American Foulbrood of Honey Bees: Analysis of the Molecular Pathogenesis

• Applicant: Professorin Dr. Elke Genersch
• Subject Area: Veterinary Medical Science
• Term: from 2008 to 2016
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 77330324

Paenibacillus larvae (P. larvae) is the etiological agent of American Foulbrood (AFB), a severe brood disease of the Western honey bee Apis mellifera. Larvae become infected through ingesting larval diet contaminated with spores of the Gram-positive bacterium P. larvae. Only first instar larvae (up to 36 hours after egg hatching) are susceptible to infection. Infected larvae die throughout the entire infection process but latest at the stage of engorged larvae. They are then decomposed by P. larvae to a ropy mass, which is a characteristic sign for AFB. Although AFB is a highly relevant bee disease, only few studies are available on P. larvae on a molecular level. Especially pathogenicity and virulence associated factors of this bacterium remain largely elusive.Recently, we could show that the species P. larvae comprises four genotypes (ERIC I to IV) which differ in virulence. We hypothesized that these differences in virulence are due to differences in the presence and/or expression of virulence genes/factors. During the first phase of this project we compared the genomes and proteomes of the P. larvae genotypes and we were indeed able to identify several virulence associated genes/proteins which differ between the genotypes. For one of these factors, the ERIC II-specific S-layer protein SplA, we were already able to show that it plays an important role in P. larvae ERIC II virulence. During the second phase of this project we want to continue with our work by functionally characterizing not only SplA but also of the other putative and interesting virulence factors identified in the first phase (e.g., toxins Plx1 and Plx2, immune inhibitor InhA, enhancin, non-ribosomal peptides and polyketides, chitin binding and degrading protein CBP49). We will use the molecular tools developed in the first phase of the project, i.e. strategies to knockout and to express genes in P. larvae. We will also develop suitable functional assays for the virulence factors to be analyzed. These studies will help to identify and describe molecular pathomechanisms involved in the infection process and responsible for the differences in virulence. To obtain a comprehensive understanding of the pathogen-host-interactions we will perform comparative transcriptome analysis to study the differential immune response larvae might mount against the different P. larvae genotypes. One focus of our studies will be the impact of the S-layer protein on the immune response of larvae and the impact of the immune response on the infection process. So far our comparative omics studies have been quite successful. We, therefore, expect that also the third omics level will further our understanding of AFB pathogenesis.

• DFG Programme: Research Grants