Nisin E, a New Nisin Variant Produced by Streptococcus equinus MDC1

Abstract

Members of the genus Streptococcus inhabit a variety of sites in humans and other animals and some species are prolific producers of proteinaceous antibiotics (bacteriocins). As little is known about (i) streptococci inhabiting domestic pets, and (ii) whether novel bacteriocin-producing streptococci can be isolated from domestic pets, the aim of this study is to address these gaps in the research literature. In this study, Streptococcus equinus MDC1, isolated from a healthy dog, was found to exhibit potent antibacterial activity against Micrococcus luteus in a simultaneous antagonism assay, suggesting that strain MDC1 produces a lantibiotic bacteriocin. The inhibitory activity spectrum of S. equinus MDC1, determined using agar-based deferred antagonism assays against >70 indicator strains, was found to be similar to that of nisin U (a lantibiotic produced by Streptococcus uberis). However, the spectra of the two bacteriocins differed by 23 strains, mainly with the MDC1 bacteriocin having no inhibitory activity towards certain streptococci of human origin (e.g., Streptococcus gordonii, Streptococcus anginosus, Streptococcus salivarius). The genome of S. equinus MDC1, which was sequenced completely using single-molecule real-time (SMRT) next-generation DNA sequencing technology, comprises a single 1,936,555-basepair chromosome containing seven copies of the ribosomal RNA operon, 69 tRNA genes and nearly 1900 putative coding sequences. Analysis of the MDC1 genome sequence using the bacteriocin detection algorithms BAGEL4 and antiSMASH revealed the location of a 13,164-basepair 11-gene locus, designated nmd, which encoded a mature nisin E peptide that differed from nisin U by only two amino acids (Ile15→Ala and Leu21→Ile) and an extra C-terminal asparagine residue, and the proteins required for post-translational modification of the bacteriocin, processing, export, and producer immunity. Despite the high homology (90.6% identity, 93.8% similarity) between nisin E and nisin U, there was considerably less homology (47.4–76.3% identity, 68.4–88.8% similarity) between the other proteins encoded by their respective biosynthetic loci. This new natural variant of nisin, called nisin E, represents the first nisin variant to be reported for S. equinus; additionally, its differences with nisin U may provide some insight into the amino acids that influence bacteriocin potency and killing spectrum.

Activity of Gut-Derived Nisin-like Lantibiotics against Human Gut Pathogens and Commensals

“…However, how nisin and nisin-like lantibiotics might impact the human gut microbiome has not been elucidated, nor has the presence of nisin-like compounds in the human gut microbiome been investigated in detail. The recent discovery of blauticin and nisin analogs clearly indicates that nisin-like molecules are encoded in the human microbiome, ,,, with other analogs detected in the microbiome of other mammals. , To first explore the biosynthetic potential of the gut microbiome for lantibiotic production, we systematically performed bioinformatic mining with RODEO for nisin-like lantibiotics derived from gut bacterial genomes. Subsequent filtering, multiple sequence alignment, and manual curation discovered six gut-derived nisin-like lantibiotics, four of which were not reported previously.…”

Nisin S, a Novel Nisin Variant Produced by Ligilactobacillus salivarius P1CEA3

“…One of the clusters encodes salivaricin B (presalivaricin B from L. salivarius M6) and the bacteriocin Abp118 (Abp118α + Abp118β). The SalB encoded by L. salivarius P1ACE3 ( Figure 1 b) differs in one amino acid (V6I) with the presalivaricin B of L. salivarius M7 [ 23 ] and in two amino acids (V6I and K43I) with the presalivaricin B encoded by L. salivarius UCC118 [ 22 ]. However, peptides identical to SalB in L. salivarius P1ACE3 have been encoded by other L. salivarius strains [ 39 ], with no additional data for its expression, processing, and/or secretion.…”

“…The amino acid substitution T25S in nisin S involves the formation of a lanthionine bridge that stabilizes the E ring, instead of a 3-methyllanthionine bridge stabilizing the E ring in nisin A ( Figure 6 ). At position 27 and within the E ring, nisin S (H27G) shows a hydrophobic residue (G) while nisin A has a polar amino acid (H), a substitution also observed in nisin P, nisin O, nisin U, nisin U2, and nisin E [ 18 , 20 , 21 , 23 , 56 ]. This substitution could confer nisin S has a stronger ability to permeate membranes and support, in part, its antimicrobial activity against Gram-negative bacteria such as E. coli , something documented for nisin J which has a hydrophobic residue at position 20 of its molecule [ 8 ].…”

“…For alignment and phylogeny reconstruction of the nisin variants, the MEGA11 software was used [ 35 ]. a Molecular weight (MW) of nisin variants in daltons, and b reference is given when the accession number is not available [ 20 , 21 , 22 , 23 ].…”

“…Since its discovery, twelve natural variants of nisin (nisin A, Z, Q, U, U2, F, H, O, J, P, G, and E) [ 8 , 12 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 ] and two nisin-like bacteriocins (salivaricin D and kunkecin A) [ 24 , 25 ] have been characterized. Natural nisin variants are between 31 and 35 amino acid long and have been identified as produced by the bacterial species Lactococcus lactis (nisin A, Z, F, and Q), Streptococcus sp.…”