Enhancing polypropylene bioconversion and lipogenesis by Yarrowia lipolytica using a chemical/biological hybrid process

Plastic waste can serve as a feedstock for microbial bioconversion using a chemical/biological hybrid strategy. We developed a polypropylene (PP) upcycling process that coupled pyrolysis with bioconversion by the oleaginous yeast Yarrowia lipolytica. Using virgin PP, we optimized pH, inoculum density, C/N ratio, and osmolarity and increased the fatty acid titer nearly four-fold to 1.9 g L-1, with 41 percent cellular fatty acid content, the highest content reported to date for plastic-to-lipid microbial bioconversion. The highest fatty acid titer was achieved with an inoculum density of 3 (OD 600 nm), pH = 6.0 and C/N ratio of 80:1. Increasing the medium osmolarity by adding sodium chloride adversely affected cell growth and did not improve the fatty acid titer. The maximum fatty acid titer occurred under conditions that balanced cell growth versus lipogenesis. Using post-consumer PP, the fatty acid titer was significantly lower (0.13 g L-1). Overall, the work demonstrates the potential and the challenges associated with microbial bioconversion of plastics.

Automated summary

Plastic waste can be utilized for microbial bioconversion through a chemical/biological hybrid strategy. By coupling pyrolysis with bioconversion, it is possible to optimize conditions and balance cell growth versus lipogenesis, achieving higher fatty acid titers. However, the conversion of post-consumer PP resulted in significantly lower fatty acid titers, highlighting the challenges associated with microbial bioconversion of plastics.