A collection of propionibacteria was screened for bacteriocin production. A new bacteriocin named propionicin T1 was isolated from two strains of Propionibacterium thoenii. This bacteriocin shows no sequence similarity to other bacteriocins. Propionicin T1 was active against all strains of Propionibacterium acidipropionici, Propionibacterium thoenii, and Propionibacterium jensenii tested and also against Lactobacillus sake NCDO 2714 but showed no activity against Propionibacterium freudenreichii. The bacteriocin was purified, and the N-terminal part of the peptide was determined with amino acid sequencing. The corresponding gene pctA was sequenced, and this revealed that propionicin T1 is produced as a prebacteriocin of 96 amino acids with a typical sec leader, which is processed to give a mature bacteriocin of 65 amino acids. An open reading frame encoding a protein of 424 amino acids was found 68 nucleotides downstream the stop codon of pctA. The N-terminal part of this putative protein shows strong similarity with the ATP-binding cassette of prokaryotic and eukaryotic ABC transporters, and this protein may be involved in self-protection against propionicin T1. Propionicin T1 is the first bacteriocin from propionibacteria that has been isolated and further characterized at the molecular level.

-Dairy propionibacteria produce a number of inhibitory compounds like propionate, acetate and diacetyl. In addition, a number of strains produce bacteriocins. Unlike lactic acid bacteria, they often produce compounds that inhibit Gram (-) bacteria as well as yeasts and molds. These dairy propionibacteria are food-grade organisms and their bacteriocins may be of interest as food preservatives. Some of their bacteriocins have been characterized. Most are heat-stable peptides containing less than 100 amino acid residues. They are insensitive to large variations in pH, and lactic acid bacteria are often more sensitive to the bacteriocins than propionibacteria. However, at present only bacteriocins with inhibitory spectra restricted to propionibacteria have been fully sequenced. Most of the bacteriocins are produced in very low amounts when the cells are grown in liquid culture, which limits their usefulness in practical applications.

No abstract

A protease-activated antimicrobial peptide (PAMP) and its inactive precursor were purified from the culture supernatant of Propionibacterium jensenii LMG 3032 and characterized at the molecular level. PAMP is a 64-amino-acid cationic peptide of 6,383 Da with physicochemical features similar to those of bacteriocins from gram-positive bacteria. This peptide displayed bactericidal activity against several propionibacteria and lactobacilli. DNA sequencing indicated that the PAMP-encoding gene (pamA) is translated as a proprotein of 198 amino acids with an N-terminal signal peptide of 27 amino acids and that PAMP constitutes the C-terminal part of this precursor. The amino acid sequence of pro-PAMP showed no similarity to those of other known proteins. By using activity tests and mass spectrometry, we showed that PAMP was formed upon protease treatment of the precursor protein. The propionibacteria produced the PAMP precursor constitutively during growth up to a level of ϳ4 mg/liter, but the producing bacteria were unable to activate the precursor. The requirement for an external protease represents a novel strategy for generating antimicrobial peptides.Antimicrobial peptides are produced by all kinds of organisms, from bacteria to mammals. In higher organisms these compounds are produced as an innate host defense mechanism to protect against pathogenic attack, whereas microorganisms presumably use these compounds as weapons in the competition for limited resources. A large number of antimicrobial peptides have been isolated from amphibians (35), fish (2, 22), insects (32), mammals (13), plants (1), and different microorganisms (12). Antimicrobial proteins and peptides from bacteria include toxins like diphtheria and cholera toxins (24, 25), bacteriolytic enzymes like lysostaphin (30) and hemolysins (8), and bacteriocins and bacteriocin-like peptides (10, 12). Numerous bacteriocins have been characterized from grampositive bacteria, and some of them show a relatively broad spectrum of inhibition. Antimicrobial peptides produced by food-grade organisms such as lactic acid bacteria and propionibacteria have received special interest due to their potential applications in food preservation (33).The classical propionibacteria have a long history of use in dairy fermentations, in particular the production of Swiss-type cheeses. A few antimicrobial peptides from these bacteria have been described so far (7,9,14,15,17,21,29), and only two bacteriocins have been characterized at the molecular level (7,17).Bacteria use a number of different mechanisms to regulate and produce active peptides and proteins. Most conventional bacteriocins are produced as precursor peptides, which are modified posttranslationally inside the cell or at the cell exterior during export to generate their biologically active forms (12). However, it has been shown that antimicrobial peptides from both bacteria (27, 28) and higher organisms (23, 31) can be produced from the degradation of larger proteins.In this work we describe a novel antimicrobial pe...

