Polyethylene valorization by combined chemical catalysis with bioconversion by plastic-enriched microbial consortia

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 (C4-C35) 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 by both enriched consortia was a C16-C16 wax ester. Wax esters have considerable industrial value, with the longer chain lengths (C32-C36) having the highest value. We identified two Rhodococcus aetherivorans strains that grow well on C24, indicating 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 polyethylene. SynopsisChemical catalysis can be used to deconstruct polyethylene waste material to produce a mixture of alkanes. Enriched environmental microbial consortia can valorize these polyethylene deconstruction products via functionalization that preserves the alkane chain length thus minimizing CO2 production.