Lantibiotic paenibacillin

N-terminal acetylation was uncovered in paenibacillin, a novel lantibiotic recently reported as a product of Paenibacillus polymyxa OSY-DF. This N-terminal modification is unprecedented among bacteria-derived antimicrobial peptides and further illustrates the broad range of modifications that can occur in lantibiotics. Additionally, the primary structure of paenibacillin has been finally determined unequivocally by the extensive NMR analysis taken together with previous MS/MS results. These analyses revealed the structure of paenibacillin as one of the most post-translationally modified lantibiotics.

Industrial production of paenibacillin, and similar rare antimicrobial peptides, is hampered by low productivity of the producing microorganisms and lack of efficient methods to recover these peptides from fermentor or bioreactor end products. Preliminary data showed that paenibacillin was preferentially partitioned in foam accumulated during growth of the producer, Paenibacillus polymyxa, in aerated liquid media. This research was initiated to improve the production and recovery of paenibacillin in bioreactors by maximizing partitioning of this antimicrobial agent in the collected foam. This was completed through harvesting foam continuously during paenibacillin production, using modified bioreactor, and optimizing bioreaction conditions through response surface methodology (RSM). During initial screening, the following factors were tested using 400 mL inoculated media in 2 L bioreactors: medium (tryptic soy broth, TSB, with or without added yeast extract), airflow (0 or 0.8 L/min; LPM), stir speed (300 or 500 revolution/min; RPM), incubation temperature (30 or 36 °C), and incubation time (16 or 24 h). Results showed that airflow, time, and stir speed had significant effects (p < 0.05) on paenibacillin recovery in the collected collapsed foam (foamate). These factors were varied together to follow the path of steepest assent to maximize paenibacillin concentration. Once the local maximum was found, RSM was completed with a central composite design to fine-tune the bioreaction parameters. The optimization experiments proved that the significant parameters and their optimal conditions for paenibacillin concentration in the foam were: incubation at 30 °C for 23 h with airflow of 0.95 LPM, and agitation speed of 450 RPM. These conditions increased paenibacillin concentration, predicted by RSM, from 16 µg/mL in bioreaction without foam collection to 743 µg/mL collected in foamate. The optimized conditions also almost doubled the yield of paenibacillin measured in the foam collected from a bioreaction run (12,674 µg/400 mL bioreaction) when compared to that obtained from a run without foam collection (6400 µg/400 mL bioreaction). Results of this study could improve the feasibility of commercial production and downstream processing of paenibacillin and similar novel antimicrobial peptides. Availability of such peptides will eventually help in protecting perishable products against pathogenic and spoilage bacteria.

Paenibacillin, a recently-discovered lantibiotic from Paenibacillus polymyxa OSY-DF, showed potency against Listeria monocytogenes, methicillin-resistant Staphylococcus aureus and other Gram-positive bacteria. The chemical structure of paenibacillin has been determined previously. This study was initiated to investigate the biosynthesis of paenibacillin, and to reveal unique features in its biosynthetic pathway. Paenibacillin structural gene (paeA) was identified by polymerase chain reaction (PCR) analysis. The complete biosynthetic gene cluster was revealed by whole genome sequencing of the producer strain. The paenibacillin gene cluster (11.7 kb) comprises 11 open reading frames (ORFs) encoding proteins for production, modification, regulation, immunity and transportation of the lantibiotic. Disruption of the gene encoding lantibiotic dehydratase (PaeB) completely eliminated the production of paenibacillin. The cluster includes a gene encoding a putative acetylase (PaeN), which may catalyze the N-terminal acetylation of paenibacillin during its biosynthesis. This finding supports the results of a previous chemical analysis, reporting an acetyl moiety uniquely located at paenibacillin N-terminus. Results of this study may expedite efforts to design effective lantibiotic drugs and facilitate attempts to increase the productivity of the lantibiotic-producing strain.