Associated Tissue Bank of Faculty of Medicine, P. J. Safárik University and L. Pasteur University Hospital, Trieda SNP1, 041 66 Kosice, Slovakia.
Curr Microbiol. 2013 Oct;67(4):437-41. doi: 10.1007/s00284-013-0386-6. Epub 2013 May 17.
The complete nucleotide sequence of a small cryptic plasmid pKST21 from Escherichia coli was determined. This plasmid is 1,460 bp long with an overall GC content of 51 %. Based on sequence analysis, the presence of two segments with different average GC density was observed. The segment with higher GC content revealed 98-90 % similarity to several small plasmids of E. coli and to pCR1 from Gram-positive Corynebacterium renale. Plasmid pKST21 possesses two conversely oriented open reading frames encoding proteins with a high degree of amino acid identity to Rep proteins involved in replication. ORF1 encodes replication protein similar to RepA protein of Bartonella tribocorum or Bacillus cereus plasmids or to the putative plasmid Rep protein from ecologically close Selenomonas ruminantium. ORF2 similarly encodes a replication protein, which shares 97 % homology with Rep protein from C. renale. Genetic diversity observed in plasmid pKST21 indicates a mosaic structure of the plasmid with different segments acquired from different sources. Deletion analysis showed that both fragments carrying the repA and repB genes are necessary for the replication of pKST21 in E. coli. The presence of plasmid with the same gene composition was revealed in 14 % of tested E. coli isolates from the rumen of sheep. All these strains produced identical ERIC-PCR profiles indicating isogenic origin of the strain and lack of horizontal gene transfer of pKST21 plasmid.
已确定大肠杆菌小型隐秘质粒 pKST21 的完整核苷酸序列。该质粒长 1460bp，总 GC 含量为 51%。基于序列分析，观察到存在两个具有不同平均 GC 密度的片段。GC 含量较高的片段与大肠杆菌的几个小型质粒和革兰阳性棒状杆菌的 pCR1 具有 98-90%的相似性。质粒 pKST21 包含两个相反取向的开放阅读框，编码与复制相关的 Rep 蛋白具有高度氨基酸同一性的蛋白质。ORF1 编码复制蛋白，与 Bartonella tribocorum 或 Bacillus cereus 质粒的 RepA 蛋白或生态上接近的 Selenomonas ruminantium 的假定质粒 Rep 蛋白相似。ORF2 同样编码复制蛋白，与 C. renale 的 Rep 蛋白具有 97%的同源性。质粒 pKST21 中观察到的遗传多样性表明该质粒具有不同来源的不同片段的镶嵌结构。缺失分析表明，携带 repA 和 repB 基因的两个片段对于 pKST21 在大肠杆菌中的复制都是必需的。在来自绵羊瘤胃的 14%测试大肠杆菌分离株中发现了具有相同基因组成的质粒。所有这些菌株产生相同的 ERIC-PCR 图谱，表明该菌株具有同源性，并且缺乏 pKST21 质粒的水平基因转移。
