Genetic analysis and phylogenetic comparison of Black queen cell virus genotypes

Phylogenetic analysis of 22 Black queen cell virus (BQCV) genotypes collected from honeybee colonies in Poland, Austria and Hungary was performed on a partial helicase enzyme coding region (ORF1) and on a partial structural polypeptide coding region (ORF2). While the phylogeny based on the ORF2 region showed – with the exception of one strain from Poland – clustering of the genotypes corresponding to their geographic origin, the ORF1-based tree exhibited a completely different distribution of the Polish strains: three of them clustered within a branch clearly separated from all other central European BQCVs, while four other Polish strains remained well within the central European BQCV genotypes. In order to investigate this discrepancy in more detail, the nearly complete genome sequences of the three differing Polish strains were determined, together with one Hungarian sample. The sequences were aligned to each other and to the reference strain from South-Africa. Comparison of the different genome regions revealed that the 5′-UTR and the intergenic regions of the BQCV genome are highly conserved with longer homologous sections. ORF1 (non-structural protein coding region) was found more variable compared to ORF2 (structural protein coding region). The 5′-proximal third of ORF1 was particularly variable and contained several deletions/insertions. The sudden changes in the similarity levels of BQCV strains in different genomic regions are indicative of preceding recombination events.