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Identification of a native Dichelobacter nodosus plasmid and implications for the evolution of the vap regions

Department of Microbiology, Monash University, Clayton, Victoria, Australia.
Gene (Impact Factor: 2.08). 07/1996; 172(1):111-6. DOI: 10.1016/0378-1119(96)00032-7
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ABSTRACT Studies on the role of various virulence factors of the ovine pathogen, Dichelobacter nodosus, have suffered from the absence of a mechanism for the introduction of DNA into this organism. As an initial step in the development of genetic methods, we have identified and cloned a native 10-kb plasmid, pJIR896, from a clinical isolate. This plasmid was found to be a circular form of vap region 1/3 that is found in the reference strain, A198. However, pJIR896 lacked the duplicated region present in the A198 sequence and instead contained a 1.7-kb putative insertion sequence, IS1253, which shared similarity to a number of unusual IS elements. A model is proposed for the evolution of vap region 1/3 which involves the integration of a plasmid, such as pJIR896, and subsequent rearrangements resulting from the deletion or transposition of IS1253.

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    • "However, it is the nature of the causative bacterial strain, which is decisive for the initiation, and potential severity of an outbreak (Whittington, 1995; Kennan et al., 2010, 2011). A number of virulence factors have been identified in D. nodosus, as e.g. the virulence associated gene regions vap and vrl that are preferentially present in virulent strains and may therefore be indicators of virulence (Katz et al., 1991; Billington et al., 1996). Type IV fimbriae and extracellular proteases are essential for virulence of D. nodosus (Kennan et al., 2001, 2010). "
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    • "Comparative analysis of DNA from virulent and benign strains has led to the identification of a series of genetic elements which integrate into the D. nodosus chromosome. These include the intA [3-7], intB [8], intC [8] and intD elements [9], Tanjung, L. and Cheetham, B.F., unpublished, each of which contains an integrase gene. A fifth element, the virulence-related locus, vrl [6,10,11], lacks an integrase gene. "
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    • "As noted, at least two accessory genetic elements, the vap element of Dichelobacter nodosus , described as a PI, and the recently described Vibrio cholerae PI (Karaolis et al., 1998) encode an Int homologue . The D. nodosus PI may be related to SaPI1, particularly considering the homology between vapE and ORF11 of SaPI1, and is very similar to a plasmid found in some D. nodosus strains (Cheetham and Katz, 1995; Cheetham et al., 1995; Billington et al., 1996), suggesting that the vap element may be mobile. Therefore, SaPI1 and SaPI2 are the first PIs for which mobility has been demonstrated. "
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