Ester bond pre-activation for high-efficiency biodegradation: A self-reinforcing degradation strategy for PET via an evolved bacterium.

Polyethylene terephthalate (PET) is a hazardous environmental contaminant that contributes to both plastic and microplastic pollution, with its biodegradation severely limited by the kinetic stability of ester bonds-particularly in alkaline industrial wastewater (pH 9-11) where most known biocatalysts are inactive. To overcome this, evolutionary engineering was employed to construct a whole-cell biocatalyst for alkaline environments. Through UV-LiCl mutagenesis and adaptive laboratory evolution, an alkaline-adapted Comamonas testosteroni strain F6 was developed, thriving at pH 10 with PET as sole carbon source. Strain F6 increased weight loss from 2.4% to 6.1% in 3 days and accelerated terephthalic acid release versus the wild-type under neutral conditions. This improvement arises from a synergistic mechanism: alkaline conditions chemically pre-activate ester bonds, and the released monomers fuel microbial growth and enzyme secretion, establishing a self-reinforcing degradation cycle. This feedback-driven process caused severe surface erosion, reducing fiber diameter from 20.2 to 18.1 μm. The system operates at mild pH 10 and 37 °C with a self-moderating effect that partially neutralizes alkalinity, contrasting with harsh chemical hydrolysis (pH >13, high temperature). This work provides a theoretical basis for using substrate pre-activation and evolved biocatalysis to treat PET-contaminated alkaline industrial effluents.