One-Pot Biosynthesis of Acetone from Waste Poly(hydroxybutyrate)

The plastic waste crisis is catalyzing change across the plastics life cycle. Central to this is increased production and application of bioplastics and biodegradable plastics. In particular, poly(hydroxybutyrate) (PHB) is a biodegradable bioplastic that can be produced from various renewable and waste feedstocks and is a promising alternative to some petrochemical-derived and non-biodegradable plastics. Despite its advantages, PHB biodegradation depends on environmental conditions, and the effects of degradation into microplastics, oligomers, and the 3-hydroxybutyrate (3-HB) monomer on soil microbiomes are unknown. We hypothesized that the ease of PHB biodegradation renders this next-generation plastic an ideal feedstock for microbial recycling into platform chemicals currently produced from fossil fuels. To demonstrate this, we report the one-pot degradation and recycling of PHB into acetone using a single strain of engineered <i>Escherichia coli</i>. Following strain development and initial bioprocess optimization, we report maximum titers of 123 mM acetone (7 g/L) from commercial PHB granules after 24 h fermentation at 30 °C. We further report biorecycling of an authentic sample of post-consumer PHB waste at a preparative scale. This is the first demonstration of biological recycling of PHB into a second-generation chemical, and it demonstrates next-generation plastic waste as a novel feedstock for the circular bioeconomy.