Polyhydroxyalkanoates production by yeasts - Still possible?

Synthetic polymers have become ubiquitous in modern life due to their versatility, durability and low production costs, leading to a significant increase in global plastic consumption. However, their widespread use has led to serious environmental problems such as persistent pollution, biodiversity loss, health risks, and contributions to climate change. This highlights the urgent need for sustainable alternatives and improved waste management. Bioplastics currently account for only around 1 % of global plastics production, but their market share is growing. Among the biopolymer alternatives, polyhydroxyalkanoates (PHAs) are particularly attractive because they are microbially synthesized, bio-based, and biodegradable polyesters with a broad range of physical and thermoplastic properties, some of which are comparable to those of petroleum-derived polymers. To date, bacterial systems remain the dominant, most efficient, and industrially established platforms for PHA production, achieving substantially higher titres, yields, and productivities than yeast-based systems. Recent studies have nevertheless identified yeasts as promising alternative hosts for the production of PHA homo- and heteropolymers. Yeasts offer advantages such as metabolic versatility and the ability to utilise diverse substrates, and they may support both PHA synthesis and degradation. However, their current application remains at an early stage and is constrained by lower PHA production than in well-established bacterial hosts, as well as limited understanding and optimisation of the relevant metabolic and regulatory pathways. Advances in genetic engineering and artificial intelligence technologies may help overcome some of these barriers. These tools have not yet been widely applied directly to PHA-producing yeasts. They are discussed here primarily as promising emerging approaches for predictive strain design and bioprocess optimisation, as their direct application to yeast-based PHA production remains limited. This review summarises current knowledge on PHA synthesis in yeasts and discusses key limitations, technological bottlenecks, and future research directions needed for yeasts to become competitive PHA production platforms.