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Peritrophic matrix-degrading proteins are dispensable virulence factors in a virulent Melissococcus plutonius strain

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.

Scientific Reports
|April 23, 2021
PubMed

Insights

European foulbrood (EFB) in honey bees is caused by Melissococcus plutonius. While PM-degrading proteins aid bacterial invasion, they are not essential for virulence in highly virulent strains, as shown by knockout mutants.

Area of Science:

  • Apiculture
  • Microbiology
  • Insect Pathology

Background:

  • European foulbrood (EFB) is a significant bacterial disease affecting honey bees.
  • Melissococcus plutonius, the causative agent, displays genetic variability influencing disease virulence.
  • Infected larvae show M. plutonius colonizing the midgut and peritrophic matrix (PM).

Purpose of the Study:

  • To investigate the role of putative PM-degrading proteins in M. plutonius pathogenesis.
  • To determine if these proteins are essential virulence factors in highly virulent strains.

Main Methods:

  • Construction of triple-knockout mutants lacking PM-degrading protein genes (enhancin, chitin-binding domain-containing protein, endo-α-N-acetylgalactosaminidase).
  • Oral infection of bee larvae with wild-type and mutant M. plutonius strains.
  • Observation of bacterial colonization, PM integrity, and larval midgut pathology.

Main Results:

  • In larvae infected with the triple-knockout mutant, M. plutonius remained confined within the PM sac.
  • Midgut epithelial cell degeneration occurred despite the absence of PM-degrading proteins.
  • The triple-knockout mutant caused significant brood mortality (70-80%).

Conclusions:

  • PM-degrading proteins contribute to M. plutonius penetration of the peritrophic matrix.
  • These proteins are not indispensable for virulence in highly virulent M. plutonius strains.
  • Other virulence factors likely play a crucial role in EFB pathogenesis.

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