Defined Microbial Mixed Culture for Utilization of Polyurethane Monomers

The end-of-life plastic crisis is very prominent in the research area and even in the public realm. Especially, for plastic polymers that are difficult to recycle via traditional routes such as the polyurethanes (PUs), novel routes should be investigated. In 2015, PU contributed about 16 million metric tons of global plastic waste. While polymer degradation via chemical routes such as solvolysis and pyrolysis are feasible, the challenge of PU chemical recycling is in the varying mixture and composition of its monomers. Here, we propose a biotechnological route to utilize PU hydrolysate as a carbon source for a defined microbial mixed culture. The mixed culture consists of dedicated microbes, each trained to utilize a single PU monomer and further engineered to produce valuable products. While three Pseudomonas putida KT2440 derivatives utilized adipic acid, 1,4-butanediol, and ethylene glycol, respectively, a recently described Pseudomonas sp. TDA1 used 2,4-toluenediamine (TDA) as a sole carbon source. However, TDA clearly inhibited mixed substrate utilization by the mixed culture, and it also has a high intrinsic value. Therefore, TDA reactive extraction before PU monomer utilization was established, allowing full utilization of the remaining PU monomers as carbon sources for rhamnolipid production. The results highlight the potential of (bio)technological plastic upcycling.