Fungus-Chomping Micro Predators Could Protect Amphibians from Deadly Skin Disease

Microbes that thrive in lakes happily consume the pandemic fungus that has caused declines in more than half the planet’s amphibian species

In 2012 a team of temperamental donkeys picked their way down the French Pyrenees carrying a payload of voracious protists. Donkeys wouldn’t ordinarily be required to ferry single-celled microbes, but these tiny organisms happened to be inhabitants of the several hundred pounds of lake water that the donkeys were also carrying, whether they liked it or not. “It’s kind of funny,” says Dirk Schmeller, the scientist whose team hired the donkeys, “because it shows donkeys can help save amphibians.”
 
What makes that unlikely scenario possible is the microorganisms’ appetite for an equally minute chytrid fungus—a group of fungi with a swimming stage that resemble the ancestors of all fungi—called Batrachochytrium dendrobatidis, or Bd, which is wiping out amphibians worldwide. It turns out that a diverse collection of single-celled protists and tiny multicellular animals naturally hunt down and eat Bd in lakes, preventing the killer fungus from infecting frogs and other amphibians. Although Bd is an introduced fungus, similar fungi are abundant in lakes and a natural part of these micro predators’ diets, so their ability to prey on Bd is not unexpected. What was unexpected was the gusto with which they can eat the invasive fungus in the wild. Scientists had previously shown in experimental lab containers that a few micro predators would eat swimming Bd spores, but a new study indicates that the hunt happens in real-world mountain lakes, and seems to be taking place on a scale large enough to significantly reduce amphibian infections and deaths in those lakes. Schmeller, of the Helmholtz Center for Environmental Research in Germany, and colleagues published these conclusions in January in Current Biology.
 
The promising implication is that capitalizing on native microorganisms’ Bd-feasting ability could cut down the pandemic fungus enough to boost amphibian survival, without relying on the iffy introduction of foreign bacteria or deployment of ecosystem-disrupting antifungal chemicals—two methods that have been proposed. Rather, protecting amphibians may be as simple as promoting the health and survival of the microbes that already live in a lake or introducing them where they’ve been lost or suppressed.

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