Nisin E Is a Novel Nisin Variant Produced by Multiple Streptococcus equinus Strains

Area of Science:

• Microbiology and Molecular Biology
• Antimicrobial Peptides
• Food Science and Technology

Background:

• Nisin A is a well-established lantibiotic used as a food preservative with therapeutic potential.
• Lantibiotics are ribosomally synthesized and post-translationally modified peptides with antimicrobial activity.
• The discovery of novel lantibiotic variants can expand their applications and understanding of microbial defense mechanisms.

Purpose of the Study:

• To characterize a novel nisin variant, termed nisin E, produced by *Streptococcus equinus*.
• To investigate the genetic basis and antimicrobial spectrum of nisin E.
• To explore the prevalence and regulatory role of nisin E in *Streptococcus equinus*.

Main Methods:

• Isolation and identification of *Streptococcus equinus* strains from sheep milk.
• Shotgun whole genome sequencing and bioinformatic analysis of biosynthetic gene clusters.
• MALDI-TOF mass spectrometry for peptide characterization.
• Antimicrobial activity assays against various bacterial species.
• Sequence alignment and pangenome analysis to identify nisin E operons and associated genes.

Main Results:

• Nisin E, a 3100.8 Da peptide, was identified with 75% identity to nisin A, featuring unique sequence variations.
• Nisin E-producing strains demonstrated inhibitory activity against *Lactobacillus*, *Bacillus*, and *Clostridiodes* species.
• Six nisin E operons were detected in *S. equinus* genomes, with widespread distribution of nisin E transport/immunity genes.

Conclusions:

• Nisin E represents a novel lantibiotic with distinct antimicrobial properties and genetic organization.
• The widespread presence of nisin E genes suggests a significant role in the competitive interactions of *S. equinus*.
• This discovery expands the known diversity of nisin variants and their ecological significance.