New imaging method unveils secrets of natural plant degradation process

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 degrade plants to the extent needed to produce a range of products, certain polymers such as lignin, which is a primary ingredient in the cell wall of plants, remain incredibly difficult to affordably break down without adding pollutants back into the environment. These polymers can be left behind as waste products with no further use.

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

Kristin Burnum-Johnson, science group leader for Functional and Systems Biology at Pacific Northwest National Laboratory (PNNL), and a team of fellow PNNL researchers have developed an imaging method called metabolome informed proteome imaging (MIPI). This method allows scientists to peer deep down to the molecular level and view exactly which base components are part of the plant 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 spur different biochemical reactions that are vital in the degradation process. They also revealed the purpose of resident bacteria in the system—which is to make the process even more efficient. These insights can be applied to future biofuels and bioproducts development.

The team’s research was recently published in Nature Chemical Biology.

Kristin Burnum-Johnson, PNNL science group leader for Functional and Systems Biology, talks about her research studying the molecular intricacies of how leafcutter ants work with a type of fungus to degrade hard-to-break-down plant material as part of a TEDx Talk in Richland, Wash. Credit: TEDx Talks

Symbiotic relationship between leafcutter ants and fungus reveal key to success in plant degradation

For its research, the team studied a type of fungus known for its symbiotic relationship with a species of leafcutter ants—a fungus known as Leucoagaricus gongylophorus. The ants use the fungus to cultivate a fungal garden that degrades plant polymers and other material. Remnant components from this degradation process are used and consumed by a variety of organisms in the garden, allowing all to thrive.

The 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 help with the 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 better learn 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. While the plants, fungus, ants, and bacteria are all active components in the plant degradation process, none of them focus on one task or reside in one location. Factor in the small-scale size of the biochemical reactions occurring 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 is going on 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.

Source: Pacific Northwest National Laboratory

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