An all-in-one strategy for the simultaneous production of bioplastics and degrading enzymes in engineered Escherichia coli

Bioplastics are promising alternatives for traditional plastics, which contribute significantly to environmental pollution and have a detrimental impact on ecosystems. To advance their use, further research into bioplastic biodegradation is essential. In this study, we propose a novel approach for simultaneous polyhydroxybutyrate (PHB) and degrading enzyme production in a single-cell system using engineered Escherichia coli. Typically, PHB depolymerases, such as PhaZ, disrupt bioplastic synthesis in cells, leading to a self-defeating cycle of production and degradation. To counter this, we introduced synthetic PHB production genes and triacylglycerol lipase (TGL) from Bacillus sp. JY35, along with a native signal peptide for secretion. This enabled PHB accumulation inside the cells while TGL was secreted into the supernatant. The concentrations of PHB produced with and without TGL were similar (31.44 % PHB with TGL and 32.12 % PHB without TGL). TGL was efficiently secreted in E. coli, achieving specific esterase activities of 7.1 U/mg and 15.7 U/mg for p-Nitrophenyl butyrate and p-nitrophenyl octanoate, respectively, and degraded PHB film by 30.1 % over 14 d. Moreover, TGL retained 86 % and 91 % of its activities for the C4 and C8 substrates, respectively, after 30 d of storage at room temperature, suggesting potential use PHB degradation after use. Our study demonstrates a straightforward one-month circular cycle for bioplastic production and degradation by a single producer.