Lichenicidin is a class II two-component lantibiotic produced by Bacillus licheniformis. It is composed of the two peptides Bliα and Bliβ, which act synergistically against various Gram-positive bacteria. The lichenicidin gene cluster was successfully expressed in Escherichia coli, thus constituting the first report to our knowledge of a full reconstitution of a lantibiotic biosynthetic pathway in vivo by a Gram-negative host. This system was further exploited to characterize and assign the function of proteins encoded in the biosynthetic gene cluster in the maturation of lichenicidin peptides. Moreover, a trans complementation system was developed for expression of Bliα and Bliβ variants in vivo. This contribution will spur future studies in the heterologous expression and engineering of lantibiotics.

Research on ribosomally synthesized and posttranslationally modified peptides (RiPPs) has led to an increasing understanding of biosynthetic mechanisms, mostly drawn from bacterial examples. In contrast, reports on RiPPs from fungal producers, apart from the amanitins and phalloidins, are still scarce. The fungal cyclopeptide omphalotin A carries multiple N-methylations on the peptide backbone, a modification previously known only from nonribosomal peptides. Mining the genome of the omphalotin-producing fungus for a precursor peptide led to the identification of two biosynthesis genes, one encoding a methyltransferase OphMA that catalyzes the automethylation of its C-terminus, which is then released and cyclized by the protease OphP. Our findings suggest a novel biosynthesis mechanism for a RiPP in which a modifying enzyme bears its own precursor peptide.

The spore-forming bacterium Paenibacillus larvae is the causative agent of American Foulbrood (AFB), a fatal disease of honey bees that occurs worldwide. Previously, we identified a complex hybrid nonribosomal peptide/polyketide synthesis (NRPS/PKS) gene cluster in the genome of P. larvae. Herein, we present the isolation and structure elucidation of the antibacterial and antifungal products of this gene cluster, termed paenilamicins. The unique structures of the paenilamicins give deep insight into the underlying complex hybrid NRPS/PKS biosynthetic machinery. Bee larval co-infection assays reveal that the paenilamicins are employed by P. larvae in fighting ecological niche competitors and are not directly involved in killing the bee larvae. Their antibacterial and antifungal activities qualify the paenilamicins as attractive candidates for drug development.

The E. coli siderophore enterobactin, one of the strongest Fe(III) chelators known to date, is also capable of binding Si(IV) under physiological conditions. We report on the synthesis and structural characterization of the tris(catecholate) Si(IV) -enterobactin complex and its Ge(IV) and Ti(IV) analogues. Comparative structural analysis, supported by quantum-chemical calculations, reveals the correlation between the ionic radius and the structural changes in enterobactin upon complexation.

Lantibiotics are an important class of ribosomally synthesised peptide antibiotics with a remarkable pharmacological potential. Structural variants of lantibiotics generated by peptide engineering in vivo are an important aspect for improving the peptide's efficacy, stability and bioavailability as well as production titre, which severely impacts the potential exploitation in pharmaceutical applications. Therefore, expression systems are needed which allow for a robust genetic access for ample mutagenesis experiments. Based on previous heterologous expression of the two-component lanthipeptide lichenicidin (Bliα and Bliβ) in Escherichia coli BLic5, we now employ a multigene assembly strategy for recombinant lantibiotic peptide production in the Gram-negative host. Two E. coli high copy plasmids for separate and increased expression of a two-component lantibiotic were cloned and tested for expression. From these E. coli HP expression strains, an up to 100 times increased expression was found compared with Bacillus licheniformis I89 and E. coli BLic5. Total expression yields reach 4 mg L(-1) for Bliα and 6 mg L(-1) for Bliβ. The expression system developed in this study constitutes an important cornerstone for future in vivo peptide engineering studies and is of significance for potential applications aiming at higher production titres of ribosomally synthesised, post translationally modified peptides.