San Diego, Calif., March 6, 2018—In a new, collaborative study, researchers at the University of California San Diego Center for Microbiome Innovation (CMI) and colleagues across the nation have discovered the mechanism by which a canopy-dwelling herbivorous ant acquires the nitrogen it needs to synthesize essential amino acids: by way of the urine-eating bacteria that took up residence in its gut 46 million years ago. The findings are published in the March 6 issue of Nature Communications, and provide insight into agricultural insect management.
Nitrogen is a key component of living cells, and a major constituent of the nucleic acids and proteins directing their structure and function. Animals that eat plants face the challenge of obtaining enough of the usable form of nitrogen, since it is lacking in their preferred foods.
Canopy-dwelling ants fall into that category; typically viewed as predators or omnivores, several ants, like the turtle ant, are functional herbivores. They feed on nectar, pollen, fungi, vertebrate waste and plant wound secretions. Nitrogen, in its usable form, is limited in such foods. Turtle ants have also been observed consuming mammalian urine and bird feces, which contain large quantities of waste nitrogen only accessible with the aid of microbes.
Recently, researchers found that herbivorous ants that live in the canopy have three to four orders of magnitude more bacteria in their gut than ground-dwelling ants. Why do canopy-dwelling ants need so many bacteria in their guts, if not for nitrogen acquisition?
|PC: Jon Sanders|
Now, researchers have discovered that some of these gut bacteria have genes that enable them to recycle urea, and likely uric acid—together, urine. The ant then acquires in substantial quantities the recycled nitrogen and uses it to synthesize essential amino acids.
Furthermore, the researchers noticed that when given antibiotics, the ants were unable to acquire nitrogen in its usable form in experiments where urea was the only form of nutrition.
Turtle ants aren’t the only insects with nitrogen-provisioning symbionts in their guts—wood-feeding termites get up to 60 percent of their nitrogen from their symbionts, as do leaf-cutter ants from their fungus gardens.
“We don’t know the exact breakdown in nature, but it’s clear that the canopy-dwelling ants are getting enough nitrogen from eating small quantities of the vertebrate urine and fecal matter they come across in the trees—and from their own waste—to enable them to eat mostly plants,” said Jon Sanders, co-lead author on the paper. Sanders conducted the majority of his research under Naomi Pierce, Hessel Professor of Biology in the Deptartment of Organismic and Evolutionary Biology at Harvard, and Curator of Lepidoptera at the Museum of Comparative Zoology. He is now a postdoctoral fellow in CMI faculty director Rob Knight’s lab at UC San Diego.
But for Sanders, it’s not the transaction that’s the most exciting, it’s the relationship; the ants and bacteria appear to be in a very long-term relationship—46 million years!
We tend to think of microbial evolution as a quick and relatively unstable process, said Sanders. When we do experiments in a petri dish, we often end up working with only one strain because we can’t get multiple strains to coexist peacefully; they’re all fighting for nutrients. So how the heck did something like this happen?
That’s what Sanders will be looking into in the future. If we can understand how to get bacteria to coexist, we might be able to engineer more complex biological production lines, taking advantage of the capabilities of multiple types of microbes.
Implications for agriculture
The multimillion-year-long stability of the ant gut microbiome stands in stark contrast to what has been observed in humans—namely, that the composition of the gut microbiota changes depending on several factors, including the environment and diet of the host.
“For example, there’s a study that found that some Japanese people harbor enzymes in their intestinal bacteria that help them digest seaweed, and these are enzymes that North Americans lack,” said Sanders. “We are learning that what it means to have a microbiome is categorically different among animals.”
The lesson is two-fold: firstly, not all microbiomes were created equal, and as such, we need to be careful when comparing them. Secondly, a comprehensive understanding of these interactions in ants could provide insights into insect management in agriculture.
“What if we could give insects antibiotics to disrupt their microbiome and inhibit their ability to make use of plant material?” said Sanders.
Could agriculture benefit from manipulating the gut microbiomes of insects? Partner with the Center for Microbiome Innovation to find out!
About the Center for Microbiome Innovation
The objective of the Center for Microbiome Innovation (CMI) is to accelerate microbiome research and understanding, through partnerships with industry sponsors. By developing novel tools and methods through the analysis and manipulation of microbiomes—the distinct and diverse communities of bacteria, viruses and other microorganisms that live within and around us—we are taking what nature has been doing for centuries, and maximizing it to benefit the environment and reduce the cost of doing business. This is a multidisciplinary center with access to all the latest omics tools (genomics, metagenomics, metatranscriptomics, metabolomics, multiplex proteomics). We process hundreds of thousands of samples each year and analyzing and collecting data for some of the largest microbiome cohorts in the world.