Polyethylene Valorization by Combined Chemical Catalysis with Bioconversion by Plastic-Enriched Microbial Consortia
Gwendolyn J. Gregory, Cong Wang, Sunitha Sadula, Sam Koval, Raúl F. Lobo, Dionisios G. Vlachos, Eleftherios T. Papoutsakis
Abstract
There are few reports of microbial deconstruction or functionalization of the recalcitrant backbone of polyolefins. However, microbes can utilize polyolefin deconstruction products, including n -alkanes. Here, we combined chemical catalysis with bioconversion to valorize polyethylene (PE) deconstruction products. High-density PE (HDPE) was deconstructed via hydrogenolysis over a ruthenium on carbon catalyst. The resulting n -alkane mixture (C 4 –C 35 ) was utilized as a feedstock for microbial consortia derived from soil from local recycling plants. We found two consortia that utilized the PE-deconstruction product mix as a sole carbon source. We adapted the consortia on a commercially available n -alkane mix to reduce the number of species present and enrich for enhanced alkane utilization. Both resulting enriched consortia utilized the PE-deconstruction product mix more effectively than the original (parent) consortia. The predominant metabolite produced from a model alkane hexadecane by both enriched consortia was a C 16 –C 16 wax ester. Wax esters have considerable industrial value, with longer chain lengths (C 32 –C 36 ) having the highest value. We identified two Rhodococcus aetherivorans strains that grow well on C 24, indicating that this species is important for the functionalization of long-chain alkanes. This work demonstrates that enriched consortia from plastic-enriched environments can be combined with chemical catalysis to valorize PE.