Intracellular polyhydroxyalkanoate (PHA) granules are produced naturally by many bacteria as carbon and energy stores. They can be extracted and used as fully biodegradable bioplastics. The monomer composition of the polymer determines techno-functional properties of the material and can be influenced by both cultivation conditions and the genetics of the production strains that drive the metabolic pathways. PHAs have the potential to replace currently used petroleum-based synthetic plastics that are not biodegradable, but a major challenge is higher production costs. Widespread adoption of bioplastics is hindered by the lack of reliable, predictable and inexpensive methods to produce a broad variety of PHA bioplastics. To address this challenge, we are using functional metagenomics-enabled bacterial genome engineering for the efficient valorization of low value food waste and side streams into PHA bioplastics. An example is the engineering of lactose and galactose utilization pathways into Pseudomonas alloputida, coupled with modified PHA synthesis pathways, to convert lactose-rich waste from dairy production to a variety of PHA polymers. This upcycling strategy contributes to circular bioeconomy goals at multiple levels.