The oppD Gene and Putative Peptidase Genes May Be Required for Virulence in Mycoplasma gallisepticum
Chi-Wen Tseng1, Chien-Ju Chiu1, Anna Kanci1
1Asia-Pacific Centre for Animal Health, Melbourne Veterinary School, Faculty of Veterinary and Agricultural Sciences, The University of Melbourne, Parkville, Victoria, Australia.
Abstract:
Relatively few virulence genes have been identified in pathogenic mycoplasmas, so we used signature-tagged mutagenesis to identify mutants of the avian pathogen Mycoplasma gallisepticum with a reduced capacity to persist in vivo and compared the levels of virulence of selected mutants in experimentally infected chickens. Four mutants had insertions in one of the two incomplete oppABCDF operons, and a further three had insertions in distinct hypothetical genes, two containing peptidase motifs and one containing a member of a gene family. The three hypothetical gene mutants and the two with insertions in oppD1 were used to infect chickens, and all five were shown to have a reduced capacity to induce respiratory tract lesions. One oppD1 mutant and the MGA_1102 and MGA_1079 mutants had a greatly reduced capacity to persist in the respiratory tract and to induce systemic antibody responses against M. gallisepticum The other oppD1 mutant and the MGA_0588 mutant had less capacity than the wild type to persist in the respiratory tract but did elicit systemic antibody responses. Although M. gallisepticum carries two incomplete opp operons, one of which has been acquired by horizontal gene transfer, our results suggest that one of the copies of oppD may be required for full expression of virulence. We have also shown that three hypothetical genes, two of which encode putative peptidases, may be required for full expression of virulence in M. gallisepticum. None of these genes has previously been shown to influence virulence in pathogenic mycoplasmas.
Insights
Researchers identified new virulence factors in Mycoplasma gallisepticum, an avian pathogen. Mutants lacking specific genes showed reduced disease severity and persistence in chickens, highlighting potential targets for controlling this important poultry disease.
Area of Science:
- Microbiology
- Avian Pathogen Research
- Molecular Genetics
Background:
- Limited knowledge exists regarding virulence factors in pathogenic mycoplasmas.
- Mycoplasma gallisepticum is a significant avian pathogen causing respiratory disease.
- Identifying novel virulence genes is crucial for developing control strategies.
Purpose of the Study:
- To identify novel virulence genes in Mycoplasma gallisepticum using signature-tagged mutagenesis.
- To assess the in vivo persistence and pathogenicity of identified mutants in experimentally infected chickens.
- To investigate the role of specific genes, including oppD1 and hypothetical genes, in M. gallisepticum virulence.
Main Methods:
- Signature-tagged mutagenesis was employed to generate random gene knockouts in M. gallisepticum.
- Mutants were screened for reduced in vivo persistence in experimentally infected chickens.
- Virulence levels, respiratory lesion induction, and systemic antibody responses were compared between selected mutants and wild-type strains.
Main Results:
- Four mutants with insertions in oppABCDF operons and three in hypothetical genes showed reduced capacity to induce respiratory lesions.
- One oppD1 mutant and mutants in MGA_1102 and MGA_1079 exhibited significantly reduced persistence and antibody response.
- Other mutants showed reduced respiratory tract persistence but still elicited systemic antibody responses.
Conclusions:
- One copy of oppD may be essential for the full virulence of Mycoplasma gallisepticum.
- Three hypothetical genes, including two encoding putative peptidases, are implicated in M. gallisepticum virulence.
- These findings reveal previously unknown virulence factors in pathogenic mycoplasmas, offering new targets for intervention.
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