SUMMARY: Leaf-cutter ants and a fungus called Leucoagaricus gongylophorus have a symbiotic relationship. The ants harvest plant material for the fungus to “eat” and then the ants feed off of the gongylidia. These swollen parts of the hyphae are no longer found anywhere else in the world, as the fungus produces these solely for the ants. Scientists looked at what enzymes were produced when leaf-cutter ants were given different types of plant substrates to cultivate their fungal gardens. Researchers wanted to know if the fungus was, in a sense, digesting the plant material for the ants (like a giant, exterior digestive system) or if something else was going on.
Results showed that the fungus modified the types of enzymes produced based on the plant materials available to them. Leaves and flowers caused an increase in cellulose-digesting enzymes. Oats and mixed-litter (of leaves, flowers, and oats) caused an increase in a different set of enzymes, ones that digested things like starch (easy-to-break-down carbohydrates). Scientists believe that this happens because the fungi will “eat” the easily-accessible carbohydrates first before expending the energy to break down tougher carbohydrates (such as cellulose).
LESSON COMMENTS: If you’re teaching a class on the isomeric differences between cellulose and starch, enzyme specificity, mutualism, or rainforest biodiversity, this article is a great supplement. The Abstract and Discussion sections are easy to read and for younger students or students at lower reading levels, the graphs and diagrams of the various fungal enzymes are clear and easy to understand. Some activities teachers can do with students include comparing/contrasting this mutualistic relationship with the digestive system or having students explore research articles on the gut microbiome. There’s one part of the paper (4th paragraph of the Discussion section) where the researchers describe the ants defecating on the top of the leaf litter pile as an enzymatic pretreatment for decomposition. Teachers can ask students to draw analogies to human digestion and perhaps even food processing (the example that comes to mind is using coffee beans that have been through the digestive tract of a civet cat).
Khadempour, L., Burnum-Johnson, K. E., Baker, E. S., Nicora, C. D., Webb-Robertson, B. M., White, R. A., 3rd, … Currie, C. R. (2016). The fungal cultivar of leaf-cutter ants produces specific enzymes in response to different plant substrates. Molecular ecology, 25(22), 5795–5805. doi:10.1111/mec.13872
