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Published on: February 23, 2014
Different impacts of pMP19 on the virulence of Melissococcus plutonius strains with different genetic backgrounds
Keiko Nakamura1, Kayo Okumura2, Mariko Harada1
1Research and Business Promotion Division, Research Institute for Animal Science in Biochemistry and Toxicology, Sagamihara, Kanagawa, 252-0132, Japan.
Abstract:
Virulence factors responsible for bacterial pathogenicity are often encoded by plasmids. In Melissococcus plutonius, the causative agent of European foulbrood of honey bees, a putative virulence plasmid (pMP19) possessing mtxA, which encodes a putative insecticidal toxin, was found by comparative genome analyses. However, as the role of pMP19 in the pathogenesis of European foulbrood remains to be elucidated, we generated pMP19 cured-M. plutonius from representative strains of the three genetically distinct groups (CC3, CC12 and CC13) and compared their virulence against Apis mellifera larvae using our in vitro infection model. Under the conditions tested, the loss of pMP19 abrogated the pathogenicity in CC3 strains, and > 94% of pMP19-cured CC3 strain-infected larvae became adult bees, suggesting that pMP19 is a virulence determinant of CC3 strains. However, introduction of mtxA on its own did not increase the virulence of pMP19-cured strains. In contrast to CC3 strains, the representative CC12 strain remained virulent even in the absence of pMP19, whereas the representative CC13 strain was avirulent even in the presence of the plasmid. Thus, pMP19 plays a role in the virulence of M. plutonius; however, its impact on the virulence varies among strains with different genetic backgrounds.
Insights
The plasmid pMP19 is crucial for the virulence of Melissococcus plutonius in honey bee larvae, particularly in CC3 strains. Its impact varies across different genetic groups of this important bee pathogen.
Area of Science:
- Bacteriology
- Apiculture
- Molecular Biology
Background:
- Bacterial virulence factors are often plasmid-encoded.
- Melissococcus plutonius causes European foulbrood in honey bees.
- A putative virulence plasmid, pMP19, containing mtxA was previously identified in M. plutonius.
Purpose of the Study:
- To investigate the role of the pMP19 plasmid in the pathogenicity of Melissococcus plutonius.
- To determine if the mtxA gene alone contributes to virulence.
- To assess the strain-specific impact of pMP19 on European foulbrood pathogenesis.
Main Methods:
- Generation of pMP19-cured M. plutonius strains from CC3, CC12, and CC13 genetic groups.
- In vitro comparison of the virulence of cured and wild-type strains against Apis mellifera larvae.
- Assessment of pathogenicity following the introduction of mtxA into cured strains.
Main Results:
- Loss of pMP19 abrogated pathogenicity in CC3 strains, with most larvae surviving.
- Introduction of mtxA alone did not restore virulence in cured CC3 strains.
- CC12 strains remained virulent without pMP19, while CC13 strains were avirulent even with pMP19.
Conclusions:
- pMP19 is a key virulence determinant for M. plutonius CC3 strains.
- The contribution of pMP19 to M. plutonius virulence is strain-dependent and influenced by genetic background.
- mtxA alone is not sufficient to confer virulence, suggesting other factors on pMP19 are involved.
