Propionicin SM1, a bacteriocin from Propionibacterium jensenii DF1: isolation and characterization of the protein and its gene

Growth Control of Listeria monocytogenes in Raw Sausage via Bacteriocin-Producing Leuconostoc carnosum DH25

The current study addresses the critical issue of Listeria monocytogenes growth in raw sausage/meat products leading to human infections, most commonly listeriosis, which is known for its high fatality rate. This research focuses on the isolation, identification, and screening of lactic acid bacteria from various meat and fish products in Switzerland. In total, 274 lactic acid bacteria strains were isolated from 30 different products and were screened for their ability to inhibit Listeria monocytogenes growth, with 51 isolates demonstrating anti-Listeria activity at 8 °C, 15 °C, 25 °C, and 37 °C. Further experiments, using a meat model and a raw sausage challenge test, demonstrated that Leuconostoc carnosum DH25 significantly inhibited Listeria monocytogenes growth during the ripening and storage of the tested meat/sausage. This inhibitory effect was found to be attributed to the bacteriocins produced by Leuconostoc carnosum DH25 rather than factors like pH or water activity. The stability of the anti-Listeria substances was examined, revealing their resistance to temperature and pH changes, making Leuconostoc carnosum DH25 a promising protective culture for raw sausages. The genome sequencing of this strain confirms its safety, with no antibiotic resistance genes or virulence factors detected, and reveals the presence of the structural genes for the production of the bacteriocin LeucocinB-Ta11a. This study underscores the potential of LAB strains and their bacteriocins as effective tools for enhancing food safety and preventing Listeria monocytogenes growth in meat products, offering valuable insights into biocontrol strategies in the food industry.

Bifidobacterium longum subsp. infantis as widespread bacteriocin gene clusters carrier stands out among the Bifidobacterium

Bifidobacterium is the dominant genus, particularly in the intestinal tract niche of healthy breast-fed infants, and many of these strains have been proven to elicit positive effects on infant development. In addition to its effective antimicrobial activity against detrimental microorganisms, it helps to improve the intestinal microbiota balance. The isolation and identification of bacteriocins from Bifidobacterium have been limited since the mid-1980s, leading to an underestimation of its ability for bacteriocin production. Here, we employed a silicon-based search strategy to mine 354 putative bacteriocin gene clusters (BGCs), most of which have never been reported, from the genomes of 759 Bifidobacterium strains distributed across 9 species. Consistent with previous reports, most Bifidobacterium strains did not carry or carry only a single BGC; however, Bifidobacterium longum subsp. infantis, in contrast to other Bifidobacterium species, carried numerous BGCs, including lanthipeptides, lasso peptides, thiopeptides, and class IId bacteriocins. The antimicrobial activity of the crude bacteriocins and transcription analysis confirmed its potential for bacteriocin biosynthesis. Additionally, we investigated the association of bacteriocins with the phylogenetic positions of their homologs from other genera and niches. In conclusion, this study re-examines a few Bifidobacterium species traditionally regarded as a poor source of bacteriocins. These bacteriocin genes impart a competitive advantage to Bifidobacterium in colonizing the infant intestinal tract. IMPORTANCE Development of the human gut microbiota commences from birth, with bifidobacteria being among the first colonizers of the newborn intestinal tract and dominating it for a considerable period. To date, the genetic basis for the successful adaptation of bifidobacteria to this particular niche remains unclear since studies have mainly focused on glycoside hydrolase and adhesion-related genes. Bacteriocins are competitive factors that help producers maintain colonization advantages without destroying the niche balance; however, they have rarely been reported in Bifidobacterium. The advancement in sequencing methods and bacteriocin databases enables the use of a silicon-based search strategy for the comprehensive and rapid re-evaluation of the bacteriocin distribution of Bifidobacterium. Our study revealed that B. infantis carries abundant bacteriocin biosynthetic gene clusters for the first time, presenting new evidence regarding the competitive interactions of Bifidobacterium in the infant intestinal tract.

