Functional Studies of β-Glucosidases of Cytophaga hutchinsonii and Their Effects on Cellulose Degradation.
Functional Studies of β-Glucosidases of Cytophaga hutchinsonii and Their Effects on Cellulose Degradation.
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哈钦森噬细胞菌β-葡萄糖苷酶的功能研究及其对纤维素降解的影响
DOI：
10.3389/fmicb.2017.00140
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发表时间：
2017
影响因子：
5.2
通讯作者：
Lu X
中科院分区：
文献类型：
--
作者：
Bai X;Wang X;Wang S;Ji X;Guan Z;Zhang W;Lu X
无游离纤维素酶或纤维素体的哈氏细胞噬菌能快速消化结晶纤维素。其细胞接触纤维素降解机制尚不清楚。本研究对哈金梭菌中4个β-葡萄糖苷酶（β-glucosidase, bgl）基因进行了单基因和多基因缺失，并对这些β-葡萄糖苷酶在纤维素二糖和纤维素降解中的功能进行了研究。我们发现组成性表达的BglB在利用纤维素二糖中起关键作用，而由纤维素二糖诱导的BglA可以部分弥补BglB的缺失。双缺失突变体ΔbglA/bglB失去了消化纤维素二糖的能力，不能在纤维素培养基中生长，这表明β-葡萄糖苷酶对纤维素降解很重要。当在纤维素培养基中培养时，野生型在生长初期培养基中有少量葡萄糖积累，而ΔbglA/bglB几乎没有葡萄糖积累。当添加少量葡萄糖时，ΔbglA/bglB开始降解纤维素并在纤维素培养基中生长。我们推测葡萄糖可能是启动纤维素降解所必需的，并且有了额外的葡萄糖，C. hutchinsonii可以在没有β-葡萄糖苷酶的情况下部分利用纤维素。我们还发现，在纤维素中培养时，既有纤维素结合细胞，也有游离细胞。由于hutchinsonii细胞与纤维素的直接接触是纤维素降解所必需的，因此我们推断，方便在环境中探索新领域的游离细胞可能由贴壁细胞供能，这些贴壁细胞可以向环境中产生纤维素低聚糖和葡萄糖。本研究丰富了我们对哈金梭菌纤维素水解途径的认识。
Cytophaga hutchinsonii can 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 in C. hutchinsonii were 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 of bglB. The double deletion mutant ΔbglA/bglB lost 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/bglB started to degrade cellulose and grew in cellulose medium. We inferred that glucose might be essential for initiating cellulose degradation, and with additional glucose, C. hutchinsonii could 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 between C. hutchinsonii cells 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 of C. hutchinsonii.