The type IX secretion system: Insights into its function and connection to glycosylation in Cytophaga hutchinsonii

The recently discovered type IX secretion system(T9SS)is limited to the Bacteroidetes phylum.Cytophaga hutchin-sonii,a member of the Bacteroidetes phylum widely spread in soil,has complete orthologs of T9SS components and many T9SS substrates.C.hutchinsonii can efficiently degrade crystalline cellulose using a novel strategy,in which bacterial cells must be in direct contact with cellulose.It can rapidly glide over surfaces via unclear mech-anisms.Studies have shown that T9SS plays an important role in cellulose degradation,gliding motility,and ion assimilation in C.hutchinsonii.As reported recently,T9SS substrates are N-or O-glycosylated at their C-terminal domains(CTDs),with N-glycosylation being related to the translocation and outer membrane anchoring of these proteins.These findings have deepened our understanding of T9SS in C.hutchinsonii.In this review,we focused on the research progress on diverse substrates and functions of T9SS in C.hutchinsonii and the glycosylation of its substrates.A model of T9SS functions and the glycosylation of its substrates was proposed.

哈氏噬纤维菌生活史中形态的变化

【目的】研究哈氏噬纤维菌Cytophaga hutchinsonii在生活史中细胞形态的变化。【方法】利用光学显微镜、荧光显微镜和电子扫描显微镜对哈氏噬纤维菌生活状态进行详细观察。【结果】发现在饥饿状态下,长杆状菌体开始逐渐弯曲,菌体两端靠近成环形,环形菌体又进一步盘绕收缩成微小球形体,微小球形体在一定条件下能像生孢噬纤维菌的小孢囊一样萌发形成长杆状菌。另外还观察到哈氏噬纤维菌特殊的类核分裂现象。【结论】首次对哈氏噬纤维形成环形菌体和类似小孢囊的微小球形体的过程进行详细描述,为进一步揭示其形态变化与纤维素降解能力之间的关系提供依据。

微生物降解纤维素的新机制

自然界中能够降解纤维素的微生物分布广泛,纤维素降解的方式也呈现很高的多样性。Cytophaga hutchinsonii属于拟杆菌门,具有很强的结晶纤维素降解能力,但是其降解机制既异于已经发现的游离纤维素酶降解体系,也不同于纤维小体的降解模式,推测其存在第3种细胞结合型纤维素降解模式。本文简要阐述以C.hutchinsonii为代表的一种新的纤维素降解策略。

哈氏噬纤维菌吸附纤维素的影响因素

【目的】探索哈氏噬纤维菌(Cytophaga hutchinsonii)吸附纤维素的作用机制。【方法】通过比较不同因素对哈氏噬纤维菌吸附纤维素的影响,包括:菌龄、pH、温度、表面电荷、细胞活力、细胞表面蛋白、细胞表面多糖以及纤维素类似物等,寻找在吸附过程中起重要作用的细胞成分。【结果】菌体经蛋白酶及热处理,对纤维素的吸附能力完全丧失;叠氮化钠、甲醛和戊二醛处理对菌体吸附能力影响不明显;菌体经刚果红和高碘酸钠处理,吸附能力变化不大;菌体对纤维素底物的吸附具有特异性,吸附作用不受纤维二糖和羧甲基纤维素的抑制。【结论】实验表明,哈氏噬纤维菌吸附纤维素的能力与菌体表面蛋白密切相关,而受细胞的代谢活性和胞外多糖影响较小,推测细胞表面可能存在特异性的纤维素结合蛋白。