Comparative Genomic Analysis of Bifidobacterium bifidum Strains Isolated from Different Niches

The potential probiotic benefits of Bifidobacterium bifidum have received increasing attention recently. We used comparative genomic analysis to explore the differences in the genome and the physiological characteristics of B. bifidum isolated from the fecal samples of Chinese adults and infants. The relationships between genotypes and phenotypes were analyzed to assess the effects of isolation sources on the genetic variation of B. bifidum. The phylogenetic tree results indicated that the phylogeny of B. bifidum may be related to the geographical features of its isolation source. B. bifidum was found to have an open pan-genome and a conserved core genome. The genetic diversity of B. bifidum is mainly reflected in carbohydrate metabolism- and immune/competition-related factors, such as the glycoside hydrolase gene family, bacteriocin operons, antibiotic resistance genes, and clustered regularly interspaced short palindromic repeats (CRISPR)-Cas. Additionally, the type III A CRISPR-Cas system was discovered in B. bifidum for the first time. B. bifidum strains exhibited niche-specific characteristics, and the results of this study provide an improved understanding of the genetics of this species.

New Insight into Antimicrobial Compounds from Food and Marine-Sourced Carnobacterium Species through Phenotype and Genome Analyses

Carnobacteriummaltaromaticum and Carnobacteriumdivergens, isolated from food products, are lactic acid bacteria known to produce active and efficient bacteriocins. Other species, particularly those originating from marine sources, are less studied. The aim of the study is to select promising strains with antimicrobial potential by combining genomic and phenotypic approaches on large datasets comprising 12 Carnobacterium species. The biosynthetic gene cluster (BGCs) diversity of 39 publicly available Carnobacterium spp. genomes revealed 67 BGCs, distributed according to the species and ecological niches. From zero to six BGCs were predicted per strain and classified into four classes: terpene, NRPS (non-ribosomal peptide synthetase), NRPS-PKS (hybrid non-ribosomal peptide synthetase-polyketide synthase), RiPP (ribosomally synthesized and post-translationally modified peptide). In parallel, the antimicrobial activity of 260 strains from seafood products was evaluated. Among the 60% of active strains, three genomes were sequenced and submitted to a dereplication process. C. inhibens MIP2551 produced a high amountof H₂O₂, probably thanks to the presence of four oxidase-encoding genes. C. maltaromaticum EBP3019 and SF668 strains were highly efficient against Listeria monocytogenes. A new extracellular 16 kDa unmodified bacteriocin in the EBP3019 strain and five different bacteriocins in SF668 were highlighted. In this study, the overview of antimicrobial BGC and inhibitory activities of Carnobacterium spp. allowed the prediction of potential innovative natural products that could be relevant for biotechnological applications.

Red-Brown Pigmentation of Acidipropionibacterium jensenii Is Tied to Haemolytic Activity and cyl-Like Gene Cluster

The novel Acidipropionibacterium genus encompasses species of industrial importance but also those associated with food spoilage. In particular, Acidipropionibacterium acidipropionici, Acidipropionibacterium thoenii, and Acidipropionibacterium jensenii play an important role in food fermentation, as biopreservatives, or as potential probiotics. Notably, A. jensenii and A. thoenii can cause brown spot defects in Swiss-type cheeses, which have been tied to the rhamnolipid pigment granadaene. In the pathogenic bacterium Streptococcus agalactiae, production of granadaene depends on the presence of a cyl gene cluster, an important virulence factor linked with haemolytic activity. Here, we show that the production of granadaene in pigmented Acidipropionibacterium, including A. jensenii, A. thoenii, and Acidipropionibacterium virtanenii, is tied to haemolytic activity and the presence of a cyl-like gene cluster. Furthermore, we propose a PCR-based test, which allows pinpointing acidipropionibacteria with the cyl-like gene cluster. Finally, we present the first two whole genome sequence analyses of the A. jensenii strains as well as testing phenotypic characteristics important for industrial applications. In conclusion, the present study sheds light on potential risks associated with the presence of pigmented Acidipropionibacterium strains in food fermentation. In addition, the results presented here provide ground for development of a quick and simple diagnostic test instrumental in avoiding potential negative effects of Acidipropionibacterium strains with haemolytic activity on food quality.

