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

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

Bio-based fuels, detergents, nutritional supplements, and even plastics are the result of this work. And while scientists have found ways to break down plants to the extent necessary to produce a range of products, some polymers, such as lignin, which is a primary ingredient in plant cell walls, remain incredibly difficult to break down. an affordable price without adding pollutants. the environment. These polymers can be discarded as waste products without further use.

A specialized microbial community composed of fungi, leaf 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 identify all the components and biochemical reaction required for the process has been a significant challenge – until now.

Kristin Burnum-Johnson, scientific group leader for Functional and Systems Biology at the Pacific Northwest National Laboratory (PNNL), and a team of PNNL research partners have developed an imaging method called metabolome informed proteome imaging (MIPI). . This method allows scientists to look at the molecular level and see exactly which basic components are part of the plant’s degradation process, as well as what, when and where important biochemical reactions occur that make it possible.

Using this method, the team revealed important metabolites and enzymes that stimulate various biochemical reactions that are vital in the degradation process. They also revealed the purpose of the bacteria residing in the system – which is to make the process even more efficient. These insights can be applied to the future development of biofuels and bioproducts.

The team’s research has been recently published in Chemical biology of nature.

Symbiotic relationship between leaf ants and fungi reveals key to success in plant degradation

For their research, the team studied a type of fungus known for its symbiotic relationship with a kind of leaf cutter ants– a fungus known as Leucoagaricus gongylophorus. The ants use the fungus to grow a fungus garden that degrades plant polymers and other material. The remaining components from this degradation process are used and consumed by a variety of organisms in the garden, allowing them all to thrive.

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

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

But what makes this fungal community so difficult to study is its complexity. While plants, fungi, ants and bacteria are all active components in the process of plant degradation, none of them focus on one task or reside in one place. Factor in the small-scale size of the biochemical reactions that occur at the molecular level, and an incredibly difficult puzzle presents itself. But the new MIPI imaging method developed at PNNL allows scientists to see exactly what happens 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,” said Burnum-Johnson.

Revealing important components in a complex system

Using a high-powered laser, the team took scans of 12-micron-thick sections of a fungal garden—the approximate width of plastic wrap. This process helped to determine the locations of metabolites in the samples, which are residual products of plant degradation. This technique also helped to identify 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 indicate hot spots where plant matter has been broken down.

From there, the team located in these regions to see the enzymes, which are used to kickstart biochemical reactions in a living system. Knowing the type and location of these enzymes allowed him to determine which microbes were part of that process.

All these components together help to affirm the fungus as the primary degrader of plant material in the system. In addition, the team determined that the bacteria present in the system transform previously digested plant polymers into metabolites that are used as vitamins and amino acids in the system. These vitamins are amino acids it benefits the entire ecosystem by accelerating the growth of fungi and the degradation of plants.

Burnum-Johnson said that if scientists used other, more traditional methods that take quantitative measurements of primary components in a system, such as metabolites, enzymes and other molecules, they would only get an average of those materials, creating more noise and masking. of the information.

“It dilutes the important chemical reactions of interest, often making these processes undetectable,” he said. “To analyze the complex environmental ecosystem of these fungal communities, we need to know those interactions in detail. These conclusions can be found in a laboratory setting and used to create biofuels and bioproducts that are important in our daily lives “.

Using knowledge of complex systems for future fungal research

Marija Velickovic, chemist and lead author of the paper, said she was initially interested in studying the fungal garden and how lignin degrades based on the difficulty of the project.

“Fungal gardens are the most interesting because they are one of the most complex ecosystems composed of many members working effectively,” he said. “I really wanted to map the activities at the microscale level to better understand the role of each member in this complex ecosystem.”

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

Velickovic and Burnum-Johnson said they are excited about their team’s success.

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

The team plans to use their findings for further research, with specific plans to study how fungal communities respond and protect themselves amid disturbances and other disturbances.

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