Submitted to: Plasmid Journal
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/21/2004
Publication Date: 3/1/2005
Citation: Davis, R.E., Dally, E.L., Jomantiene, R., Zhao, Y., Roe, B., Lin, S., Shao, J.Y. 2005. Molecular analysis of a cryptic plasmid encoding a putative adhesin and type IV secretion system components in the wall-less plant pathogen Spiroplasma kunkelii. Plasmid. 53:179-190. Interpretive Summary: Spiroplasmas are very small bacteria that lack cell walls, are motile and have a helical cell shape, and cause diseases in plants and insects. They possess very small genomes (relatively small number of genes) and are related to mycoplasmas that cause diseases in animals and humans. The spiroplasma offers a novel model for understanding the spread of antibiotic-resistant bacteria and the emergence of new diseases. Disease-causing bacteria often become resistant to antibiotics and acquire new capabilities for causing diseases. One means by which this occurs is through the exchange of DNA molecules, plasmids, among different bacteria. Spiroplasmas contain plasmids, but none has previously been decoded to determine what antibiotic resistance and disease-related genes they may carry. This paper reports the discovery of a newly recognized spiroplasma plasmid and the genes that are coded by this plasmid. We found that the plasmid is a type that is capable of moving from one bacterial cell to another, spreading the specialized genes that it carries. This information will interest bacteriologists, molecular biologists, epidemiologists, and scientists studying the spread of antibiotic resistance among bacteria that cause diseases in plants, animals, and man.
Technical Abstract: A cryptic plasmid of the wall-less plant pathogenic mollicute, Spiroplasma kunkelii CR2-3X, was cloned and its sequence analyzed. The plasmid, designated pSK146, was 14,615 bp in size, has a nucleotide content of 28 mol% G+C, and contains 18 potential protein coding regions (open reading frames, ORFs), of which five encode proteins that exhibit similarity to virulence-associated proteins involved in cell-to-cell adhesion or conjugal DNA transfer. One ORF encodes a 96 kDa protein, SkARP1, highly similar to SARP1 adhesin protein involved in attachment of S. citri to insect vector gut membrane. Four ORFs encode proteins similar to TraE and Mob in walled bacteria, and to ORFs found in the integrative, conjugative element (ICEF) of Mycoplasma fermentens, respectively. Presence of domains similar to proteins of the Type IV secretion system in pathogenic bacteria suggests that spiroplasma possesses a related secretion system. Plasmid pSK146 also contains two identical oriT regions each containing a nick sequence characteristic of the IncP conjugative plasmid family, as well as palindromic sequences including a 58 bp abutted inverted repeat region (palSK1). Features in pSK146 suggest that the plasmid functions as a mobile genetic element in conjugative transmission of spiroplasma pathogenicity-related genes.