Acidipropionibacterium virtanenii sp. nov., isolated from malted barley

A Gram-stain-positive, catalase-positive and pleomorphic rod organism was isolated from malted barley in Finland, classified initially by partial 16S rRNA gene sequencing and originally deposited in the VTT Culture Collection as a strain of Propionibacterium acidipropionici (currently Acidipropionibacterium acidipropionici). The subsequent comparison of the whole 16S rRNA gene with other representatives of the genus Acidipropionibacterium revealed that the strain belongs to a novel species, most closely related to Acidipropionibacterium microaerophilum and Acidipropionibacterium acidipropionici, with similarity values of 98.46 and 98.31 %, respectively. The whole genome sequencing using PacBio RS II platform allowed further comparison of the genome with all of the other DNA sequences available for the type strains of the Acidipropionibacterium species. Those comparisons revealed the highest similarity of strain JS278^T to A. acidipropionici, which was confirmed by the average nucleotide identity analysis. The genome of strain JS278^T is intermediate in size compared to the A. acidipropionici and Acidipropionibacterium jensenii at 3 432 872 bp, the G+C content is 68.4 mol%. The strain fermented a wide range of carbon sources, and produced propionic acid as the major fermentation product. Besides its poor ability to grow at 37 °C and positive catalase reaction, the observed phenotype was almost indistinguishable from those of A. acidipropionici and A. jensenii. Based on our findings, we conclude that the organism represents a novel member of the genus Acidipropionibacterium, for which we propose the name Acidipropionibacteriumvirtanenii sp. nov. The type strain is JS278^T (=VTT E-113202^T=DSM 106790^T).

Propionibacterium spp.-source of propionic acid, vitamin B12, and other metabolites important for the industry

Bacteria from the Propionibacterium genus consists of two principal groups: cutaneous and classical. Cutaneous Propionibacterium are considered primary pathogens to humans, whereas classical Propionibacterium are widely used in the food and pharmaceutical industries. Bacteria from the Propionibacterium genus are capable of synthesizing numerous valuable compounds with a wide industrial usage. Biomass of the bacteria from the Propionibacterium genus constitutes sources of vitamins from the B group, including B12, trehalose, and numerous bacteriocins. These bacteria are also capable of synthesizing organic acids such as propionic acid and acetic acid. Because of GRAS status and their health-promoting characteristics, bacteria from the Propionibacterium genus and their metabolites (propionic acid, vitamin B12, and trehalose) are commonly used in the cosmetic, pharmaceutical, food, and other industries. They are also used as additives in fodders for livestock. In this review, we present the major species of Propionibacterium and their properties and provide an overview of their functions and applications. This review also presents current literature concerned with the possibilities of using Propionibacterium spp. to obtain valuable metabolites. It also presents the biosynthetic pathways as well as the impact of the genetic and environmental factors on the efficiency of their production.

The commensal lifestyle of Staphylococcus aureus and its interactions with the nasal microbiota

Although human colonization by facultative bacterial pathogens, such as Staphylococcus aureus, represents a major risk factor for invasive infections, the commensal lifestyle of such pathogens has remained a neglected area of research. S. aureus colonizes the nares of approximately 30% of the human population and recent studies suggest that the composition of highly variable nasal microbiota has a major role in promoting or inhibiting S. aureus colonization. Competition for epithelial attachment sites or limited nutrients, different susceptibilities to host defence molecules and the production of antimicrobial molecules may determine whether nasal bacteria outcompete each other. In this Review, we discuss recent insights into mechanisms that are used by S. aureus to prevail in the human nose and the counter-strategies that are used by other nasal bacteria to interfere with its colonization. Understanding such mechanisms will be crucial for the development of new strategies for the eradication of endogenous facultative pathogens.

