Microbial bioconversion of thermally depolymerized polypropylene by Yarrowia lipolytica for fatty acid production

Plastic production and waste generation will continue to rise as nations worldwide grow economically. In this work, we detail a pyrolysis-based bioconversion process for polypropylene (PP) to produce value-added fatty acids (FAs). PP pellets were depolymerized by pyrolysis, generating oil that consisted of mainly branched chain fatty alcohols and alkenes. The oil was mixed with biodegradable surfactants and trace nutrients and mechanically homogenized. The resulting medium, OP4, was used for fermentation by Yarrowia lipolytica strain 78-003. Y. lipolytica assimilated > 80% of the substrate over 312 h, including 86% of the fatty alcohols. Y. lipolytica produced up to 492 mg L^-1 lipids, compared with 216 mg L^-1 during growth in surfactant-based control medium. C 18 compounds, including oleic acid, linoleic acid, and stearic acid, were the predominant products, followed by C 16 compounds palmitic and palmitoleic acids. Two percent of the products was C 20 compounds. The majority of the products were unsaturated FAs. Growth on hydrophobic substrates (OP4 medium, hexadecane) was compared with growth on hydrophilic substrates (glucose, starch). The resulting FA profiles revealed an absence of short-chain fatty acids during growth on hydrophobic media, findings consistent with ex novo FA biosynthesis. Overall, FA profiles by Y. lipolytica during growth in OP4 medium were similar to FA profiles while growing on natural substrates. The process described here offers an alternative approach to managing postconsumer plastic waste.