Biochemical and genetic characterisation of cerein 7 and cerein 8, two novel bacteriocins produced by Bacillus cereus Bc7, isolated from a soil sample

Many bacteria produce different antibiotic compounds that provide them with adaptative advantage against competitors in natural environments. Some of these compounds can be used in controlling natural populations by acting on targets different than those blocked by most of the currently used antibiotics.;On the other hand, the use of these compounds as food preservatives increases their economic interest. On this context, several soil isolates belonging to the genus Bacillus were screened for bactericidal activity and two of them were found to produce antimicrobial substances: Bacillus megaterium Bm38 and Bacillus cereus Bc7; Bc7 showed the strongest inhibitory activity. The aim of the present work is to understand the biochemical and genetic determinants involved in the production of Bc7 antimicrobial activity. The results of this study will increase the tools for the fight against infectious diseases.;Bacillus cereus Bc7 produces heat stable antibiotic peptides (bacteriocins), active against a large number of Gram-positive bacteria (including Listeria species) but inactive against Gram-negatives. Purification to homogeneity by hydrophobic-interaction, cation-exchange, and reverse-phase liquid chromatography (FPLC) revealed that Bacillus cereus Bc7 produces two bacteriocins, cerein-7 and cerein-8 that can be distinguished by their N-terminal amino acid sequences (N-Gly-Trp-Gly-Asp-Val-Leu for cerein-7 and N-Gly-Trp-Trp-Asn-Ser-Trp-Gly-Lys for cerein-8). Their mode of action is bactericidal and, in some cases, bacteriolytic, suggesting a "two steps" mechanism in which a primary effect disrupts membrane integrity causing cell death in many bacilli whereas, in some cocci, a secondary effect triggers autolytic processes in susceptible bacteria.;The gene encoding cerein-8 was sequenced, its primary translation product was a 74 amino-acids peptide containing a leader sequence of the double-glycine type. This leader peptide is proteolytically processed to produce the mature cerein-8 of 56 amino-acids, with a theoretical molecular weight of 4.893. The deduced sequence of the leader peptide of 18 amino-acids indicates that it is related to sec-independent N-terminal extensions.