Amylocyclicin, a Novel Circular Bacteriocin Produced by Bacillus amyloliquefaciens FZB42

Bacillus amyloliquefaciens FZB42 is a Gram-positive plant growth-promoting bacterium with an impressive capacity to synthesize nonribosomal secondary metabolites with antimicrobial activity. Here we report on a novel circular bacteriocin which is ribosomally synthesized by FZB42. The compound displayed high antibacterial activity against closely related Gram-positive bacteria. Transposon mutagenesis and subsequent site-specific mutagenesis combined with matrix-assisted laser desorption ionization-time of flight mass spectroscopy revealed that a cluster of six genes covering 4,490 bp was responsible for the production, modification, and export of and immunity to an antibacterial compound, here designated amylocyclicin, with a molecular mass of 6,381 Da. Peptide sequencing of the fragments obtained after tryptic digestion of the purified peptide revealed posttranslational cleavage of an N-terminal extension and head-to-tail circularization of the novel bacteriocin. Homology to other putative circular bacteriocins in related bacteria let us assume that this type of peptide is widespread among the Bacillus/Paenibacillus taxon.