Engineering propionibacteria as versatile cell factories for the production of industrially important chemicals: advances, challenges, and prospects

Propionibacteria are actinobacteria consisting of two principal groups: cutaneous and dairy. Cutaneous propionibacteria are considered primary pathogens to humans, whereas dairy propionibacteria are widely used in the food and pharmaceutical industries. Increasing attention has been focused on improving the performance of dairy propionibacteria for the production of industrially important chemicals, and significant advances have been made through strain engineering and process optimization in the production of flavor compounds, nutraceuticals, and antimicrobial compounds. In addition, genome sequencing of several propionibacteria species has been completed, deepening understanding of the metabolic and physiological features of these organisms. However, the metabolic engineering of propionibacteria still faces several challenges owing to the lack of efficient genome manipulation tools and the existence of various types of strong restriction-modification systems. The emergence of systems and synthetic biology provides new opportunities to overcome these bottlenecks. In this review, we first introduce the major species of propionibacteria and their properties and provide an overview of their functions and applications. We then discuss advances in the genome sequencing and metabolic engineering of these bacteria. Finally, we discuss systems and synthetic biology approaches for engineering propionibacteria as efficient and robust cell factories for the production of industrially important chemicals.

Development of a Propionibacterium-Escherichia coli shuttle vector for metabolic engineering of Propionibacterium jensenii, an efficient producer of propionic acid

Propionic acid (PA) is an important chemical building block and is widely applied for organic synthesis, food, feedstuff, and pharmaceuticals. To date, the strains that can efficiently produce PA have included Propionibacterium thoenii, P. freudenreichii, and P. acidipropionici. In this report, we show that P. jensenii ATCC 4868 is also able to produce PA in much higher yields than the previously reported strains. To further improve the production capacity, a P. jensenii-Escherichia coli shuttle vector was developed for the metabolic engineering of P. jensenii. Specifically, a 6.9-kb endogenous plasmid, pZGX01, was isolated from P. acidipropionici ATCC 4875 and sequenced. Since the sequencing analysis indicated that pZGX01 could encode 11 proteins, the transcriptional levels of the corresponding genes were also investigated. Then, a P. jensenii-Escherichia coli shuttle vector was constructed using the pZGX01 plasmid, the E. coli pUC18 plasmid, and a chloramphenicol resistance gene. Interestingly, not only could the developed shuttle vector be transformed into P. jensenii ATCC 4868 and 4870, but it also could be transformed into freudenreichii ATCC 6207 subspecies of P. freudenreichii. Finally, the glycerol dehydrogenase gene (gldA) from Klebsiella pneumoniae was expressed in P. jensenii ATCC 4868 with the constructed shuttle vector. In a 3-liter batch culture, the PA production by the engineered P. jensenii ATCC 4868 strain reached 28.23 ± 1.0 g/liter, which was 26.07% higher than that produced by the wild-type strain (22.06 ± 1.2 g/liter). This result indicated that the constructed vector can be used a useful tool for metabolic engineering of P. jensenii.

The genome sequence of Propionibacterium acidipropionici provides insights into its biotechnological and industrial potential

BACKGROUND

Synthetic biology allows the development of new biochemical pathways for the production of chemicals from renewable sources. One major challenge is the identification of suitable microorganisms to hold these pathways with sufficient robustness and high yield. In this work we analyzed the genome of the propionic acid producer Actinobacteria Propionibacterium acidipropionici (ATCC 4875).

RESULTS

The assembled P. acidipropionici genome has 3,656,170 base pairs (bp) with 68.8% G + C content and a low-copy plasmid of 6,868 bp. We identified 3,336 protein coding genes, approximately 1000 more than P. freudenreichii and P. acnes, with an increase in the number of genes putatively involved in maintenance of genome integrity, as well as the presence of an invertase and genes putatively involved in carbon catabolite repression. In addition, we made an experimental confirmation of the ability of P. acidipropionici to fix CO2, but no phosphoenolpyruvate carboxylase coding gene was found in the genome. Instead, we identified the pyruvate carboxylase gene and confirmed the presence of the corresponding enzyme in proteome analysis as a potential candidate for this activity. Similarly, the phosphate acetyltransferase and acetate kinase genes, which are considered responsible for acetate formation, were not present in the genome. In P. acidipropionici, a similar function seems to be performed by an ADP forming acetate-CoA ligase gene and its corresponding enzyme was confirmed in the proteome analysis.

