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Catalytic Bacterial Nanocellulose Composite That Captures and Degrades PET Microplastics
Summary
Scientists have created a plant-based fiber filter with built-in enzymes that can trap plastic bottle microplastics (PET) and actually break them down, rather than just moving them from wastewater into sludge that often ends up back in soil and water. This matters because current treatment plants remove most microplastics from water, but the trapped plastic doesn't go away—it's just relocated, potentially recontaminating the environment and our food and water supply. While this filter is still a proof-of-concept, it could eventually be scaled up into treatment plants to actually destroy microplastic pollution instead of just shuffling it around.
Abstract Microplastic (MP) pollution is a growing environmental concern, with wastewater treatment plants (WWTPs) serving as a critical yet insufficient barrier. Although WWTPs can remove up to 99% of MPs from influent streams, a large fraction of the sequestered MPs is concentrated into sewage sludge and subsequently redistributed to soil and waterways via biosolids. Here, we report a biosynthetic approach to address MP redistribution by coupling microplastic removal with catalytic depolymerization, using enzyme-functionalized bacterial nanocellulose (BNC) filtration materials. As a proof-of-concept, we fused a cellulose-binding domain (CBD) to the thermostable PET hydrolase HotPETase, creating a bifunctional protein, CBD-PETase, that binds to a BNC scaffold and degrades PET microplastic (µPET) captured within the scaffold. We showed that BNC-CBD-PETase composites sequestered irregularly shaped µPET within hierarchical pore networks and generated PET degradation products proportionally to enzyme loading. We further established a co-culture strategy, in which Saccharomyces cerevisiae was engineered to secrete CBD-PETase during BNC scaffold biosynthesis by Komagataeibacter xylinus , which enabled one-pot fabrication of an active BNC-CBD-PETase composite without separate protein purification. Notably, co-culture-derived BNC-CBD-PETase composites retained catalytic activity for at least 24 weeks under dry, ambient storage. This platform provides a route towards a scalable and renewable filtration material with the potential for integration across multiple treatment stages within WWTPs.