Nisin A is a potent antimicrobial with potential as an alternative to traditional antibiotics, and a number of genetically modified variants have been created that target clinically relevant pathogens. In addition to antimicrobial activity, nisin autoregulates its own production via a signal transduction pathway, a property that has been exploited in a protein expression system termed the nisin-controlled gene expression (NICE) system. Although NICE has become one of the most popular protein expression systems, one drawback is that the inducer peptide, nisin A, also has inhibitory activity. It has already been demonstrated that the N-terminal region of nisin A contributes to antimicrobial activity and signal transduction properties; therefore, we conducted bioengineering of nisin at positions Pro9 and Gly10 within ring B to produce a bank of variants that could potentially be used as alternative induction peptides. One variant, designated nisin M, has threonines at positions 9 and 10 and retains induction capacity comparable to that of wild-type nisin A, while most of the antimicrobial activity is abolished. Further analysis confirmed that nisin M produces a mix of peptides as a result of different degrees of dehydration of the two threonines. We show that nisin M exhibits potential as a more suitable alternative to nisin A for the expression of proteins that may be difficult to express or for production of proteins in strains that are sensitive to wild-type nisin. Moreover, it may address the increasing demand by industry for optimization of peptide fermentations to increase yields or production rates. IMPORTANCE This study describes the generation of a nisin variant with superior characteristics for use in the NICE protein expression system. The variant, termed nisin M, retains an induction capacity comparable to that of wild-type nisin A but exhibits significantly reduced antimicrobial activity and can therefore be used at concentrations that are normally toxic to the expression host.

While nisin (lantibiotic), lacticin 3147 (lantibiotic) and vancomycin (glycopeptides) are among the best studied lipid II-binding antimicrobials, their relative activities have never been compared. Nisin and lacticin 3147 have been employed/investigated primarily as food preservatives, although they do have potential in terms of veterinary and clinical applications. Vancomycin is used exclusively in clinical therapy. We reveal a higher potency for lacticin 3147 (MIC 0.95-3.8 μg/ml) and vancomycin (MIC 0.78-1.56 μg/ml) relative to that of nisin (MIC 6.28-25.14 μg/ml) against the food-borne pathogen Listeria monocytogenes. A comparison of the activity of the three antimicrobials against nisin resistance mutants of L. monocytogenes also reveals that their susceptibility to vancomycin and lacticin 3147 changed only slightly or not at all. A further assessment of relative activity against a selection of Bacillus cereus, Enterococcus and Staphylococcus aureus targets revealed that vancomycin MICs consistently ranged between 0.78 and 1.56 μg/ml against all but one strain. Lacticin 3147 was found to be more effective than nisin against B. cereus (lacticin 3147 MIC 1.9-3.8 μg/ml; nisin MIC 4.1-16.7 μg/ml) and E. faecium and E. faecalis targets (lacticin 3147 MIC from 1.9 to 3.8 μg/ml; nisin MIC ≥8.3 μg/ml). The greater effectiveness of lacticin 3147 is even more impressive when expressed as molar values. However, in agreement with the previous reports, nisin was the more effective of the two lantibiotics against S. aureus strains. This study highlights that in many instances the antimicrobial activity of these leading lantibiotics are comparable with that of vancomycin and emphasizes their particular value with respect to use in situations including foods and veterinary medicine, where the use of vancomycin is not permitted.

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