title: Functional Studies of β-Glucosidases ofCytophaga hutchinsoniiand Their Effects on Cellulose Degradation.
abstract: Cytophaga hutchinsoniican rapidly digest crystalline cellulose without free cellulases or cellulosomes. Its cell-contact cellulose degradation mechanism is unknown. In this study, the four β-glucosidase (bgl) genes inC. hutchinsoniiwere singly and multiply deleted, and the functions of these β-glucosidases in cellobiose and cellulose degradation were investigated. We found that the constitutively expressed BglB played a key role in cellobiose utilization, while BglA which was induced by cellobiose could partially make up for the deletion ofbglB. The double deletion mutant ΔbglA/bglBlost the ability to digest cellobiose and could not thrive in cellulose medium, indicating that β-glucosidases were important for cellulose degradation. When cultured in cellulose medium, a small amount of glucose accumulated in the medium in the initial stage of growth for the wild type, while almost no glucose accumulated for ΔbglA/bglB. When supplemented with a small amount of glucose, ΔbglA/bglBstarted to degrade cellulose and grew in cellulose medium. We inferred that glucose might be essential for initiating cellulose degradation, and with additional glucose,C. hutchinsoniicould partially utilize cellulose without β-glucosidases. We also found that there were both cellulose binding cells and free cells when cultured in cellulose. Since direct contact betweenC. hutchinsoniicells and cellulose is necessary for cellulose degradation, we deduced that the free cells which were convenient to explore new territory in the environment might be fed by the adherent cells which could produce cello-oligosaccharide and glucose into the environment. This study enriched our knowledge of the cellulolytic pathway ofC. hutchinsonii.
authors.affiliation: State Key Laboratory of Microbial Technology, School of Life Science, Shandong University Jinan, China.
authors.forename: Xinfeng
authors.initials: X
authors.lastname: Bai
authors.affiliation: State Key Laboratory of Microbial Technology, School of Life Science, Shandong University Jinan, China.
authors.forename: Xifeng
authors.initials: X
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Microbial Technology, School of Life Science, Shandong University Jinan, China.
authors.forename: Sen
authors.initials: S
authors.lastname: Wang
authors.affiliation: Department of Pathogenic Biology, Binzhou Medical University Yantai, China.
authors.forename: Xiaofei
authors.initials: X
authors.lastname: Ji
authors.affiliation: State Key Laboratory of Microbial Technology, School of Life Science, Shandong University Jinan, China.
authors.forename: Zhiwei
authors.initials: Z
authors.lastname: Guan
authors.affiliation: State Key Laboratory of Microbial Technology, School of Life Science, Shandong University Jinan, China.
authors.forename: Weican
authors.initials: W
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of Microbial Technology, School of Life Science, Shandong University Jinan, China.
authors.forename: Xuemei
authors.initials: X
authors.lastname: Lu
keywords: Cytophaga hutchinsonii; cellobiose; cellulose; degradation; β-glucosidase