Identification and Characterization of Spontaneous Deletions within the Sp11-Sp12 Prophage Region of Escherichia coli O157:H7 Sakai
Identification and Characterization of Spontaneous Deletions within the Sp11-Sp12 Prophage Region of Escherichia coli O157:H7 Sakai
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DOI：
10.1128/aem.03682-12
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发表时间：
2013-03-01
影响因子：
4.4
通讯作者：
Dudley, Edward G.
中科院分区：
文献类型：
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作者：
Chen, Chun;Lewis, Carrie R.;Dudley, Edward G.
脯氨酸占肠出血性大肠杆菌基因组的12%，在这种食源性病原体的进化和毒力中发挥重要作用。原噬菌体区域的获得、丢失和重排是导致大肠杆菌菌株间脉冲场凝胶电泳（PFGE）图谱差异的主要原因。coli O157：H7。Sp11和Sp12是大肠杆菌携带的两个串联整合且推定有缺陷的前噬菌体。coli O 157：H7菌株Sakai。在这项研究中，我们确定了3类发生在Sp11-Sp12区域内的缺失，频率约为100%。7.74 x 10（-4）。一个缺失导致Sp11的精确切除，另外两个跨越Sp11和Sp12的交界处。所有缺失导致PFGE观察到的XbaI片段模式发生变化。我们对Sakai的诱导型原噬菌体池进行了测序，但没有鉴定出任何对应于Sp11或Sp12的成熟噬菌体颗粒。含有pchB和psrC的缺失，这是Sp11携带的编码已知或怀疑调节III型分泌的蛋白质的基因，不影响EspA或EspB效应子的分泌水平。将Sp11-Sp12 DNA序列与其它大肠杆菌中相应的序列进行比对。coliO 157：H7和O 55：H7菌株表明，同源重组而不是整合酶介导的切除是这些缺失背后的机制。因此，这项研究提供了一个机制背后的遗传不稳定性，以前观察到的这一基因组区域的E。大肠杆菌O 157：H7。
Prophages make up 12% of the enterohemorrhagic Escherichia coli genome and play prominent roles in the evolution and virulence of this food-borne pathogen. Acquisition and loss of and rearrangements within prophage regions are the primary causes of differences in pulsed-field gel electrophoresis (PFGE) patterns among strains of E. coli O157:H7. Sp11 and Sp12 are two tan-demly integrated and putatively defective prophages carried by E. coli O157:H7 strain Sakai. In this study, we identified 3 classes of deletions that occur within the Sp11-Sp12 region, at a frequency of ca. 7.74 x 10(-4). One deletion resulted in a precise excision of Sp11, and the other two spanned the junction of Sp11 and Sp12. All deletions resulted in shifts in the XbaI fragment pattern observed by PFGE. We sequenced the inducible prophage pool of Sakai but did not identify any mature phage particles corresponding to either Sp11 or Sp12. Deletions containing pchB and psrC, which are Sp11-carried genes encoding proteins known or suspected to regulate type III secretion, did not affect the secretion levels of the EspA or EspB effector. Alignment of the Sp11-Sp12 DNA sequence with its corresponding regions in other E. coli O157:H7 and O55:H7 strains suggested that homologous recombination rather than integrase-mediated excision is the mechanism behind these deletions. Therefore, this study provides a mechanism behind the previously observed genetic instability of this genomic region of E. coli O157:H7.