endangered. Studies like this demonstrate why “it’s more valuable to have that rainforest as a rainforest than it is to turn it into some sort of turpentine plantation,” says Oberlies. “The conservation aspect transcends the science.”