Leaf-cutter ants and their marvelous microbiomes

March 8, 2012 § 1 Comment

Earlier this week, I showed up for The Social Biology of Microbial Communities meeting at the National Academies. The Institute of Medicine’s Forum on Microbial Threats hosted this two-day event to discuss all the ways that microbes communicate and work together in all kinds of ecosystems. One of the ecosystems discussed was leaf-cutter ants. A talk by Cameron Currie from the University of Wisconsin-Madison about these ants gave me a newly found appreciation for insect microbiomes.

By now, we’ve come to appreciate that as humans, we have microbiomes, such as the ones in our guts and skin. Currie has shown that insects, too, benefit from microbes that cozily live inside them.

Leaf-cutter ants, natives of South and Central America, clip off leaves, flowers and grasses and scurry back to their nests, wielding the vegetation above their heads. The ants feed fungus farms in their nests with the vegetation. The fungi, in turn, are made into food for the ant queen and the larvae.

But the fungus farm that the ants loving care for and make food out of are susceptible to attacks by pathogens. An example of a pathogen is escovopsis.

Leaf-cutter ants were originally thought to be coated in a wax. But as Currie explained in his talk, this “wax” turned out to be colonies of actinobacteria. These bacteria produce antibiotics that fend off escovopsis. (It turns out we too benefit from actinobacteria because two-thirds of the antibiotics we use are made by Streptomyces, a kind of actinobacteria).

Because these bacteria are useful for the ants in keeping their fungus gardens alive with their antibiotic production, the ants have specialized crypts with exocrine glands in their bodies to house and support these bacteria. Currie and his colleagues have demonstrated the presence of these crypts by electron microscopy and other techniques.

Currie said that the relationship between actinobacteria (which, in the case of these ants, is pseudonocardnia)  and leaf-cutter ants is ancient, stretching to 50 million years and perhaps older. Leaf-cutter ants aren’t the only insects to have friendly bacteria live on them — wasps, honey bees and Southern pine beetles are other examples of insects that get a helping hand from bacteria.

In looking up Currie’s publications, I discovered that Currie’s group has also done genomic and proteomic analyses on the bacterial diversity within the fungal gardens themselves. In gardens harvested by field and lab-based leaf-cutter ants, Currie and his colleagues showed that the fungi coexist with bacteria that help fungi feed on the plant material hauled in by the ants.

As Currie pointed out at the end of his talk at the IOM event, understanding insect-bacterial relationships can help us find natural products against pathogens.

You can watch Currie collect ants on his recent Costa Rica trip here.


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