Researchers at Korea Advanced Institute of Science and Technology (KAIST) have shown that microorganisms can be used to create a bio-based alternative to petroleum-based materials used in hot-melt adhesives (HMAs). These adhesives are commonly used in packaging, furniture, electronics, and the automotive industry. The team, led by Distinguished Professor Sang Yup Lee from the Department of Chemical and Biomolecular Engineering, engineered Escherichia coli bacteria to produce a new type of biodegradable polymer called aromatic polyhydroxyalkanoate (PHA) from glucose. This polymer has adhesive and thermal properties suitable for use as a hot-melt adhesive. The findings were published in the journal Nature Communications. Hot-melt adhesives are solid materials that are melted using heat and then solidify upon cooling to bond surfaces together. They are favored in industry because they do not require solvents and allow for quick bonding. However, most current HMAs are made from petroleum-derived polymers like ethylene-vinyl acetate (EVA), which are not easily biodegradable and can lead to environmental issues such as waste and microplastics. Even when biodegradable packaging is used, the presence of non-degradable adhesives can reduce the overall sustainability of the product. To address this, the researchers focused on PHA, a type of biodegradable polymer that microorganisms can produce using renewable resources like glucose. PHA’s properties—such as flexibility, strength, and heat resistance—can be adjusted by varying the components and proportions in the polymer. By incorporating 4-hydroxybutyrate (4HB), which adds softness and adhesion, and phenyllactate (PhLA), which increases rigidity and heat resistance, the team created two new PHA-based polymers: poly(4HB-co-PhLA) and poly(3HB-co-4HB-co-PhLA). Adjusting the ratios of these components allowed the researchers to fine-tune the adhesion and thermal performance of the materials, with the best adhesive results observed when the polymers contained 24–34 mol% of 4HB. The team engineered E. coli to consume glucose and produce the necessary monomers, which are then linked into polymers. To overcome metabolic challenges, they adjusted gene expression timing, added a specific enzyme called CoA transferase, and used a genome-scale model to optimize the metabolic pathways. Using a fed-batch fermentation process, they successfully produced up to 10.2 grams per liter of poly(4HB-co-PhLA) and 52.8 grams per liter of poly(3HB-co-4HB-co-PhLA). In testing, the polymers showed adhesive performance comparable to commercial EVA adhesives and retained their strength even after repeated heating and re-bonding. The inclusion of PhLA also improved the materials’ heat resistance. Additionally, the polymers were found to be biodegradable, as treatment with lipase—an enzyme that breaks down fats—caused surface degradation and reduced their molecular weight. This suggests that the new PHA materials can be broken down naturally. The research highlights the potential of metabolic engineering to create functional materials with customizable properties. Moving forward, this approach could be used to produce a wide range of sustainable polymers from renewable resources, reducing reliance on petrochemical processes. As Professor Lee noted, this work demonstrates that engineering microbial metabolism can enable the direct production of functional materials, opening the door to broader biomanufacturing applications.