Identification of Three Novel <i>B. thuringiensis</i> Strains that Produce the Thuricin S Bacteriocin

Abstract

In the present work, three antibacterial substances produced by three Bacillus thuringiensis strains: Bacillus thuringiensis subsp. entomocidus HD9, Bacillus thuringiensis subsp. entomocidus HD110 and Bacillus thuringiensis subsp. tolworthy HD125 were used to study the bacteriocin diversity within Bacillus thuringiensis species. The inhibitory substances produced by these strains were purified to homogeneity by reverse phase high-performance liquid chromatography and were identified as bacteriocins. These molecules were all sensitive to proteinase K, heat-resistant and stable over a wide range of pH (3-10.5). Mass spectrometry ESI-TOF-MS analysis provided the monoisotopic masses of the three newly identified bacteriocins. The N-terminal amino acid sequences were also determined by Edman sequencing and by nanoESI-MS/MS experiments. Interestingly, the three newly identified bacteriocins shared the same molecular mass and the same N-terminal sequence with the anti-Listeria bacteriocin: thuricin S, produced by Bacillus thuringiensis subsp. entomocidus HD198 strain. Thereby, we demonstrated at the biochemical level and for the first time that four different Bacillus thuringiensis strains produce the same bacteriocin.