Preparative high-performance liquid chromatographic separation and analysis of the Maltacine complex – a family of cyclic peptide antibiotics from Bacillus subtilis

Purification of secondary metabolites from fermentation broths can be a challenging task both due to the complexity of the medium, inherently unstable molecular structures or by the action of enzymes present in the fermentation broth leading to poor isolation yield and loss of antibiotic activity. A combination of different purification techniques has usually been used to arrive at acceptable purities for characterisation of the target molecules. Due to rapid decay of antimicrobial activity a rapid preparative high-performance liquid chromatography (HPLC) method was developed that provided separation and resolution of a family of 18 closely related cyclic peptides within 110 min with minimal loss of activity. Characterisation of the peptides with LC–MS, UV/IR spectroscopy and amino acid analysis disclosed 20 different peptides with cyclic structures (lactones) with molecular weights between 1447.7 and 1519.8 Da. No peptide antibiotics with identical molecular weights have previously been reported in the literature, which lead us to conclude that this peptide complex has not been discovered before. We have named them Maltacines.