Novel lantibiotics from microbial genomes

Abstract

The discovery of antibiotics was one of the most important milestones in medicine and in the fight against infectious disease. Today, more than 80% of anti-infective drugs are natural or semi-synthetic compounds. Rapidly developing superbugs, i.e. pathogens that are resistant to almost all commonly used antibiotics, have become an enormous problem. This necessitates a further search for new antibiotic substances and sources. To this end, bacteria and their huge potential to produce antimicrobials represent an inexhaustible resource. Lantibiotics (lanthionine containing antibiotics) are ribosomally produced bacterial peptide antibiotics that show interesting activities even in the nanomolar range against (multiresistant) human pathogens. The characteristic thioether aa (methyl-)lanthionine is introduced by extensive enzyme-mediated posttranslational modifications. These rare aa form intramolecular rings that are essential for the three-dimensional structure of lantibiotics, their enhanced stability against proteases and oxidation, as well as antimicrobial activity. These features make lantibiotics interesting candidates or lead structures for novel antimicrobial applications in medical and food industry. <br /> Blast searches employing a characteristic lantibiotic biosynthesis enzyme (MrsM) in the NCBI database showed that ORFs coding for proteins involved in lantibiotic production are widespread in bacteria of different phyla. Based on this genomic data mining strategy, putative lantibiotic-like gene clusters were identified in Bacillus licheniformis, Nostoc punctiforme and Caldicellulosiruptor bescii strains. The focus of this thesis was the homologous and/or heterologous expression as well as the characterization of those, so far uncharacterized, lantibiotics. In this context, the novel two-peptide lantibiotic lichenicidin that is produced by B. licheniformis DSM 13 was identified. Additionally, a partial lantibiotic gene cluster coding for proteins involved in producer self-protection against the well-known lantibiotic mersacidin is present in Bacillus amyloliquefaciens FZB42. Transfer of the biosynthetic part of the mersacidin gene cluster to B. amyloliquefaciens FZB42 resulted in successful expression of fully modified and active mersacidin in this strain.