Cytophaga hutchinsonii gldN , Encoding a Core Component of the Type IX Secretion System, Is Essential for Ion Assimilation, Cellulose Degradation, and Cell Motility

The widespread Gram-negative bacterium Cytophaga hutchinsonii uses a novel but poorly understood strategy to utilize crystalline cellulose. Recent studies showed that a T9SS exists in C. hutchinsonii and is involved in cellulose degradation and motility. However, the main components of the C. hutchinsonii T9SS and their functions are still unclear. Our study characterized the function of GldN, which is a core component of the T9SS. GldN was proved to play vital roles in cellulose degradation and cell motility. Notably, GldN is essential for the acquisition of Ca 2+ and Mg 2+ ions under Ca 2+ - and Mg 2+ -deficient conditions, revealing a link between the T9SS and the metal ion transport system. The outer membrane abundance of CHU_2807, which is essential for Ca 2+ and Mg 2+ uptake in PY6 medium, was affected by the deletion of GldN. This study demonstrated that the C. hutchinsonii T9SS has extensive functions, including cellulose degradation, motility, and metal ion assimilation, and contributes to further understanding of the function of the T9SS in the phylum Bacteroidetes .