Analysis of sequences flanking the vap regions of Dichelobacter nodosus: evidence for multiple integration events, a killer system, and a new genetic element

Abstract

Dichelobacter nodosus is the causative agent of ovine footrot. The wap regions of the D. nodosus genome may have arisen by the integration of a genetic element and may have a role in virulence. The virulent D. nodosus strain A198 has multiple copies of the wap regions. In the present study, sequences to the left and right of wap regions 1,2 and 3 of strain A198 were analysed by Southern blotting and DNA sequencing. The results suggest that wap regions 1 and 2 arose by independent integration events into different tRNA genes. The discovery of a second integrase gene (intB), a gene with similarity to bacteriophage repressor proteins (regA), and a gene similar to an ORF from a conjugative transposon (gepA), suggests that a second genetic element either a bacteriophage or a conjugative transposon, is integrated next to wap region 3 in the D. nodosus genome. The arrangement of inti3 and the wap regions in three other virulent strains and one benign strain was determined using using Southern blotting and PCR. One strain, H1215, contained wapF and not wapE, and thus resembles wap region 3, suggesting that wap region 3 also may have arisen by an independent integration event. In all strains, a copy of intS was found next to the wap regions. The wap regions contain two genes, wapA and toxA, with similarity to the hig genes of the killer plasmid Rtsl. Evidence is presented that wapA and toxA have a similar function in D. nodosus.

Microarray Analyses of Xylella fastidiosa Provide Evidence of Coordinated Transcription Control of Laterally Transferred Elements

“…These ORFs display high similarity to a heterodimeric integrase found in association with an insertion element from Helicobacter pylori (Kersulyte et al 2000). The above criteria have been used to characterize GIs from several microorganisms, and the ORF composition of GI 1 is also in accordance with what has been verified in other systems, including 41 hypothetical proteins, six conserved hypothetical proteins, five phage-related factors (including a hemolysin-like enzyme), one lipid A biosynthesis enzyme, one fimbrillin, and the virulenceassociated factor VapE from Dichelobacter nodosus (Bloomfield et al 1997). These latter factors are typically present in pathogenicity islands (PAIs), a subset of GIs that transfer virulence-related genes among microorganisms and are currently viewed as key virulence determinants in many pathogenic (Bjorkholm et al 2001;Dobrindt et al 2002;Dziejman et al 2002;Tauschek et al 2002;Walker and Verma 2002).…”

Sequence Analysis of Insecticidal Genes from Xenorhabdus nematophilus PMFI296

“…The dependence of this bacteria on a nematode host and its growth within an insect may explain how this strain has acquired DNA that is similar to eukaryotic mitochondrial DNA sequences through lateral DNA transfer in this close relationship. It is interesting that the presence of homology to a tRNA gene and the prediction of three tRNA genes near to the potential point of insertion of the toxin genes shows similarity with the other mobile virulence regions in E. coli, Salmonella species, Dichelobacter nodosus, and other bacteria (5,6,19). In these instances, large segments of DNA also insert into tRNA loci, and a number of independent insertion events may have led to the mosaic structure now seen in the genomes of these strains.…”

Comparative Genomic Analysis of Ten Streptococcus pneumoniae Temperate Bacteriophages

“…The proteins encoded in this position showed 96.2% amino acid identity among them, and their consensus sequence showed a 29% amino acid identity (E value, 10 Ϫ34 ; identity, 104/353 bases) with the virulence-associated protein E (VapE) of Dichelobacter nodosus, in which this domain was originally identified (36). vapE is part of the vap regions of D. nodosus that have been associated with virulence (8). The mechanism of VapE in the virulence of D. nodosus has not been determined yet, but the presence of an integrase gene, showing similarities to integrase genes of Shigella flexneri phage Sf6 and coliphages P4 and R7 located immediately upstream of vapE, suggested a role for bacteriophages in the evolution and transfer of these bacterial virulence determinants (13).…”