G Whittle

Publications (3)7.64 Total impact

• Article: Identification and characterization of a native Dichelobacter nodosus plasmid, pDN1.

  G Whittle, M E Katz, E H Clayton, B F Cheetham
  [show abstract] [hide abstract]
  ABSTRACT: The gram-negative anaerobe Dichelobacter nodosus is the primary causative agent of ovine footrot, a mixed bacterial infection of the hoof. We report here the characterization of a novel native plasmid, pDN1, from D. nodosus. Sequence analysis has revealed that pDN1 has a high degree of similarity to broad-host-range plasmids belonging, or related, to Escherichia coli incompatibility group Q. However, in contrast to these plasmids, pDN1 encodes no antibiotic resistance determinants, lacks genes E and F, and hence is smaller than all previously reported IncQ plasmids. In addition, pDN1 belongs to a different incompatibility group than the IncQ plasmids to which it is related. However, pDN1 does contain the replication and mobilization genes that are responsible for the extremely broad host range characteristic of IncQ plasmids, and derivatives of pDN1 replicate in E. coli. In addition, the mobilization determinants of pDN1 are functional, since derivatives of pDN1 are mobilized by the IncPalpha plasmid RP4 in E. coli.
  Plasmid 06/2000; 43(3):230-4. · 1.52 Impact Factor
• Article: The site-specific integration of genetic elements may modulate thermostable protease production, a virulence factor in Dichelobacter nodosus, the causative agent of ovine footrot.

  G Whittle, G A Bloomfield, M E Katz, B F Cheetham
  [show abstract] [hide abstract]
  ABSTRACT: The gram-negative anaerobe Dichelobacter nodosus is the causative agent of footrot in sheep. The authors have previously characterized two genetic elements, the intA (vap) and intB elements, which integrate into the genome of D. nodosus. In the virulent strain A198 there are two copies of the intA element. One copy is integrated into the 3' end of the tRNA-serGCU gene, close to the aspartokinase (askA) gene, and the second copy is integrated into the 3' end of the tRNA-serGGA gene, next to the polynucleotide phosphorylase (pnpA) gene. In this study, a new genetic element was identified in the benign strain C305, the intC element, integrated into the 3' end of the tRNA-serGCU gene, next to askA. The intC element was found in most D. nodosus strains, both benign and virulent, which were examined, and was integrated into tRNA-serGCU in most strains. Between the askA and tRNA-serGCU genes, a gene (designated glpA), was identified whose predicted protein product has very high amino acid identity with RsmA from the plant pathogen Erwinia carotovora. RsmA acts as a global repressor of pathogenicity in E. carotovora, by repressing the production of extracellular enzymes. In virulent strains of D. nodosus the intA element was found to be integrated next to pnpA, and either the intA or intC element was integrated next to glpA. By contrast, all but one of the benign strains had intB at one or both of these two positions, and the one exception had neither intA, intB nor intC at one position. The loss of the intC element from the virulent strain 1311 resulted in loss of thermostable protease activity, a virulence factor in D. nodosus. A model for virulence is proposed whereby integration of the intA and intC genetic elements modulates virulence by altering the expression of glpA, pnpA, tRNA-serGCU and tRNA-serGGA.
  Microbiology 11/1999; 145 ( Pt 10):2845-55. · 3.06 Impact Factor
• Source

  Available from: sgmjournals.org

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

  G A Bloomfield, G Whittle, M B McDonagh, M E Katz, B F Cheetham
  [show abstract] [hide abstract]
  ABSTRACT: Dichelobacter nodosus is the causative agent of ovine footrot. The vap 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 vap regions. In the present study, sequences to the left and right of vap regions 1, 2 and 3 of strain A198 were analysed by Southern blotting and DNa sequencing. The results suggest that vap regions 1 and 2 rose 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 vap region 3 in the D. nodosus genome. The arrangement of intB and the vap regions in three other virulent strains and one benign strain was determined using using Southern blotting and PCR. One strain, H1215, contained vapE' and not vapE, and thus resembles vap region 3, suggesting that vap region 3 also may have arisen by an independent integration event. In all strains, a copy of intB was found next to the vap regions. The vap regions contain two genes, vapA and toxA, with similarity to the hig genes of the killer plasmid Rts1. Evidence is presented that vapA and toxA have a similar function in D. nodosus.
  Microbiology 03/1997; 143 ( Pt 2):553-62. · 3.06 Impact Factor