Identification of a Novel Thermal Promoter and Its Application in Glutamate Decarboxylase Protein Expression in Bacillus licheniformis.

As a thermotolerant bacterium, Bacillus licheniformis is an attractive chassis for high-temperature biomanufacturing. Here, we identified a novel temperature-responsive promoter, PycgM, which maintained strong transcriptional activity at 37-52 °C. In a promoter-mCherry reporter system, PycgM exhibited 2287.3-fold higher activity than P2 at 52 °C, demonstrating excellent compatibility with a thermotolerant host. Truncation analysis identified a 150-bp core functional region responsible for optimal activity under induction and heat stress. When applied to drive glutamate decarboxylase expression at 50 °C, PycgM enabled γ-aminobutyric acid production of 391.67 g/L with a 98.69% conversion rate, representing a 275% increase over 37 °C fermentation. The whole-cell biocatalyst retained 86% activity after five reuse cycles, and SEM analysis indicated acceptable structural stability despite moderate morphological changes. These results demonstrate that PycgM is a robust, high-temperature genetic element for efficient enzyme and metabolite production in thermotolerant hosts.