Coyne Michael J, Weinacht Katja G, Krinos Corinna M, Comstock Laurie E
Channing Laboratory, Brigham and Women's Hospital, Harvard Medical School, 181 Longwood Avenue, Boston, MA 02115, USA.
Proc Natl Acad Sci U S A. 2003 Sep 2;100(18):10446-51. doi: 10.1073/pnas.1832655100. Epub 2003 Aug 12.
The mammalian gut represents a complex and diverse ecosystem, consisting of unique interactions between the host and microbial residents. Bacterial surfaces serve as an interface that promotes and responds to this dynamic exchange, a process essential to the biology of both symbionts. The human intestinal microorganism, Bacteroides fragilis, is able to extensively modulate its surface. Analysis of the B. fragilis genomic sequence, together with genetic conservation analyses, cross-species cloning experiments, and mutational studies, revealed that this organism utilizes an endogenous DNA inversion factor to globally modulate the expression of its surface structures. This DNA invertase is necessary for the inversion of at least 13 regions located throughout the genome, including the promoter regions for seven of the capsular polysaccharide biosynthesis loci, an accessory polysaccharide biosynthesis locus, and five other regions containing consensus promoter sequences. Bacterial DNA invertases of the serine site-specific recombinase family are typically encoded by imported elements such as phage and plasmids, and act locally on a single region of the imported element. In contrast, the conservation and unique global regulatory nature of the process in B. fragilis suggest an evolutionarily ancient mechanism for surface adaptation to the changing intestinal milieu during commensalism.
哺乳动物的肠道是一个复杂多样的生态系统，由宿主与微生物群落之间独特的相互作用构成。细菌表面作为一个界面，促进并响应这种动态交换，这一过程对共生双方的生物学特性都至关重要。人类肠道微生物脆弱拟杆菌能够广泛调节其表面。对脆弱拟杆菌基因组序列的分析，结合遗传保守性分析、跨物种克隆实验和突变研究，揭示出该生物体利用一种内源性DNA倒位因子来全局调节其表面结构的表达。这种DNA转化酶对于基因组中至少13个区域的倒位是必需的，这些区域包括7个荚膜多糖生物合成位点的启动子区域、一个辅助多糖生物合成位点以及其他5个含有共有启动子序列的区域。丝氨酸位点特异性重组酶家族的细菌DNA转化酶通常由噬菌体和质粒等导入元件编码，并在导入元件的单个区域上局部起作用。相比之下，脆弱拟杆菌中该过程的保守性和独特的全局调节性质表明，这是一种在共生过程中表面适应不断变化的肠道环境的古老进化机制。
