Enhancement of heat resistance of Bacillus thermoamylovorans drives enhanced PET degradation.

Microbial polyethylene terephthalate (PET) degradation has emerged as an environmentally friendly approach to reducing plastic pollution, but microbial activity is often limited by the high temperatures (60-70 °C) required for efficient degradation. In this study, six endogenous thermotolerant genes were identified in the PET-degrading strain Bacillus thermoamylovorans JQ3. Overexpression of the genes hrcA, hsp20A, and hsp20B significantly enhanced thermotolerance in Escherichia coli, which increased cell viability by >24.2% at temperatures above 40 °C. Similarly, overexpression of hsp20A in B. thermoamylovorans (B. th_Hsp20A) improved its thermotolerance, increasing cell viability by 46.8% at 50 °C and 69.8% at 60 °C. The hsp20A-encoded protein was identified as a small heat shock protein (sHSP). B. th_Hsp20A exhibited significantly improved PET degradation at 60 °C compared with 50 °C, which released 282 µg of terephthalic acid after 7 days of incubation, representing an 84.3% increase compared with the wildtype strain (153 µg). These results highlight that the overexpression of thermotolerant proteins, particularly sHSPs, significantly enhances microbial PET degradation under high-temperature conditions, offering a novel pathway for enhancing microbial PET waste degradation.