CONCLUSIONS

Our data shows that P. acidipropionici has several of the desired features that are required to become a platform for the production of chemical commodities: multiple pathways for efficient feedstock utilization, ability to fix CO2, robustness, and efficient production of propionic acid, a potential precursor for valuable 3-carbon compounds.

Multifaceted attributes of dairy propionibacteria: a review

Dairy propionibacteria are Generally Recognized as Safe (GRAS) status microorganisms which have been traditionally used for the manufacture of Swiss type cheeses. In the last two decades various added features and functionalities have been discovered and developed from these bacteria. Propionibacteria are robust organisms with remarkable adaptability to technological and physiological stress conditions. Besides, they also display a multitude of health promoting properties like modulation of gut microbiota, improved gut physiology and immunomodulation suggesting their promising probiotic potential. Propionibacteria produce an interestingly wide range of functional biomolecules like B group vitamins, trehalose, conjugated linoleic acid, propionic acid, bacteriocins, bifidogenic factors etc. These bacteria are thus now being explored for designing novel functional foods as well as for industrial production of nutraceuticals. Growing interest in these bacteria is fueled by the first whole genome sequencing of a Propionibacterium freudenreichii strain providing a platform for better understanding of various pathways and further improvement in related process technologies.

The channel physiology of the skin

During embryonic development, the skin, the largest organ of the human body, and nervous system are both derived from the neuroectoderm. Consequently, several key factors and mechanisms that influence and control central or peripheral nervous system activities are also present and hence involved in various regulatory mechanisms of the skin. Apparently, this is the case for the ion and non-ion selective channels as well. Therefore, in this review, we shall focus on delineating the regulatory roles of the channels in skin physiology and pathophysiology. First, we introduce key cutaneous functions and major characteristics of the channels in question. Then, we systematically detail the involvement of a multitude of channels in such skin processes (e.g. skin barrier formation, maintenance, and repair, immune mechanisms, exocrine secretion) which are mostly defined by cutaneous non-neuronal cell populations. Finally, we close by summarizing data suggesting that selected channels are also involved in skin diseases such as e.g. atopic dermatitis, psoriasis, non-melanoma cancers and malignant melanoma, genetic and autoimmune diseases, etc., as well as in skin ageing.

Transcription analysis of a lantibiotic gene cluster from Bifidobacterium longum DJO10A

Bifidobacterium longum DJO10A was previously demonstrated to produce a lantibiotic, but only during growth on agar media. To evaluate the feasibility of production of this lantibiotic in broth media, a transcription analysis of the lanA gene was undertaken. Comparative microarray analysis of broth and agar cultures of B. longum DJO10A revealed that the lantibiotic production, modification, transport/peptidase, and immunity genes were significantly upregulated in agar cultures, while the two-component regulatory genes were expressed equally under both conditions. This suggested that the signal transduction regulatory system should function in broth cultures. Real-time PCR and Northern hybridization confirmed that lanA gene expression was significantly repressed in broth cultures. A crude lantibiotic preparation from an agar-grown culture was obtained, and its antimicrobial spectrum analysis revealed a broad inhibition range. Addition of this extract to broth cultures of B. longum DJO10A induced lanA gene expression in a dose-dependent fashion. Subinoculation using >10% of an induced broth culture maintained lanA expression. The expression of lanA was log-phase specific, being significantly downregulated in stationary phase. Transcription start analysis of lanA revealed a 284-bp 5' untranslated region, which was proposed to be involved in repression of transcription, while an inverted repeat structure located at bp -75 relative to the transcription start was strategically located to likely function as a binding site for the two-component response regulator. Understanding the transcription regulation of this lanA gene is the first step toward enabling production of this novel and potentially interesting lantibiotic in broth cultures.

Skin microbiota: a source of disease or defence?

Microbes found on the skin are usually regarded as pathogens, potential pathogens or innocuous symbiotic organisms. Advances in microbiology and immunology are revising our understanding of the molecular mechanisms of microbial virulence and the specific events involved in the host-microbe interaction. Current data contradict some historical classifications of cutaneous microbiota and suggest that these organisms may protect the host, defining them not as simple symbiotic microbes but rather as mutualistic. This review will summarize current information on bacterial skin flora including Staphylococcus, Corynebacterium, Propionibacterium, Streptococcus and Pseudomonas. Specifically, the review will discuss our current understanding of the cutaneous microbiota as well as shifting paradigms in the interpretation of the roles microbes play in skin health and disease.

