As nature’s ‘recyclers’, actinobacteria reside in the soil, secreting enzymes to break down their surroundings and returning nutrients to the soil to sustain the cycle of life. Scientists have uncovered something surprising about these microscopic powerhouses: their enzymes can also degrade some of the most stubborn pollutants on Earth.
Enzymes such as cutinases and hydrolases from actinobacteria can be harnessed to break down polyethylene terephthalate (PET)—a plastic commonly used in water bottles and packaging that is notoriously difficult to recycle. These enzymes reduce PET into simpler, non-plastic molecules that can be further processed or biodegraded.
A multidisciplinary team led by Yee Hwee Lim and Fong Tian Wong worked to explore how these unique bacteria might bridge gaps in existing PET recycling technologies. The team consisted of colleagues across science and engineering and biology disciplines from A*STAR’s Institute of Molecular and Cell Biology (IMCB) and Institute of Sustainability for Chemicals, Energy and Environment (ISCE2). “We drew inspiration from this bacterial family to expand our research into PET degradation, leveraging our expertise and a newly developed in-house platform for protein construction and testing,” said Wong.
The researchers delved into actinobacterial genomic data, targeting enzymes from Microbispora, Nonomuraea and Micromonospora. The team identified, engineered and tested these enzymes to evaluate their ability to decompose PET. Although these genera are known for breaking down complex molecules in diverse environments, this is the first example demonstrating that they also contain enzymes that can depolymerise PET. Analyses of the by-products confirmed that certain enzymes effectively reduced PET not just into smaller fragments but transformed it back into its original monomers; this can then be used for making PET (completing the cycle) or upcycled into other products.
The team found that a selection of enzymes can degrade PET at mild temperatures and neutral pH—conditions that are less energy-intensive than traditional mechanical recycling methods and more environmentally friendly than chemical processes. "By breaking down plastics to monomers, bio-based recycling not only aligns with eco-friendly practices but also simplifies the production chain, filling the gaps left by current recycling technologies," Wong remarked.
Wong highlighted that these enzymes and their host organisms, actinobacteria, may be pivotal in real-world sustainability efforts by offering energy-efficient and non-toxic bio-based solutions that utilise water-based and low-temperature processes. They can also facilitate long-term waste management strategies, such as the integration of anaerobic digesters for handling mixed waste.
The researchers have patented their technology and are expanding their work through the Accelerated Design & Engineering Platform (ADEPT) for enzymes, which supports the rapid construction and testing of proteins, enabling advances in microbial and enzymatic solutions.
"Witnessing the incredible abilities of microbes and enzymes in action gives us hope for a more sustainable future," Wong concluded.
The A*STAR-affiliated researchers contributing to this research are from the Institute of Sustainability for Chemicals, Energy and Environment (ISCE2) and Institute of Molecular and Cell Biology (IMCB).
