Enhancement of cellulosome expression by deletion of an HtrA protein in Clostridium thermocellum.

Clostridium thermocellum efficiently degrades lignocellulosic biomass via cellulosomes, which are secreted dynamic multi-enzyme complexes, making it valuable in the biomass refinery for the production of biofuels and biomaterials. However, the demand for high-level expression of cellulosomes in biorefinery applications presents significant challenges due to their complex composition and intricate regulation mechanism. In this study, deleting the htrA1 gene, which encodes a periplasmic serine protease HtrA1 anchored to the cell membrane, in C. thermocellum was found to be able to significantly enhance cellulosome production while maintaining their specific activity and cell growth. Major cellulosomal components showed much higher expression levels in the extracellular supernatant proteins of the htrA1-deleted strain than in the control strain. The htrA1-deleted strain showed a substantially enhanced cellulose saccharification performance. These findings offer novel insights into the post-translational regulation of cellulosomes and introduce innovative strategies for enhancing whole-cell catalysts used in lignocellulose bioconversion.