Elucidation of sevadicin, a novel non‐ribosomal peptide secondary metabolite produced by the honey bee pathogenic bacterium P aenibacillus larvae

Summary A merican foulbrood ( AFB ) caused by the bee pathogenic bacterium P aenibacillus larvae is the most devastating bacterial disease of honey bees worldwide. From AFB ‐dead larvae, pure cultures of P . larvae can normally be cultivated indicating that P . larvae is able to defend its niche against all other bacteria present. Recently, comparative genome analysis within the species P . larvae suggested the presence of gene clusters coding for multi‐enzyme complexes, such as non‐ribosomal peptide synthetases ( NRPS s). The products of these enzyme complexes are known to have a wide range of biological activities including antibacterial activities. We here present our results on antibacterial activity exhibited by vegetative P . larvae and the identification and analysis of a novel antibacterially active P . larvae tripeptide (called sevadicin; S ev) produced by a NRPS encoded by a gene cluster found in the genome of P . larvae . Identification of S ev was ultimately achieved by comparing the secretome of wild‐type P . larvae with knockout mutants of P . larvae lacking production of S ev. Subsequent mass spectrometric studies, enantiomer analytics and chemical synthesis revealed the sequence and configuration of the tripeptide, D ‐Phe‐ D ‐ ALa ‐Trp, which was shown to have antibacterial activity. The relevance of our findings is discussed in respect to host–pathogen interactions.