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: 2.14).
07/1996; 172(1):111-6. DOI: 10.1016/0378-1119(96)00032-7
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.
Available from: Peter Kuhnert
- "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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ABSTRACT: Dichelobacter nodosus, the etiological agent of ovine footrot, exists both as virulent and as benign strains, which differ in virulence mainly due to subtle differences in the three subtilisin-like proteases AprV2, AprV5 and BprV found in virulent, and AprB2, AprB5 and BprB in benign strains of D. nodosus. Our objective was a molecular genetic epidemiological analysis of the genes of these proteases by direct sequence analysis from clinical material of sheep from herds with and without history of footrot from 4 different European countries. The data reveal the two proteases known as virulent AprV2 and benign AprB2 to correlate fully to the clinical status of the individuals or the footrot history of the herd. In samples taken from affected herds, the aprV2 gene was found as a single allele whereas in samples from unaffected herds several alleles with minor modifications of the aprB2 gene were detected. The different alleles of aprB2 were related to the herds. The aprV5 and aprB5 genes were found in the form of several alleles scattered without distinction between affected and non-affected herds. However, all different alleles of aprV5 and aprB5 encode the same amino acid sequences, indicating the existence of a single protease isoenzyme 5 in both benign and virulent strains. The genes of the basic proteases BprV and BprB also exist as various alleles. However, differences found in samples from affected versus non-affected herds do not reflect the currently known epitopes that are attributed to differences in biochemical activity. The data of the study confirm the prominent role of AprV2 in the virulence of D. nodosus and shed a new light on the presence of the other protease genes and their allelic variants in clinical samples.
Available from: Julian I Rood
- "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 , intC  and intD elements , 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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ABSTRACT: The Gram-negative anaerobic pathogen Dichelobacter nodosus carries several genetic elements that integrate into the chromosome. These include the intA, intB, intC and intD elements, which integrate adjacent to csrA and pnpA, two putative global regulators of virulence and the virulence-related locus, vrl, which integrates into ssrA. Treatment of D. nodosus strains with ultraviolet light resulted in the isolation of DinoHI, a member of the Siphoviridae and the first bacteriophage to be identified in D. nodosus. Part of the DinoHI genome containing the packaging site is found in all D. nodosus strains tested and is located at the end of the vrl, suggesting a role for DinoHI in the transfer of the vrl by transduction. Like the intB element, the DinoHI genome contains a copy of regA which has similarity to the repressors of lambdoid bacteriophages, suggesting that the maintenance of DinoHI and the intB element may be co-ordinately controlled.
Available from: Jodi A Lindsay
- "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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ABSTRACT: Tst, the gene for toxic shock syndrome toxin-1 (TSST-1), is part of a 15.2 kb genetic element in Staphylococcus aureus that is absent in TSST-1-negative strains. The prototype, in RN4282, is flanked by a 17 nucleotide direct repeat and contains genes for a second possible superantigen toxin, a Dichelobacter nodosus VapE homologue and a putative integrase. It is readily transferred to a recA− recipient, and it always inserts into a unique chromosomal copy of the 17 nucleotide sequence in the same orientation. It is excised and circularized by staphylococcal phages φ13 and 80α and replicates during the growth of the latter, which transduces it at very high frequency. Because of its site and orientation specificity and because it lacks other identifiable phage-like genes, we consider it to be a pathogenicity island (PI) rather than a transposon or a defective phage. The tst element in RN4282, near tyrB, is designated SaPI1. That in RN3984 in the trp region is only partially homologous to SaPI1 and is excised by phage 80 but not by 80α. It is designated SaPI2. These PIs are the first in any Gram-positive species and the first for which mobility has been demonstrated. Their mobility may be responsible for the spread of TSST-1 production among S. aureus strains.
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