Russo T A, Wenderoth S, Carlino U B, Merrick J M, Lesse A J
Department of Medicine, and The Center for Microbial Pathogenesis, SUNY at Buffalo, New York 14215, USA.
J Bacteriol. 1998 Jan;180(2):338-49. doi: 10.1128/JB.180.2.338-349.1998.
Group III capsular polysaccharides (e.g., K54) of extraintestinal isolates of Escherichia coli, similar to group II capsules (e.g., K1), are important virulence traits that confer resistance to selected host defense components in vitro and potentiate systemic infection in vivo. The genomic organization of group II capsule gene clusters has been established as a serotype-specific region 2 flanked by regions 1 and 3, which contain transport genes that are highly homologous between serotypes. In contrast, the organization of group III capsule gene clusters is not well understood. However, they are defined in part by an absence of genes with significant nucleotide homology to group II capsule transport genes in regions 1 and 3. Evaluation of isogenic, TnphoA-generated, group III capsule-minus derivatives of a clinical blood isolate (CP9, O4/K54/H5) has led to the identification of homologs of the group II capsule transport genes kpsDMTE. These genes and their surrounding regions were sequenced and analyzed. The genomic organization of these genes is distinctly different from that of their group II counterparts. Although kps(K54)DMTE are significantly divergent from their group II homologs at both the DNA and protein levels phoA fusions and computer-assisted analyses suggest that their structures and functions are similar. The putative proteins Kps(K54)M and Kps(K54)T appear to be the integral membrane component and the peripheral ATP-binding component of the ABC-2 transporter family, respectively. The putative Kps(K54)E possesses features similar to those of the membrane fusion protein family that facilitates the passage of large molecules across the periplasm. At one boundary of the capsule gene cluster, a truncated kpsM (kpsM(truncated) and its 5' noncoding regulatory sequence were identified. In contrast to the complete kps(K54)M, this region was highly homologous to the group II kpsM. Fifty-three base pairs 3' from the end of kpsM(truncated) was a sequence 75% homologous to the 39-bp inverted repeat in the IS110 insertion element from Streptomyces coelicolor. Southern analysis established that two copies of this element are present in CP9. These findings are consistent with the hypothesis that CP9 previously possessed group II capsule genes and acquired group III capsule genes via IS110-mediated horizontal transfer.
大肠杆菌肠道外分离株的III型荚膜多糖（如K54），与II型荚膜（如K1）相似，是重要的毒力特征，在体外赋予对特定宿主防御成分的抗性，并在体内增强全身感染。II型荚膜基因簇的基因组组织已被确定为一个血清型特异性区域2，两侧是区域1和区域3，区域1和区域3包含血清型之间高度同源的转运基因。相比之下，III型荚膜基因簇的组织情况尚不清楚。然而，它们部分是由区域1和区域3中与II型荚膜转运基因无显著核苷酸同源性的基因缺失所定义的。对临床血液分离株（CP9，O4/K54/H5）的同基因TnphoA产生的III型荚膜缺失衍生物进行评估，已鉴定出II型荚膜转运基因kpsDMTE的同源物。对这些基因及其周围区域进行了测序和分析。这些基因的基因组组织与它们的II型对应物明显不同。尽管kps（K54）DMTE在DNA和蛋白质水平上与其II型同源物有显著差异，但phoA融合和计算机辅助分析表明它们的结构和功能相似。推测的蛋白质Kps（K54）M和Kps（K54）T似乎分别是ABC - 2转运蛋白家族的整合膜成分和外周ATP结合成分。推测的Kps（K54）E具有与促进大分子穿过周质的膜融合蛋白家族相似的特征。在荚膜基因簇的一个边界处，鉴定出一个截短的kpsM（kpsM（截短））及其5'非编码调控序列。与完整的kps（K54）M相比，该区域与II型kpsM高度同源。在kpsM（截短）末端下游3'处的53个碱基对是一个与来自天蓝色链霉菌的IS110插入元件中的39碱基对反向重复序列有７５％同源性的序列。Southern分析确定CP9中存在该元件的两个拷贝。这些发现与CP9先前拥有II型荚膜基因并通过IS110介导的水平转移获得III型荚膜基因的假设一致。
