POTENTIAL OF SMALL RIBOSOMALLY SYNTHESIZED BACTERIOCINS IN DESIGN OF NEW FOOD PRESERVATIVES

Abstract

ABSTRACT Nisin and subtilin are bacteriocins that are produced by Streptococcus lactis and Bacillus subtilis ATCC 6633, respectively. Nisin is important as a safe and effective food preservative. Both nisin and subtilin are ribosomally‐synthesized peptides with broad spectrum activity against gram‐positive bacteria. including many pathogenic food spoilage organisms. Since the structures of these antimicrobial bacteriocins are gene‐encoded, they provide an attractive model system for developing ways to use genetic engineering for the design and synthesis of improved and novel food preservatives, and to examine the mechanism of antibacterial action by studying the relationships between structure and function. In order to exploit these possibilities, we have cloned and characterized the genes which encode the peptide precursors of nisin and subtilin. The nisin precursor is 57 amino acids long. with a 23‐residue leader region and a 34‐residue structural region. The subtilin precursor is 56 amino acids long, with a 24‐residue leader and a 32‐residue structural region. Both precursors contain serines, threonines, and cysteines at locations that are appropriate for their involvement in the post‐translational processing events that form the unusual amino acids found in these bacteriocins. The organization of the nisin and subtilin genes was explored by SI‐mapping of the transcripts. Evolutionary relationships were observed by comparing nucleic acid sequences, amino acid sequences, and hydropathic homologies. Nisin and subtilin appear to have a common ancestry, but have been evolving separately for a long time. The striking homology in the hydropathic profiles of the leader regions of the nisin and subtilin peptide precursors indicates that hydropathicity underlies the function of the leader region. which may include participation in post‐translational processing. The similarities and differences between the structures of nisin and subtilin precursors and their respective genes provide insight about ways that their structures could be mutated without destroying processing signals in the precursor peptides. We accordingly conclude that this system will useful in the exploration of ways to use genetic engineering in the design and construction of new and improved food preservatives.