Plastic Degradation and Upcycling by the Gut Microbiome of Yellow Mealworms
Authors:
Ross Klauer1, Alex Hansen1*, Jenna Ott1, Lummy Maria Oliveira Monteiro1, Jyoti Singh1, Harrison Hall2, Nick Reichart3, Sankarganesh Krishnamoorthy3, Aaron Wright2, Mark Blenner1, Kevin Solomon1
Institutions:
1Chemical and Biomolecular Engineering, University of Delaware; 2Biology, Baylor University; 3Biological Sciences Division, Pacific Northwest National Laboratory
Goals
This project discovers and reconstructs the plastic degradation pathways distributed across the gut microbiome of yellow mealworms (larvae of Tenebrio molitor) to develop enhanced capabilities for biologically based polymer recycling.
Abstract
Globally, more than 25 million tons of low-density polyethylene (LDPE) are produced annually, which form significant polluting waste streams at end-of-life due to a lack of robust infrastructure for mechanical or chemical recycling. To address this need, researchers pursue biological strategies for LDPE deconstruction. Researchers focus on the microbiomes of yellow mealworms or the larvae of T. molitor as they degrade plastics more rapidly than microbial isolates and do not require clean plastics or pretreatment like mechanical and chemical recycling. While bacterial community members have been identified, the specific pathways responsible for biodegradation remain to be elucidated.
Early project progress confirmed that mealworm diet strongly impacted plastic consumption rates and enriched plastics-modifying microbes. More recently, researchers validated that gut extracts containing this rich microbial community degrade the molecular weight of LDPE films by more than 3-orders of magnitude within a week, confirming the importance of the gut microbiome in plastics degradation. Researchers are currently characterizing these communities via integrated omics analyses at all levels.
To understand the mechanisms by which these microbes degrade LDPE, researchers have isolated a collection of mealworm gut microbes, which were screened for growth on LDPE as a primary carbon source. Faster growing isolates are strongly correlated with increased oxidation of LDPE films via carbonyl insertion, consistent with the hypothesis of promiscuous alkane metabolism for plastics degradation. These isolates were also statistically enriched in peroxidases, oxidases, and other proposed LDPE-degrading enzymes (PEases). Heterologous expression and in vitro testing of candidate PE-ases from these isolates on LDPE films yielded a positive hit that introduces aldehyde groups in LDPE films. In situ inhibition of this enzyme class in the mealworm gut is sufficient to abolish PE deconstruction, suggesting a role in activating plastics degradation. In vitro testing, phylogenetic analysis and simulated protein folding studies of other enzymes that belong to this functional class revealed a sub-clade of active PE-ases that structurally diverges from non-PE degrading enzymes in the same class.
In parallel, researchers also develop photoreactive chemical probes that resemble PE oligomers and have affinity for plastic degrading enzymes for more high throughput discovery. PE probes were validated by evaluating the proteins they bind in commensal isolates from the yellow mealworm. The team is beginning to identify secreted and intracellular proteins that researchers anticipate enable efficient plastics degradation. The studies also demonstrate the potential for live cell probe labeling to enable cell sorting and isolation, which researchers are now pursuing to create functionally enriched plastic degrading consortia.
This work has validated the ability of T. molitor gut extracts to deconstruct PE and developed strong evidence for a critical microbial enzyme that activates PE substrates for deconstruction. Researchers have also developed significant omics resources, microbial isolates and consortia that are beginning to reveal novel strategies and protein structural motifs for enhanced PE degradation. This project generates comprehensive systems-level insight into plastic-degradation pathways and aims to develop design rules for synthetic consortia and enzymes enriched in plastic degradation activity.
Funding Information
This material is based upon work supported by the U.S. DOE, Office of Science, BER Program, GSP under Award Number DE-SC0022018. A portion of this research will be performed under the Facilities Integrating Collaborations for User Science (FICUS) initiative and use resources at the DOE Joint Genome Institute and the Environmental Molecular Sciences Laboratory, which are DOE Office of Science User Facilities. Both facilities are sponsored by the BER Program and operated under Contract Nos. DE-AC02-05CH11231 (JGI) and DE-AC05-76RL01830 (EMSL).