Funktionelle Genomanalyse bakterieller Erreger, assoziiert mit der Europäischen Faulbrut von Honigbienen

Abstract

Paenibacillus larvae and Melissococcus plutonius cause American foulbrood (AFB) and European foulbrood (EFB) on honey bees, respectively. Three typical strains of M. plutonius were isolated from a Swiss EFB outbreak. The genomes of one atypical and 13 typical strains were analyzed. For the first time, potential virulence and fitness factors of M. plutonius were detected and, subsequently, analyzed. M. plutonius is able to cause infection and kill the honey bee larvae with the detected and analyzed virulence factors. These virulence factors are bacteriocins, tyrosine decarboxylase, enhancin, a putative PlCBP49-homolog, cell surface proteins, collagenase, one Enterococcal polysaccharide antigen (Epa)-homolog, capsule-forming proteins, proteases, glycoside hydrolases, polysaccharide lyases, and one toxin called Melissotoxin A. Melissotoxin A and one matrix binding protein are plasmid-encoded (pMP19). In former studies it was shown, that typical M. plutonius strains lose their virulence after several cultivation steps. Loss of virulence is putatively associated with the loss of the virulence plasmid (pMP19), which was detected in the genomes of typical strains only. Atypical strains remain highly virulent even without the virulence plasmid. Thus, it is assumed that typical and atypical strains established different virulence mechanisms. Atypical M. plutonius strains putatively consume sugar rich resources in the honey bee larvae’s gut much faster than typical strains. Furthermore, detected surface protein-coding genes of the atypical strain differ from their homologs found in typical strains. Additionally, different grades of virulence were predicted for typical strains based on the presence/absence of genes coding for an endo-alpha-N-acetylgalactosaminidase, tyrosine decarboxylase and the virulence plasmid pMP19. Additionally, it could be shown that three virulence factors were transcribed in vivo during EFB pathogenesis (endo-alpha-N-acetylgalactosaminidase, enhancin and Melissotoxin A). A general EFB infection and -pathogenesis model was proposed. New P. larvae virulence factors were detected by using genome analysis of two strains (belonging to genotype ERIC I and ERIC II, respectively). These virulence factors are bacteriocins, NRPS- and NPRS/PKS-biosynthesis gene cluster, enhancin, hyaluronidase, immune inhibitor A, bacillolysins, toxins, cell surface proteins, and proteases. A general AFB infection model was proposed. Furthermore, the genomes of bacterial honey bee symbionts Lactobacillus kunkeei EFB6 and Fructobacillus sp. EFB-N1 were analyzed.