Bacteriocins of gram-positive bacteria

Cloning and genetic organization of the bacteriocin 31 determinant encoded on the Enterococcus faecalis pheromone-responsive conjugative plasmid pYI17

The conjugative plasmid pYI17 (57.5 kb) isolated from Enterococcus faecalis YI717 confers a pheromone response on the host and encodes the bacteriocin 31 gene. Bacteriocin 31 is active against E. hirae 9790, E. faecium, and Listeria monocytogenes. pYI17 was mapped physically by restriction enzyme analysis and the relational clone method. Deletion mutant and sequence analyses of the EcoRI fragment B cloned from pYl17 revealed that a 1.0-kb fragment contained the bacteriocin gene (bacA) and an immunity gene (bacB). This fragment induced bacteriocin activity in E. faecalis OG1X and E. hirae 9790. The bacA gene is located on the pYI17 physical map between 3.37 and 3.57 kb, and bacB is located between 3.59 kb and 3.87 kb, bacA encodes 67 amino acids, and bacB encodes 94 amino acids. The deduced amino acid sequence of the bacA protein contained a series of hydrophobic residues typical of a signal sequence at its amino terminus. The predicted mature bacA protein (43 amino acids) showed sequence homology with the membrane-active class II bacteriocins of lactic acid bacteria. Analysis of Tn5 insertion mutants and the resulting transcripts indicated that these genes are transcribed as an operon composed of bacA, bacB, and an open reading frame located downstream of bacB designated ORF3.

Variacin, a new lanthionine-containing bacteriocin produced by Micrococcus varians: comparison to lacticin 481 of Lactococcus lactis

A new lanthionine-containing bacteriocin, variacin, displaying a broad host range of inhibition against gram-positive food spoilage bacteria, has been identified from two strains of Micrococcus varians isolated from meat fermentations. The new bacteriocin was purified, and its amino-terminal end and total amino acid composition were determined. The structural gene was isolated and analyzed. Variacin is resistant to heat and pH conditions from 2 to 10. Its primary sequence shows significant homology to lacticin 481 to Lactococcus lactis, which is more pronounced for the probacteriocin than for the leader sequence. Variacin, like lacticin 481, contains lanthionine and beta-methyllanthionine residues, but its leader sequence clearly resembles nonlantibiotic leader sequences. In particular, the prepeptide contains glycine residues at positions -1 and -2 of the processing site.

Antagonistic effect of oral bacteria towards Treponema denticola

This study was designed to isolate oral bacteria exhibiting antagonism towards Treponema denticola and to characterize the inhibitory activity. Eleven bacterial isolates obtained from subgingival sites and identified as either Staphylococcus aureus or Streptococcus mutans were found to inhibit the growth of T. denticola. When the activity spectra of these isolates were analyzed, two additional periodontopathogens (Porphyromonas gingivalis and Prevotella intermedia) were found to be affected, whereas most gram-positive bacteria were not. Strains of S. aureus produce a bacteriocin-like inhibitory substance (heat stable and protease sensitive), whereas the inhibitory effect of S. mutans appears to be related to the production of lactic acid. The negative interactions reported in this paper may govern population shifts observed in subgingival sites.

Induction of bacteriocin production in Lactobacillus sake by a secreted peptide

Lactobacillus sake LTH673 is known to produce a bacteriocin called sakacin P. Production of and immunity to sakacin P were found to depend on the presence of a protease-sensitive component that is produced by L. sake LTH673 itself. This component (called inducing factor [IF]) was purified from culture supernatants and shown to be a basic, nonbacteriocin peptide consisting of 19 amino acids, which in principle is capable of forming a highly amphiphilic helical structure. Circular dichroism studies showed that IF indeed could adopt a helical structure, but only in membrane-mimicking environments. Both purified IF and chemically synthesized IF induced expression of the structural gene for sakacin P and concomitant secretion of the gene product. In addition, IF induced its own production and immunity to sakacin P and related bacteriocins. These results indicate that bacteriocin production by L. sake LTH673 is controlled by an autoinduction pathway in which IF may function as a cell density signal.

