Immobilization of alkaline polygalacturonate lyase from Bacillus subtilis on the surface of bacterial polyhydroxyalkanoate nano-granules

Alkaline polygalacturonate lyase (PGL), one of the pectinolytic enzymes, has been widely used for the bioscouring of cotton fibers, biodegumming, and biopulp production. In our study, PGL from Bacillus subtilis was successfully immobilized on the surface of polyhydroxyalkanoate (PHA) nanogranules by fusing PGL to the N-terminal of PHA synthase from Ralstonia eutropha via a designed linker. The PGL-decorated PHA beads could be simply achieved by recombinant fermentation and consequent centrifugation. The fused PGL occupied 0.985% of the total weight of purified PHA granules, which was identified by mass spectrometer-based quantitative proteomics. The activity of immobilized PGL (184.67 U/mg PGL protein) was a little lower than that of the free PGL (215.93 U/mg PGL protein). The immobilization process did not affect the optimal pH and the optimal temperature of the PGL, but it did enhance the thermostability as well as the pH stability at certain conditions, which will extend the practicability of the immobilized PGL-PHA beads in the alkaline and generally harsh bioscouring process. Furthermore, the immobilized PGL still retained more than 60% of its initial activity after 8 cycles of reuse. Our study provided a novel and promising approach for cost-efficient in vivo PGL immobilization, contributing to wider commercialization of this environmental-friendly biocatalyst.