How leafcutter ants cultivate a fungal garden to degrade plants could provide insight into future biofuels

Scientists have spent decades finding ways to degrade plant materials efficiently and affordably so that they can be converted into useful bioproducts that benefit everyday life.

Biofuels, detergents, nutritional supplements and even plastics are the result of this work. And while scientists have found ways to degrade plants to the extent necessary to produce a range of products, some polymers such as lignin, which is a main ingredient in plant cell walls, remain incredibly difficult to break down at low cost. cost without reintroducing pollutants into the environment. the environment. These polymers can be left as waste without further use.

A specialized microbial community composed of fungi, leaf-cutter ants, and bacteria is known to naturally degrade plants, transforming them into nutrients and other components that are absorbed and used by surrounding organisms and systems. But identifying all the components and biochemical reactions necessary for the process has remained a significant challenge until now.

Kristin Burnum-Johnson, scientific group leader for functional and systems biology at Pacific Northwest National Laboratory (PNNL), and a team of fellow PNNL researchers developed an imaging method called metabolome-informed proteome imaging (MIPI). . This method allows scientists to look in depth at the molecular level and see exactly which basic components are part of the plant breakdown process, as well as what, when and where the important biochemical reactions that make this possible occur.

Using this method, the team revealed important metabolites and enzymes that trigger different biochemical reactions essential to the degradation process. They also revealed the purpose of the resident bacteria in the system: to make the process even more efficient. This knowledge can be applied to the future development of biofuels and bioproducts.

The team’s research was recently published in Natural chemical biology.

Symbiotic relationship between leaf-cutter ants and fungi reveals key to successful plant degradation

For their research, the team studied a type of fungus known for its symbiotic relationship with a species of leaf-cutter ants, a fungus known as Leucoagaricus gongylophorus. Ants use the fungus to cultivate a fungal garden that degrades plant polymers and other materials. The remaining components of this degradation process are used and consumed by various garden organisms, allowing all to thrive.

Ants accomplish this process by growing fungi on fresh leaves in specialized underground structures. These structures ultimately become fungal gardens that consume the material. Resident bacterial members contribute to degradation by producing amino acids and vitamins that support the overall garden ecosystem.

“Environmental systems have evolved over millions of years to become perfect symbiotic systems,” Burnum-Johnson said. “How can we learn better from these systems than by observing how they accomplish these tasks naturally?”

But what makes this fungal community so difficult to study is its complexity. Although plants, fungi, ants, and bacteria are all active components in the plant decay process, none of them focus on a single task or reside in a single location. If we take into account the small size of biochemical reactions occurring at the molecular level, an incredibly difficult puzzle presents itself. But the new MIPI imaging method developed at PNNL allows scientists to see exactly what’s happening throughout the degradation process.

“We now have the tools to fully understand the intricacies of these systems and visualize them as a whole for the first time,” Burnum-Johnson said.

Reveal important components of a complex system

Using a high-power laser, the team scanned 12-micron-thick sections of a fungal garden, the approximate width of plastic wrap. This process made it possible to determine the location of metabolites in the samples, which are residual products of plant degradation. This technique also identified the location and abundance of plant polymers such as cellulose, xylan and lignin, as well as other molecules in specific regions. The combined locations of these components indicated hotspots where plant material had been degraded.

From there, the team focused on these regions to observe the enzymes used to trigger biochemical reactions in a living system. Knowing the type and location of these enzymes allowed them to determine which microbes were part of this process.

All of these components together have helped establish the fungus as the primary degrader of plant material in the system. Additionally, the team determined that bacteria in the system transformed previously digested plant polymers into metabolites used as vitamins and amino acids in the system. These vitamins and amino acids benefit the entire ecosystem by accelerating fungal growth and plant breakdown.

Burnum-Johnson said that if scientists had used other, more traditional methods that take aggregate measurements of the primary components of a system, such as metabolites, enzymes and other molecules, they would simply obtain an average of these materials, thus creating more noise and hiding information.

“This dilutes important chemical reactions, often making these processes undetectable,” she said. “To analyze the complex environmental ecosystems of these fungal communities, we need to know these detailed interactions. These findings can then be taken back to the laboratory and used to create biofuels and bioproducts important in our daily lives.”

Using knowledge of complex systems for future fungal research

Marija Velickovic, a chemist and lead author of the paper, said she initially became interested in studying the fungal garden and how it degrades lignin because of the difficulty of the project.

“Fungal gardens are most interesting because they are one of the most complex ecosystems, made up of multiple members that work effectively together,” she said. “I really wanted to map activities on a microscopic scale to better understand the role of each member in this complex ecosystem.”

Velickovic performed all the hands-on laboratory experiments, collecting material for the slides, scanning the samples to visualize and identify metabolites in each of the sections, and identifying lignocellulose degradation hotspots.

Velickovic and Burnum-Johnson said they were delighted with their team’s success.

“We actually accomplished what we set out to do,” Burnum-Johnson said. “Especially in science, it’s not guaranteed.”

The team plans to use its findings for further research, with specific plans to study how fungal communities respond and protect themselves in the face of disturbances and other disturbances.

“We now understand how these natural systems degrade plant material very well,” Burnum-Johnson said. “By looking at complex environmental systems at this level, we can understand how they carry out this activity and leverage it to make biofuels and bioproducts.”