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.