Polyurethanes (PU) are ubiquitous in our daily lives, finding uses in foam sponges, shoe soles, paints and long-lasting building materials and have a global market value of over $57 billion. The broad range of applications for polyurethanes can be attributed to their structural diversity (e.g. ester-based, ether-based). Microorganisms, including various species of bacteria and fungi, are known to biodegrade various forms of polyurethanes. Unwanted microbial PU degradation can have devastating structural and economic effects across multiple sectors including the construction and automotive industries, yet can be a valuable resource to promote PU degradation for recycling industries. Thus, understanding the molecular mechanisms of microbial PU degradation is extremely valuable.
Several Pseudomonas species can naturally degrade PU. A handful of molecular studies have identified polyurethanase enzymes, such as PueA/B, that facilitate the breakdown of polyurethane chains into oligomers and monomers. However, it has been demonstrated that PU degradation can still occur in pueA/B mutants, indicating that additional yet undiscovered enzymes are also involved in the PU biodegradation process. In this study we perform the first functional genome-wide screen to uncover all genes and pathways involved in bacterial PU degradation using the high-throughput technique of transposon insertion sequencing (TIS) on Pseudomonas protegens strain Pf-5.
We performed the TIS screens on different types of polyurethanes and our data confirmed involvement of some expected PU degradation genes, as well as identified novel genes not previously linked to PU degradation. Using Biocyc and KEGG pathway analysis, the genes were mapped onto functional pathways, and several pathways important in PU degradation were illuminated, including fatty acid metabolism and stress tolerance. We then validated the role of novel polyurethane degradation genes by performing microbiological screening assays, spectroscopy and microscopy on targeted mutants.
By creating the first genome-wide map of bacterial PU biodegradation, we can begin to understand how microorganisms break down this fundamental material, allowing us to ultimately prevent unwanted premature biodegradation or improve biodegradation of end-of-life plastics.