Microbial degradation of a widely used model polyethylene is restricted to medium- and long-chain alkanes and their oxidized derivatives

Plastics are widely used materials, yet their chemical stability hinders biodegradation, exacerbating pollution on a global scale. Contaminated soils may foster microbes adapted to degrade plastics or derivatives, and these organisms and their enzymes offer promising avenues for the development of biotechnological recycling strategies. Here, two microbial communities originating from soil collected at a plastic-contaminated site in Norway were enriched to select for bacteria involved in the decomposition of a widely used, model polyethylene (low molecular weight, LMWPE; average carbon chain length of 279). We leveraged genome-resolved metatranscriptomics to identify active populations affiliated with Acinetobacter guillouiae and Pseudomonas sp., showing a suite of upregulated genes (including those encoding alkane 1-monooxygenases, Baeyer-Villiger monooxygenases, and cytochrome P450 monooxygenases) with functions compatible with degradation of medium- and long-chain hydrocarbons and their oxidized derivatives. Spectroscopic, spectrometric and chromatographic analyses revealed the unexpected presence of medium- (C10-16) and long-chain (C17-34) alkanes and 2-ketones in the LMWPE substrate, preventing the erroneous conclusion that the microbial community was degrading the polymeric component. Consistently, only alkanes and 2-ketones of C10-27 were selectively degraded by an A. guillouiae isolate, as confirmed by proteomics analyses and substrate characterization following bacterial growth. Besides extending the knowledge on the enzymatic toolbox of soil-associated microbial systems for degrading alkanes and ketones likely arising from abiotic oxidation of polymeric LMWPE, our results provide an advanced compositional characterization of a widely used model "PE" while offering valuable insight to support future studies aimed at unequivocally identifying organisms and their enzymes implicated in PE transformation.