Deletion of a Gene Encoding a Putative Peptidoglycan-Associated Lipoprotein Prevents Degradation of the Crystalline Region of Cellulose in Cytophaga hutchinsonii

Abstract

<i>Cytophaga hutchinsonii</i> is a gliding Gram-negative bacterium in the phylum <i>Bacteroidetes</i> with the capability to digest crystalline cellulose rapidly, but the mechanism is unclear. In this study, deletion of <i>chu_0125</i>, encoding a homolog of the peptidoglycan-associated lipoprotein (Pal), was determined to prevent degradation of the crystalline region of cellulose. We found that the <i>chu_0125</i> deletion mutant grew normally in regenerated amorphous cellulose medium but displayed defective growth in crystalline cellulose medium and increased the degree of crystallinity of Avicel. The endoglucanase and β-glucosidase activities on the cell surface were reduced by 60 and 30% without <i>chu_0125</i>, respectively. Moreover, compared with the wild type, the <i>chu_0125</i> deletion mutant was found to be more sensitive to some harmful compounds and to release sixfold more outer membrane vesicles (OMVs) whose protein varieties were dramatically increased. These results indicated that CHU_0125 played a critical role in maintaining the integrity of the outer membrane. Further study showed that the amounts of some outer membrane proteins were remarkably decreased in the <i>chu_0125</i> deletion mutant. Western blotting revealed that CHU_3220, the only reported outer membrane protein that was necessary and specialized for degradation of the crystalline region of cellulose, was largely leaked from the outer membrane and packaged into OMVs. We concluded that the deletion of <i>chu_0125</i> affected the integrity of outer membrane and thus influenced the localization of some outer membrane proteins including CHU_3220. This might be the reason why deletion of <i>chu_0125</i> prevented degradation of the crystalline region of cellulose.