Process integration of enzymatic and microbial PBAT conversion with a Pseudomonas taiwanensis mixed culture

Abstract

Enzymatic depolymerization of polyesters has been established as green recycling strategy to reduce plastic pollution. However, applied on industrially relevant mixed plastic waste, it generates a wide mixture of various oligomers and monomers, complicating downstream processing and monomer recycling. Several Pseudomonas taiwanensis strains have been engineered to grow on plastic monomers while producing valuable aromatics. This enables metabolic funneling of diverse monomers, supporting efficient bio-upcycling. Integrating hydrolysis and monomer conversion into one intensified process would increase the competitiveness of biotechnological upcycling. Therefore, a one-pot process was developed in which hydrolysis of poly(butylene adipate-co-terephthalate) (PBAT) via a cutinase from Humicola insolens (HiC) was coupled with cultivation of P. taiwanensis strains metabolizing the resulting monomers, adipic acid (AA), terephthalic acid (TA) and 1,4-butanediol (BDO). For this purpose, the buffer strength and stirring rate for PBAT-hydrolysis were adjusted for compatibility with cultivation of P. taiwanensis. An impact of various process settings on enzymatic hydrolysis was found with the temperature as main parameter, where enzymatic and microbial conversion conflict. Hence, two consecutive steps were carried out within one reactor—a 24-h hydrolysis at 70 °C, followed by inoculation with Pseudomonas after changing the conditions to 30 °C. Growth on PBAT was established this way, but the TA metabolism was strongly inhibited by the hydrolysate compared to pure TA. This is probably due to an inhibitory effect of AA and TA-containing oligomers on TA uptake or metabolism. After 10 days, all PBAT monomers were completely consumed, setting the path for a novel, industrially promising plastic upcycling concept.