Scientists have spent decades finding ways to efficiently and economically break down plant material into useful bioproducts that benefit everyday life.
Biofuels, detergents, food additives and even plastic are the result of this work. While scientists have found ways to break down plants to the extent necessary to produce various products, some polymers, such as lignin, a key component of plant cell walls, are notoriously difficult to break down cheaply without reintroducing contaminants. . Wednesday. These polymers can be left as waste without any use.
A specialized microbial community of fungi, leaf-cutter ants, and bacteria is known to naturally decompose plants and convert them into nutrients and other components that are absorbed and used by surrounding organisms and systems. However, identifying all the components and biochemical reactions required for this process still remains a major challenge.
As part of a Department of Energy (DOE) Early Career Award, Christine Burnum-Johnson, director of the Functional and Systems Biology Research Group at Pacific Northwest National Laboratory (PNNL), and a team of PNNL researchers have developed an imaging method. called metabolomics. Informed Proteome Imaging (MIPI). This technique allows scientists to get down to the molecular level and see what the building blocks of plant decomposition are, as well as what, when and where the important biochemical reactions that make it possible occur.
Using this method, the team discovered important metabolites and enzymes that control various key biochemical reactions during the decomposition process. They also discovered the purpose of the system's resident bacteria: to make the process more efficient. This knowledge can be applied to the future development of biofuels and bioproducts.
The team's research was recently published in the journal Nature Chemical Biology.
The symbiotic relationship between leafcutter ants and fungi is key to successful plant degradation.
For the study, the team studied a fungal species known for its symbiotic relationship with leafcutter ant species: a fungus known as Leucoagaricus gongylophorus. The ants use the fungus to grow a fungal garden that decomposes plant polymers and other materials. The residual components from this decomposition process are used and consumed by various garden organisms, allowing them to thrive.
The ants carry out this process by growing fungi on fresh leaves in special underground structures. These structures eventually become fungal gardens that consume the material. Resident bacteria promote decomposition, producing amino acids and vitamins that support the overall garden ecosystem.
“Environmental systems have evolved over millions of years into perfect symbiotic systems,” Burnum-Johnson said. “What better way to learn from these systems than to watch them perform these tasks naturally?”
But what makes studying this fungal community difficult is its complexity. Although plants, fungi, ants and bacteria are active components of the plant decomposition process, none of them are focused on a single task or coexist. Given the small-scale nature of biochemical reactions that occur at the molecular level, this poses an incredibly complex mystery. But a new MIPI imaging technique developed at PNNL allows scientists to see exactly what is happening during the decomposition process.
“We now have the tools to fully understand the complexities of these systems and visualize them in their entirety for the first time,” Burnum-Johnson said.
Identify important components in a complex system.
Using a powerful laser, the team scanned sections of the mushroom garden that were 12 microns thick, the width of a piece of plastic wrap. This process helped detect metabolites in the samples, which are remnants of plant decomposition. This method also helped determine the location and abundance of plant polymers such as cellulose, xylan, and lignin, as well as other molecules in some regions. The co-location of these components indicates hot spots where plant material is decomposing.
From there, the team traveled to these regions to study the enzymes used to initiate biochemical reactions in a living system. By knowing the type and location of these enzymes, they were able to determine which microbes were involved in this process.
All of these components together helped confirm that the fungus is the primary decomposer of plant material in the system. Furthermore, the team found that bacteria in the system convert previously digested plant polymers into metabolites that are used in the system as vitamins and amino acids. These vitamins and amino acids accelerate fungal growth and plant decay, benefiting the entire ecosystem.
Burnum-Johnson said that if scientists used other, more traditional methods to measure the masses of key components of a system, such as metabolites, enzymes and other molecules, they would simply be averaging those materials, which creates more noise and obscures information . .
“This dilutes the important chemical reactions of interest, making these processes often undetectable,” he said. “To analyze the complex ecological ecosystems of these fungal communities, we need to know these detailed interactions. These results can then be transferred to laboratory conditions and used to create biofuels and bioproducts that are important in our daily lives."
Use knowledge of complex systems for future fungal research.
Maria Velikovic, chemist and lead author of the paper, said that due to the complexity of the project, she was initially interested in learning about the fungus and how it destroys lignin.
“Mushroom gardens are very interesting because they are one of the most complex ecosystems with many members working together effectively,” he said. “I really wanted to map activities at the micro level to better understand each member's role in this complex ecosystem.”
Velikovic conducted all the hands-on experiments in the lab, collected material for slides, scanned the samples to see and identify metabolites in each compartment, and identified hot spots for lignocellulose degradation.
Both Velikovic and Burnum-Johnson said they were pleased with their team's success.
“We actually accomplished what we set out to do,” Burnum-Johnson said. “It's not guaranteed, especially in science.”
The team plans to use the findings for future research and specifically study how fungal communities respond to and defend against disturbances and other disturbances.
“We now have a very good understanding of how these natural systems break down plant matter,” Burnum-Johnson said. “By looking at complex ecosystems at this level, we can understand how they carry out these activities and how they use them to produce biofuels and biofuels.”
The work was funded by the U.S. Department of Energy's Office of Science. Additionally, the researchers had access to mass spectrometry imaging, computational and proteomic resources at the Environmental Molecular Sciences Laboratory, an Office of Science user facility located at PNNL.
