Comparative Genomics and Description of Putative Virulence Factors of , the Causative Agent of European Foulbrood Disease in Honey Bees.

In Europe, approximately 84% of cultivated crop species depend on insect pollinators, mainly bees. (the Western honey bee) is the most important commercial pollinator worldwide. The Gram-positive bacterium is the causative agent of European foulbrood (EFB), a global honey bee brood disease. In order to detect putative virulence factors, we sequenced and analyzed the genomes of 14 strains, including two reference isolates. The isolates do not show a high diversity in genome size or number of predicted protein-encoding genes, ranging from 2.021 to 2.101 Mbp and 1589 to 1686, respectively. Comparative genomics detected genes that might play a role in EFB pathogenesis and ultimately in the death of the honey bee larvae. These include bacteriocins, bacteria cell surface- and host cell adhesion-associated proteins, an enterococcal polysaccharide antigen, an epsilon toxin, proteolytic enzymes, and capsule-associated proteins. In vivo expression of three putative virulence factors (endo-alpha--acetylgalactosaminidase, enhancin and epsilon toxin) was verified using naturally infected larvae. With our strain collection, we show for the first time that genomic differences exist between non-virulent and virulent typical strains, as well as a highly virulent atypical strain, that may contribute to the virulence of . Finally, we also detected a high number of conserved pseudogenes (75 to 156) per genome, which indicates genomic reduction during evolutionary host adaptation.