Characterization of VPI pathogenicity island and CTXφ prophage in environmental strains of Vibrio cholerae
Characterization of VPI pathogenicity island and CTXφ prophage in environmental strains of Vibrio cholerae
复制标题
DOI：
10.1128/jb.183.16.4737-4746.2001
复制
发表时间：
2001-08-01
影响因子：
3.2
通讯作者：
Berg, DE
中科院分区：
文献类型：
--
作者：
Mukhopadhyay, AK;Chakraborty, S;Berg, DE
采用PCR和测序技术对印度加尔各答霍乱弧菌环境分离株的8种随机扩增多态性DNA （RAPD）指纹型进行了研究，这些菌株含有毒素协同调节菌毛或霍乱毒素基因，但不含流行菌株的O1或O139抗原。我们发现每个分离株都含有VPI致病性岛的一种变体形式。区别特征包括：(i) tcpF的四个新等位基因（编码分泌的毒力蛋白，其确切功能尚不清楚），在蛋白质水平上与标准tcpF彼此差异20%至70%；（ii）一个新的毒力调控基因（toxT）等位基因，在其5‘半部分与标准toxT有36%的差异（在蛋白质水平上），在其3’半部分与标准toxT几乎相同；（iii）一个新的tcpA （pilin）基因；（iv） WT上游调控序列的四种变体形式。还发现了is903相关元件和功能未知基因在VPI位点的转位。霍乱毒素（ctx）基因在两种RAPD类型的分离株中发现，每种情况下都嵌入ctx phi样噬菌体中。在其他两种RAPD类型中，推测仅含有推定的抑制基因、复制基因和整合基因的片段也存在。还鉴定了新的可能的前噬菌体抑制基因和复制基因。我们的研究结果表明，在一些非流行霍乱弧菌菌株中发现的毒力相关基因簇存在显著的遗传多样性，表明其中一些基因有助于自然界的适应性，并强调了菌株间基因交换在该物种进化中的潜在重要性。
Environmental isolates of Vibrio cholerae of eight randomly amplified polymorphic DNA (RAPD) fingerprint types from Calcutta, India, that were unusual in containing toxin-coregulated pilus or cholera toxin genes but not O1 or O139 antigens of epidemic strains were studied by PCR and sequencing to gain insights into V. cholerae evolution. We found that each isolate contained a variant form of the VPI pathogenicity island. Distinguishing features included (i) four new alleles of tcpF (which encodes secreted virulence protein; its exact function is unknown), 20 to 70% divergent (at the protein level) from each other and canonical tcpF; (ii) a new allele of toxT (virulence regulatory gene), 36% divergent (at the protein level) in its 5' half and nearly identical in its 3' half to canonical toxT, (iii) a new tcpA (pilin) gene; and (iv) four variant forms of a regulatory sequence upstream of WT. Also found were transpositions of an IS903-related element and function-un known genes to sites in VPI. Cholera toxin (ctx) genes were found in isolates of two RAPD types, in each case embedded in CTX phi -like prophages. Fragments that are inferred to contain only putative repressor, replication, and integration genes were present in two other RAPD types. New possible prophage repressor and replication genes were also identified. Our results show marked genetic diversity in the virulence-associated gene clusters found in some nonepidemic V. cholerae strains, suggest that some of these genes contribute to fitness in nature, and emphasize the potential importance of interstrain gene exchange in the evolution of this species.