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

The type IX secretion system (T9SS), which is involved in pathogenicity, motility, and utilization of complex biopolymers, is a novel protein secretion system confined to the phylum , a common cellulolytic soil bacterium belonging to the phylum , can rapidly digest crystalline cellulose using a novel strategy. In this study, the deletion mutant of () was obtained using PY6 medium supplemented with Stanier salts. GldN was verified to be a core component of T9SS, and is indispensable for cellulose degradation, motility, and secretion of C-terminal domain (CTD) proteins. Notably, the Δ mutant showed significant growth defects in Ca- and Mg-deficient media. These growth defects could be relieved by the addition of Ca or Mg The intracellular concentrations of Ca and Mg were markedly reduced in Δ These results demonstrated that GldN is essential for the acquisition of trace amounts of Ca and Mg, especially for Ca Moreover, an outer membrane efflux protein, CHU_2807, which was decreased in abundance on the outer membrane of Δ, is essential for normal growth in PY6 medium. The reduced intracellular accumulation of Ca and Mg in the Δ mutant indicated that CHU_2807 is involved in the uptake of trace amounts of Ca and Mg This study provides insights into the role of T9SS in metal ion assimilation in The widespread Gram-negative bacterium uses a novel but poorly understood strategy to utilize crystalline cellulose. Recent studies showed that a T9SS exists in and is involved in cellulose degradation and motility. However, the main components of the 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 and Mg ions under Ca- and Mg-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 and Mg uptake in PY6 medium, was affected by the deletion of GldN. This study demonstrated that the 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 .