CONICET | Buscador de Institutos y Recursos Humanos

Species of Bacillus and Brevibacillus associated with honey bees are interesting sources of bioactive compounds with potentialuses beyond the field of apiculture. Most Bacillus species and related genera produce a broad range of antimicrobial compounds,with activity against bacteria and fungi that include peptides, lipopeptides, bacteriocins, and bacteriocin-like inhibitorysubstances. By using biological tools, we evaluated the antagonistic activity of 34 bacterial strains against Paenibacilluslarvae and Ascosphaera apis, the causal agents of American Foulbrood and Chalkbrood diseases of honey bee larvae, respectively.Data reveal that the antagonistic response was strain-specific, species-specific, and also medium-dependent. By usingmolecular tools, we investigated the distribution of antimicrobial peptide genes in the antagonist strains. The presence ofhomologous sequences to nine genes encoding for the synthesis of the antimicrobial peptides bacillomycin L (bmyB), fengycin(fenD), bacilysin (bacA), subtilin (spaS), iturin A (ituD, lpa-14; ituC), and surfactin (sfp; srfAA) was assayed by PCR. The distributionand frequency of these genes within the bacterial antagonists were also variable and strain-dependent, being themost common surfactins (srfAA¼ 44% and lpa-14¼ 38%), iturins (ituD¼ 47%), and bacilysin (bacA¼ 32%). Moreover, a positivecorrelation between presence of antimicrobial peptide genes and antagonism was found taking into account that 85%of the antagonists had at least one of the antimicrobial peptide genes. We also identified those antagonists active against differentP. larvae genotypes. To our knowledge, this is the first study of the association between the presence of homologoussequences of antimicrobial peptide genes and antagonism against P. larvae and A. apis strains.