Decoding PHA depolymerase activity: A methodological overview

Polyhydroxyalkanoates (PHAs) are microbial polyesters that have emerged as promising sustainable alternatives to conventional plastics. In nature, these polymers are degraded by microorganisms through the action of specific enzymes known as PHA depolymerases. Beyond their physiological role in microbial carbon metabolism, these enzymes have attracted increasing interest as potential tools for enzymatic recycling and controlled depolymerization of PHA materials. However, studying the activity of PHA depolymerases remains experimentally challenging due to the complex physicochemical nature of PHA substrates and the diversity of assay formats used in the literature. Over the past decades, a wide range of qualitative and quantitative methods have been developed to evaluate depolymerase activity, including plate-based assays, turbidity measurements, spectrophotometric methods using synthetic substrates, and analytical techniques for identifying hydrolysis products. Importantly, the apparent activity of these enzymes strongly depends on the physical state of the polymer substrate, including crystallinity, particle size, and surface structure, which complicates the comparison of results across studies. In this work, we compile and critically analyse the experimental approaches currently used to characterize PHA depolymerases. By bringing together methodologies scattered throughout the literature, we aim to provide a practical reference for researchers investigating the enzymology of PHA degradation and the potential application of depolymerases in enzymatic polymer recycling.