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Evidence for plasmid-encoded virulence factors in the phytopathogenic bacterium Clavibacter michiganensis subsp.
D Meletzus1, A Bermphol, J Dreier
1Fakultät für Biologie, Gentechnologie/Mikrobiologie, Universität Bielefeld, Germany.
Abstract:
The tomato pathogen Clavibacter michiganensis subsp. michiganensis NCPPB382, which causes bacterial wilt, harbors two plasmids pCM1 (27.5 kb) and pCM2 (72 kb). After curing of the plasmids, bacterial derivatives were still proficient in the ability to colonize the host plant and in the production of exopolysaccharides but exhibited a reduced virulence. When one of the two plasmids is lost, there is a significant delay in the development of wilting symptoms after infection and a plasmid-free derivative is not able to induce disease symptoms. By cloning of restriction fragments of both plasmids in the plasmid-free strain CMM100, two DNA fragments which restored the virulent phenotype were identified. Further analysis suggested that a fragment of plasmid pCM1 encodes an endocellulase which is involved in the expression of the pathogenic phenotype.
Insights
The tomato pathogen Clavibacter michiganensis subsp. michiganensis requires specific plasmids for full virulence. Loss of these plasmids significantly reduces or eliminates its ability to cause bacterial wilt disease.
Area of Science:
- Plant Pathology
- Bacteriology
- Molecular Biology
Background:
- Clavibacter michiganensis subsp. michiganensis (Cmm) causes bacterial wilt in tomatoes.
- Cmm NCPPB382 harbors two plasmids, pCM1 and pCM2, which may influence virulence.
Purpose of the Study:
- To investigate the role of plasmids pCM1 and pCM2 in the virulence of Cmm NCPPB382.
- To identify specific genes or DNA fragments on the plasmids responsible for pathogenicity.
Main Methods:
- Plasmid curing experiments to generate plasmid-free derivatives.
- Virulence assays on tomato plants to assess pathogenicity.
- Cloning of plasmid restriction fragments into a plasmid-free strain to restore virulence.
Main Results:
- Plasmid-free Cmm derivatives showed reduced virulence, delayed wilting, and inability to induce disease.
- Two DNA fragments, one from pCM1 and another, were identified that restored the virulent phenotype.
- A fragment from pCM1 encodes an endocellulase implicated in the pathogenic phenotype.
Conclusions:
- Plasmids are essential for the full virulence of Cmm NCPPB382 in tomato.
- An endocellulase encoded by a pCM1 fragment plays a key role in Cmm pathogenicity.
- Understanding these plasmid-borne factors can inform strategies for managing bacterial wilt.