This work describes the purification and characterization of propionicin F, the first bacteriocin isolated from Propionibacterium freudenreichii. The bacteriocin has a bactericidal activity and is only active against strains of P. freudenreichii. Propionicin F appears to be formed through a processing pathway new to bacteriocins. The mass of the purified bacteriocin was determined by mass spectrometry, and the N-terminal amino acid sequence was determined by Edman degradation. Sequencing of pcfA, the bacteriocin structural gene, revealed that propionicin F corresponds to a 43-amino-acid peptide in the central part of a 255-amino-acid open reading frame, suggesting that mature propionicin F is excised from the probacteriocin by N-and C-terminal proteolytic modifications. DNA sequencing and Northern blot hybridizations revealed that pcfA is cotranscribed with genes encoding a putative proline peptidase and a protein from the radical S-adenosylmethionine family. A gene encoding an ABC transporter was also identified in close proximity to the bacteriocin structural gene. The potential role of these genes in propionicin F maturation and secretion is discussed.Propionic acid bacteria (PAB) and lactic acid bacteria (LAB) have been utilized for flavor development and preservation of food products for centuries. The preservative capacity of PAB and LAB has previously been attributed to the lowering of pH by production of propionic acid, acetic acid, and lactic acid, which are the main fermentative end products produced by these organisms. However, it has become evident that PAB and LAB also produce antimicrobial substances in addition to organic acids (25). Among these are the bacteriocins, which are gene-encoded, ribosomally synthesized peptides that usually display antimicrobial activity against species closely related to the producer organism (43).A vast number of LAB bacteriocins have been purified; some of these, including nisin, pediocin PA-1, and sakacin P, have been thoroughly characterized at the genetic and biochemical level (5,6,16,21,24,26,27,29,33,40,44,45). In general, LAB bacteriocins are small, cationic peptides, with a propensity to adopt amphiphilic helical structures (36). There are, however, exceptions from this rule, including helveticin J and enterolysin A, which both are large proteins with antimicrobial activity (23, 37). The LAB bacteriocins are usually synthesized as prepeptides, containing an N-terminal secretion signal peptide of the sec or the double-glycine type. The leader sequence is cleaved off concomitant with secretion either by the general secretory machinery or, in the case of doubleglycine leaders, by dedicated ABC transporters (15,47).In contrast to the numerous bacteriocins characterized from LAB, only three PAB bacteriocins have been identified and characterized at the amino acid and genetic level. Propionicin T1 isolated from Propionibacterium thoenii is a 65-amino-acid bacteriocin, synthesized with a 31-residue signal peptide (13). The 204-amino-acid bacteriocin SM1 from Propion...

Heterologous bacteriocin production in Propionibacterium freudenreichii is described. We developed an efficient system for DNA shuttling between Escherichia coli and P. freudenreichii using vector pAMT1. It is based on the P. freudenreichii rolling-circle replicating plasmid pLME108 and carries the cml(A)/cmx(A) chloramphenicol resistance marker. Introduction of the propionicin T1 structural gene (pctA) into pAMT1 under the control of the constitutive promoter (P 4 ) yielded bacteriocin in amounts equal to those of the wild-type producer Propionibacterium thoenii 419. The P. freudenreichii clone showed propionicin T1 activity in coculture, killing 90% of sensitive bacteria within 48 h. The pamA gene from P. thoenii 419 encoding the protease-activated antimicrobial peptide (PAMP) was cloned and expressed in P. freudenreichii, resulting in secretion of the pro-PAMP protein. Like in the wild type, PAMP activation was dependent on externally added protease. Secretion of the antimicrobial peptide was obtained from a clone in which the pamA signal peptide and PAMP were fused in frame. The promoter region of pamA was identified by fusion of putative promoter fragments to the coding sequence of the pctA gene. The P 4 and P pamp promoters directed constitutive gene expression, and activity of both promoters was enhanced by elements upstream of the promoter core region.

No abstract

The purpose of this study was to investigate the frequency of production of the bacteriocin propionicin T1 and the protease-activated antimicrobial peptide (PAMP) and their corresponding genes in 64 isolates of classical propionibacteria. This study revealed that these genes are widespread in Propionibacterium jensenii and Propionibacterium thoenii but absent from the remaining species of classical propionibacteria that were studied. The pro-PAMP-encoding gene (pamA) was found in 63% of the P. jensenii strains and 61% of the P. thoenii strains, and all of these strains displayed PAMP activity. The propionicin T1-encoding gene (pctA) was present in 89% of the P. thoenii strains and 54% of the P. jensenii strains. All P. thoenii strains containing the pctA gene exhibited antimicrobial activity corresponding to propionicin T1 activity, whereas only 38% of the pctA-containing P. jensenii strains displayed this activity. Sequencing of the pctA genes revealed the existence of two allelic variants that differed in a single nucleotide in six strains of P. jensenii; in these strains the glycine at position 55 of propionicin T1 was replaced by an aspartate residue (A variant). No strains harboring the A variant showed any antimicrobial activity against propionicin T1-sensitive bacteria. An open reading frame (orf2) located immediately downstream from the pctA gene was absent in three strains containing the G variant of propionicin T1. Two of these strains showed low antimicrobial activity, while the third strain showed no antimicrobial activity at all. The protein encoded by orf2 showed strong homology to ABC transporters, and it has been proposed previously that this protein is involved in the producer immunity against propionicin T1. The limited antimicrobial activity exhibited by the strains lacking orf2 further suggests that this putative ABC transporter plays an important role in propionicin T1 activity.Antimicrobial peptides are important components of the innate defenses in all species of organisms (8, 21). Antimicrobial peptides produced by bacteria are generally referred to as bacteriocins, which include the posttranslationally modified lantibiotics. Bacteriocins and bacteriocin-like peptides are usually ribosomally synthesized, even though it has been shown that some antimicrobial peptides from bacteria are formed by degradation of larger proteins (5,24,25).The classical propionibacteria are gram-positive bacteria with a long history of safe use in dairy fermentations, especially in the production of Swiss-type cheeses, where they are responsible for the formation of flavor and the characteristic eyes. It has also been proposed that propionibacteria may function as probiotic organisms for humans and animals (2, 17).A variety of antimicrobial compounds are produced by propionibacteria; these compounds include propionic acid, acetic acid, and diacetyl in addition to the antimicrobial peptides (9). Although a number of antimicrobial activities of propionibacteria have been reported, only three antimicrobial peptide...