Nucleotide sequence and taxonomical distribution of the bacteriocin gene lin cloned from Brevibacterium linens M18

Linocin M18 is an antilisterial bacteriocin produced by the red smear cheese bacterium Brevibacterium linens M18. Oligonucleotide probes based on the N-terminal amino acid sequence were used to locate its single copy gene, lin, on the chromosomal DNA. The amino acid composition, N-terminal sequence, and molecular mass derived from the nucleotide sequence of an open reading frame of 798 nucleotides coding for 266 amino acids found on a 3-kb BamHI restriction fragment correspond closely to those obtained from the purified protein (N. Valdés-Stauber and S. Scherer, Appl. Environ. Microbiol. 60:3809-3814, 1994). No sequence homology to any protein or nucleotide sequences deposited in databases was found. Comparison of the nucleotide sequence and the N-terminal amino acid sequence derived from the protein suggests that B. linens M18 produces an N-formyl-methionyl-CAC tRNA. A wide taxonomical distribution of the gene within coryneform bacteria has been demonstrated by PCR amplification. The structural gene from linocin M18 is present at least in three Brevibacterium species, five Arthrobacter species, and five Corynebacterium species.

Comparison of lantibiotic gene clusters and encoded proteins

Lantibiotics form a group of modified peptides with unique structures, containing post-translationally modified amino acids such as dehydrated and lanthionine residues. In the gram-positive bacteria that secrete these lantibiotics, the gene clusters flanking the structural genes for various linear (type A) lantibiotics have recently been characterized. The best studied representatives are those of nisin (nis), subtilin (spa), epidermin (epi), Pep5 (pep), cytolysin (cyl), lactocin S (las) and lacticin 481 (lct). Comparison of the lantibiotic gene clusters shows that they contain conserved genes that probably encode similar functions. The nis, spa, epi and pep clusters contain lanB and lanC genes that are presumed to code for two types of enzymes that have been implicated in the modification reactions characteristic of all lantibiotics, i.e. dehydration and thio-ether ring formation. The cyl, las and lct gene clusters have no homologue of the lanB gene, but they do contain a much larger lanM gene that is the lanC gene homologue. Most lantibiotic gene clusters contain a lanP gene encoding a serine protease that is presumably involved in the proteolytic processing of the prelantibiotics. All clusters contain a lanT gene encoding an ABC transporter likely to be involved in the export of (precursors of) the lantibiotics. The lanE, lanF and lanG genes in the nis, spa and epi clusters encode another transport system that is possibly involved in self-protection. In the nisin and subtilin gene clusters two tandem genes, lanR and lanK, have been located that code for a two-component regulatory system. Finally, non-homologous genes are found in some lantibiotic gene clusters. The nisI and spaI genes encode lipoproteins that are involved in immunity, the pepI gene encodes a membrane-located immunity protein, and epiD encodes an enzyme involved in a post-translational modification found only in the C-terminus of epidermin. Several genes of unknown function are also found in the las gene cluster. A database has been assembled for all putative gene products of type A lantibiotic gene clusters. Database searches, multiple sequence alignment and secondary structure prediction have been used to identify conserved sequence segments in the LanB, LanC, LanE, LanF, LanG, LanK, LanM, LanP, LanR and LanT gene products that may be essential for structure and function. This database allows for a rapid screening of newly determined sequences in lantibiotic gene clusters.

An application in cheddar cheese manufacture for a strain of Lactococcus lactis producing a novel broad-spectrum bacteriocin, lacticin 3147

Lactococcus lactis DPC3147, a strain isolated from an Irish kefir grain, produces a bacteriocin with a broad spectrum of inhibition. The bacteriocin produced is heat stable, particularly at a low pH, and inhibits nisin-producing (Nip+) lactococci. On the basis of the observation that the nisin structural gene (nisA) does not hybridize to DPC3147 genomic DNA, the bacteriocin produced was considered novel and designated lacticin 3147. The genetic determinants which encode lacticin 3147 are contained on a 63-kb plasmid, which was conjugally mobilized to a commercial cheese starter, L. lactis subsp. cremoris DPC4268. The resultant transconjugant, DPC4275, both produces and is immune to lacticin 3147. The ability of lacticin 3147-producing lactococci to perform as cheddar cheese starters was subsequently investigated in cheesemaking trials. Bacteriocin-producing starters (which included the transconjugant strain DPC4275) produced acid at rates similar to those of commercial strains. The level of lacticin 3147 produced in cheese remained constant over 6 months of ripening and correlated with a significant reduction in the levels of nonstarter lactic acid bacteria. Such results suggest that these starters provide a means of controlling developing microflora in ripened fermented products.