Centre for Infection and Immunity, School of Medicine, Dentistry and Biomedical Sciences, Queen's University Belfast, Medical Biology Centre, 97 Lisburn Road, Belfast BT9 7BL, UK.
Institute of Cell Biology, University of Edinburgh, Darwin Building, Kings Buildings, Edinburgh EH9 3JR, UK.
Microbiology (Reading). 2010 Nov;156(Pt 11):3255-3269. doi: 10.1099/mic.0.042978-0. Epub 2010 Sep 9.
Comparison of the complete genome sequence of Bacteroides fragilis 638R, originally isolated in the USA, was made with two previously sequenced strains isolated in the UK (NCTC 9343) and Japan (YCH46). The presence of 10 loci containing genes associated with polysaccharide (PS) biosynthesis, each including a putative Wzx flippase and Wzy polymerase, was confirmed in all three strains, despite a lack of cross-reactivity between NCTC 9343 and 638R surface PS-specific antibodies by immunolabelling and microscopy. Genomic comparisons revealed an exceptional level of PS biosynthesis locus diversity. Of the 10 divergent PS-associated loci apparent in each strain, none is similar between NCTC 9343 and 638R. YCH46 shares one locus with NCTC 9343, confirmed by mAb labelling, and a second different locus with 638R, making a total of 28 divergent PS biosynthesis loci amongst the three strains. The lack of expression of the phase-variable large capsule (LC) in strain 638R, observed in NCTC 9343, is likely to be due to a point mutation that generates a stop codon within a putative initiating glycosyltransferase, necessary for the expression of the LC in NCTC 9343. Other major sequence differences were observed to arise from different numbers and variety of inserted extra-chromosomal elements, in particular prophages. Extensive horizontal gene transfer has occurred within these strains, despite the presence of a significant number of divergent DNA restriction and modification systems that act to prevent acquisition of foreign DNA. The level of amongst-strain diversity in PS biosynthesis loci is unprecedented.
将最初从美国分离的脆弱拟杆菌 638R 的全基因组序列与在英国(NCTC 9343)和日本(YCH46)分离的两个先前测序的菌株进行比较。尽管 NCTC 9343 和 638R 表面 PS 特异性抗体之间缺乏交叉反应性,但在所有三个菌株中都确认存在 10 个包含与多糖 (PS) 生物合成相关基因的基因座,每个基因座都包含一个推定的 Wzx 翻转酶和 Wzy 聚合酶。基因组比较显示出 PS 生物合成基因座多样性的异常水平。在每个菌株中明显存在的 10 个不同的 PS 相关基因座中,NCTC 9343 和 638R 之间没有相似之处。YCH46 与 NCTC 9343 共享一个位点,通过 mAb 标记证实,与 638R 共享另一个不同的位点,这使得三个菌株之间共有 28 个不同的 PS 生物合成基因座。在 638R 中观察到的 NCTC 9343 中相变异构大荚膜(LC)的表达缺失,很可能是由于点突变导致在推定的起始糖基转移酶内产生一个终止密码子,这对于 NCTC 9343 中 LC 的表达是必需的。还观察到其他主要序列差异来自不同数量和种类的插入外染色体元件,特别是前噬菌体。尽管存在大量不同的可移动基因转移限制和修饰系统,以防止获得外源 DNA,但这些菌株中仍发生了广泛的水平基因转移。在 PS 生物合成基因座中,菌株间的多样性水平是前所未有的。