From Waste to Bioplastics: Integrated Approaches for Polyhydroxyalkanoates Production Using Wild Type and Engineered Microorganisms

Polyhydroxyalkanoates (PHAs) are fully biodegradable and biocompatible polyesters synthesized by certain microorganisms as intracellular carbon and energy storage granules. Due to their plastic-like properties, they are considered a promising alternative to fossil plastics. However, their broader commercial use is hindered by high production costs, primarily due to the expensive carbon-rich feedstocks and the process conditions required for microbial fermentation. To address these constraints, efforts have focused on utilizing cheap and readily available materials, such as food and agricultural residues, as alternative carbon sources. A key challenges is the lack of naturally occurring microbial strains capable of both efficiently metabolizing these complex substrates and producing PHAs in high yields. To overcome this limitation, the Microbiology group at DAFNAE explored several innovative strategies including: A) the genetic engineering of Cupriavidus necator DSM545, one of the most effective PHAs-producing strains, to enable utilization of cheap substrates such as lactose-, lipid-rich or starchy residues. B) the enzymatic pre-treatment of substrates, such as applying β-galact osidase to whey. C) the exploitation of anaerobic digestion for substrate pre-treatment to convert waste biomass into volatile fatty acids, which served as effective carbon sources for PHAs synthesis by C. necator DSM545. In addition, to overcome the limitations associated with the high costs linked to sterile fermentations, recent research has turned to extremophile microorganisms as promising alternative PHAs accumulators. These organisms thrive in extreme environmental conditions, offering a natural barrier against contamination and reducing the need for stringent sterilization. This approach seeks to merge the valorization of nutrient-rich agro-industrial waste, such as distilled wine lees, with the unique metabolic capabilities of extremophiles, developing a sustainable and economically feasible process for PHAs production. Although further research is needed to optimize production yields, the approaches described offer promising pathways for industrial-scale PHA production and contribute to more sustainable waste management strategies.