Anatomy of the replication origin of plasmid ColE2-P9

The plasmid ColE2-P9 origin is a 32-bp region which is specifically recognized by the plasmid-specified Rep protein to initiate DNA replication. We analyzed the structural and functional organization of the ColE2 origin by using various derivatives carrying deletions and single-base-pair substitutions. The origin may be divided into three subregions: subregion I, which is important for stable binding of the Rep protein; subregion II, which is important for binding of the Rep protein and for initiation of DNA replication; and subregion III, which is important for DNA replication but apparently not for binding of the Rep protein. The Rep protein might recognize three specific DNA elements in subregions I and II. The relative transformation frequency of the autonomously replicating plasmids carrying deletions in subregion I is lower, and nevertheless the copy numbers of these plasmids in host bacteria are higher than those of the wild-type plasmid. Efficient and stable binding of the Rep protein to the origin might be important for the replication efficiency to be at the normal (low) level. Subregion II might be essential for interaction with the catalytic domain of the Rep protein for primer RNA synthesis. The 8-bp sequence across the border of subregions II and III, including the primer sequence, is conserved in the (putative) origins of many plasmids, the putative Rep proteins of which are related to the ColE2-P9 Rep protein. Subregion III might be required for a step that is necessary after Rep protein binding has taken place.

Complete sequencing and diversity analysis of the enterotoxin-encoding plasmids in Clostridium perfringens type A non-food-borne human gastrointestinal disease isolates

Enterotoxin-producing Clostridium perfringens type A isolates are an important cause of food poisoning and non-food-borne human gastrointestinal diseases, e.g., sporadic diarrhea (SPOR) and antibiotic-associated diarrhea (AAD). The enterotoxin gene (cpe) is usually chromosomal in food poisoning isolates but plasmid-borne in AAD/SPOR isolates. Previous studies determined that type A SPOR isolate F5603 has a plasmid (pCPF5603) carrying cpe, IS1151, and the beta2 toxin gene (cpb2), while type A SPOR isolate F4969 has a plasmid (pCPF4969) lacking cpb2 and IS1151 but carrying cpe and IS1470-like sequences. By completely sequencing these two cpe plasmids, the current study identified pCPF5603 as a 75.3-kb plasmid carrying 73 open reading frames (ORFs) and pCPF4969 as a 70.5-kb plasmid carrying 62 ORFs. These plasmids share an approximately 35-kb conserved region that potentially encodes virulence factors and carries ORFs found on the conjugative transposon Tn916. The 34.5-kb pCPF4969 variable region contains ORFs that putatively encode two bacteriocins and a two-component regulator similar to VirR/VirS, while the approximately 43.6-kb pCPF5603 variable region contains a functional cpb2 gene and several metabolic genes. Diversity studies indicated that other type A plasmid cpe+/IS1151 SPOR/AAD isolates carry a pCPF5603-like plasmid, while other type A plasmid cpe+/IS1470-like SPOR/AAD isolates carry a pCPF4969-like plasmid. Tn916-related ORFs similar to those in pCPF4969 (known to transfer conjugatively) were detected in the cpe plasmids of other type A SPOR/AAD isolates, as well as in representative C. perfringens type B to D isolates carrying other virulence plasmids, possibly suggesting that most or all C. perfringens virulence plasmids transfer conjugatively.

Heterologous production of antimicrobial peptides in Propionibacterium freudenreichii

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 (P4) 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 P4 and Ppamp promoters directed constitutive gene expression, and activity of both promoters was enhanced by elements upstream of the promoter core region.

Molecular and genetic characterization of propionicin F, a bacteriocin from Propionibacterium freudenreichii

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.

Prevalence of the genes encoding propionicin T1 and protease-activated antimicrobial peptide and their expression in classical propionibacteria

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.

