Fungal Partnership Boosts Digestion Speed in Carnivorous Plants

Insects have plenty to beware when it comes to carnivorous plants. Add an acid-loving fungus to that list of dangers.

Sundew plants have tentacle-like leaves that curl around and entrap flies and other insects in a sticky secretion called mucilage (SN: 5/16/18). As stuck prey suffocate in mucilage or die from exhaustion, the plant produces enzymes that dissolve the bodies into nutrients later absorbed by the leaves.

But plant enzymes alone aren’t the whole story. A fungus called Acrodontium crateriforme has a helping hand in the digestive process, researchers report in the October Nature Microbiology. A. crateriforme produces additional digestive enzymes and makes the leaf’s environment more acidic, which helps both plant and fungal enzymes mixed into the mucilage work more efficiently.

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“Ultimately this creates a synergistic effect,” says Isheng Jason Tsai, an evolutionary biologist at Academia Sinica in Taipei, Taiwan. Prey decomposition speeds up and the plant gets more nutrients.

Previous studies hinted that bacteria living in the mucilage of other carnivorous plants including pitcher plants and bladderworts could aid in digestion.

Confirming that a specific microbe can support digestion “reshapes our understanding of plant carnivory,” Tsai says. “This opens up new avenues to explore other carnivorous plants and their potential microbial helpers.”

Tsai and colleagues went hunting for microbes growing on spoon-leaved sundews (Drosera spatulata) — a species found in temperate and tropical regions including Taiwan — and found a diverse assortment of both bacteria and fungi. A. crateriforme topped the list as the most abundant, making up roughly an average 40 percent of the microbial genetic material found in leaf mucilage.

The team then sprinkled powdered ants on plants to mimic prey capture. A crateriforme reduced digestion time by roughly one-fifth, the researchers found, a sign that the fungus helps break down prey. Sterile plants without microbes took an average of 92 hours to digest the powder compared with 73 hours for plants inoculated with the fungus.

What’s more, the fungus grows on other Drosera species found in the United Kingdom, as well as D. rotundifolia and purple pitcher plants (Sarracenia purpurea) from the United States. That A. crateriforme dwells on sundew plants across three continents suggests an ancient relationship between the two, Tsai says. Finding the fungus on other carnivorous plants as well hints that “the relationship is a more widespread evolutionary strategy in botanical carnivory” — a match made in insect-gobbling heaven.