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Sequence comparisons of plasmids pBJS-O of Spiroplasma citri and pSKU146 of S. kunkelii: implications for plasmid

Bharat D Joshi1, Michael Berg, Janet Rogers

  • 1Department of Biochemistry and Molecular Biology, Oklahoma State University, 246 NRC, Stillwater, OK 74078, USA. bharat@biochem.okstate.edu

BMC Genomics
|December 13, 2005
PubMed
Abstract

Insights

Spiroplasma plasmids pBJS-O and pSKU146 show divergence due to recombination events. Spiroplasma citri BR3-3X harbors a novel plasmid, pBJS, encoding the adhesin SARP1, suggesting a role in conjugation.

Area of Science:

  • Microbiology
  • Genetics
  • Plant Pathology

Background:

  • Spiroplasma citri and S. kunkelii cause significant plant diseases.
  • S. citri BR3-3X has plasmid pBJS-O encoding SARP1, important for vector adhesion.
  • S. kunkelii CR2-3X has plasmid pSKU146 encoding homolog Sk-ARP1.

Purpose of the Study:

  • To investigate the relationship between S. citri and S. kunkelii plasmids.
  • To characterize the novel plasmid pBJS from S. citri BR3-3X.
  • To understand the genetic basis of Spiroplasma pathogenicity and vector interaction.

Main Methods:

  • Nucleotide sequencing of pBJS-O and comparison with pSKU146 and other plasmids.
  • Bioinformatic analysis of open reading frames (ORFs) and gene homologs.
  • Southern blot hybridization to assess sequence conservation across Spiroplasma species.
  • Identification of chromosomal genes, including arp2.

Main Results:

  • pBJS-O is 13,374 bp and contains nine putative ORFs, including arp1.
  • Several pBJS-O ORFs have homologs in pSKU146, but flanking regions differ significantly.
  • pBJS-O lacks the conserved oriT region found in IncP plasmids; pBJS-T shows a deletion compared to pBJS-O.
  • Limited sequence conservation of pBJS-O and arp genes was observed across the Spiroplasma genus.
  • An additional homolog, arp2 (encoding SARP2), was identified on the S. citri BR3-3X chromosome.

Conclusions:

  • pBJS represents a novel S. citri plasmid, not fitting known incompatibility groups.
  • Recombination events likely contributed to plasmid divergence between S. citri and S. kunkelii.
  • Slight plasmid divergence occurred during the derivation of S. citri BR3-T from BR3-3X.
  • pBJS-O encodes SARP1, and the presence of traE and mob suggests a role in spiroplasmal conjugation.

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