Comparative genomics identified two conserved DNA modules in a corynebacterial plasmid family present in clinical isolates of the opportunistic human pathogen Corynebacterium jeikeium

Investigation of 62 clinical isolates of the opportunistic human pathogen Corynebacterium jeikeium revealed that 17 possessed plasmids ranging in size from 7.6 to 14.9 kb. The plasmids formed four groups on DNA restriction analysis. The complete nucleotide sequence of a representative from each group (pK43, pK64, pCJ84, and pB85766) was subsequently determined. Additionally, two plasmids (pCo455 and pCo420) were shown to be derivatives of pK43 and pK64 carrying insertion sequences of the IS3 family. Comparative genomics identified a conserved plasmid backbone consisting of two distinct DNA modules. Conserved motifs in the parAB-repA module indicated that the sequenced plasmids from C. jeikeium are new members of the pNG2 family. Recombinant derivatives of pK43 were shown to replicate in the soil bacterium Corynebacterium glutamicum and in the human pathogen Corynebacterium diphtheriae. The second plasmid module most likely encodes a novel type of DNA invertase. The respective gene is flanked by highly conserved 112-bp inverted repeats. All plasmids are 'loaded' with a characteristic set of genes encoding products of unknown function. Plasmids indistinguishable from pK43 by DNA restriction analysis were identified in different C. jeikeium strains, which revealed 16S-23S rDNA spacer length polymorphisms and specific antibiotic susceptibility profiles, implying a wide dissemination of the plasmid in clinical isolates of C. jeikeium.

Characterization of thoeniicin 447, a bacteriocin isolated from Propionibacterium thoenii strain 447

Fifteen strains of propionibacteria, isolated from dairy products, were screened for the production of bacteriocins. Propionibacterium thoenii 447 produced an antimicrobial peptide, thoeniicin 447, which acted bactericidal against Lactobacillus delbrueckii subsp. bulgaricus and bacteriostatic against Propionibacterium acnes. Thoeniicin 447 remained active after 15 min at 100 degrees C and after 30 min of incubation at pH 1-10. The peptide was inactivated when treated with pepsin, pronase, alpha-chymotrypsin, trypsin and proteinase K. Optimal bacteriocin production was detected during late exponential growth. The peptide was partially purified by ammonium sulfate precipitation, followed by SP-Sepharose cation exchange chromatography. The estimated size of thoeniicin 447, according to tricine-SDS-PAGE, is 6 kDa. Based on DNA sequencing, the mature peptide is 7130.20 Da in size and homologous to propionicin T1, produced by P. thoenii strain 419 (=NCFB 568(T)). Strain 447 is phenotypically different from strain 419 and belongs to a separate ribotype cluster. To our knowledge, this is the first report of a bacteriocin from a Propionibacterium species active against P. acnes.

Two different propionicins produced by Propionibacterium thoenii P-127

The bacteriocin GBZ-1 was purified from the growth media of Propionibacterium thoenii P-127 and was found to have a molecular weight of 6000Da. P. thoenii P-127 also known as the producer of the bacteriocin PLG-1 (MW 10kDa). Under specific growth conditions, on semi-solid media, P. thoenii P-127 produced both PLG-1 and GBZ-1. The N-terminal of GBZ-1 was microsequenced, the gene was cloned and the DNA sequence was determined and identified. GBZ-1 is highly homologous to a protease-activated antimicrobial peptide (PAMP). In contrast to PAMP, it was purified in its active form and no protease digestion was required for its activation. The survival curve of indicator bacteria Lactobacillus delbrueckii subsp. lactic ATCC 4797 showed two phases. The fast phase of 20min was followed by a slow phase. While bacterial survival was reduced by 2logs during the fast phase, bacterial survival was reduced by additional 3logs up to 200min during the slow phase. GBZ-1 activity was affected by magnesium and its activity was completely abolished at 50mM magnesium chloride. Other divalent cations had no effect on GBZ-1 activity of GBZ-1. To the best of our knowledge this is the first report of a bacterium producing two different bacteriocins under different growth conditions.

An antimicrobial peptide is produced by extracellular processing of a protein from Propionibacterium jensenii

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 approximately 4 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.