Macedocin, a food-grade lantibiotic produced by Streptococcus macedonicus ACA-DC 198

Prebiotic inulin enhances gut microbial metabolism and anti-inflammation in apolipoprotein E4 mice with sex-specific implications

Gut dysbiosis has been identified as a crucial factor of Alzheimer's disease (AD) development for apolipoprotein E4 (APOE4) carriers. Inulin has shown the potential to mitigate dysbiosis. However, it remains unclear whether the dietary response varies depending on sex. In the study, we fed 4-month-old APOE4 mice with inulin for 16 weeks and performed shotgun metagenomic sequencing to determine changes in microbiome diversity, taxonomy, and functional gene pathways. We also formed the same experiments with APOE3 mice to identify whether there are APOE-genotype dependent responses to inulin. We found that APOE4 female mice fed with inulin had restored alpha diversity, significantly reduced Escherichia coli and inflammation-associated pathway responses. However, compared with APOE4 male mice, they had less metabolic responses, including the levels of short-chain fatty acids-producing bacteria and the associated kinases, especially those related to acetate and Erysipelotrichaceae. These diet- and sex- effects were less pronounced in the APOE3 mice, indicating that different APOE variants also play a significant role. The findings provide insights into the higher susceptibility of APOE4 females to AD, potentially due to inefficient energy production, and imply the importance of considering precision nutrition for mitigating dysbiosis and AD risk in the future.

Characterization of TelE, a T7SS LXG Effector Exhibiting a Conserved C-Terminal Glycine Zipper Motif Required for Toxicity

Streptococcus gallolyticus subsp. gallolyticus (SGG) is an opportunistic bacterial pathogen strongly associated with colorectal cancer. Here, through comparative genomics analysis, we demonstrated that the genetic locus encoding the type VIIb secretion system (T7SSb) machinery is uniquely present in SGG in two different arrangements. SGG UCN34 carrying the most prevalent T7SSb genetic arrangement was chosen as the reference strain. To identify the effectors secreted by this secretion system, we inactivated the essC gene encoding the motor of this machinery. A comparison of the proteins secreted by UCN34 wild type and its isogenic ΔessC mutant revealed six T7SSb effector proteins, including the expected WXG effector EsxA and three LXG-containing proteins. In this work, we characterized an LXG-family toxin named herein TelE promoting the loss of membrane integrity. Seven homologs of TelE harboring a conserved glycine zipper motif at the C terminus were identified in different SGG isolates. Scanning mutagenesis of this motif showed that the glycine residue at position 470 was crucial for TelE membrane destabilization activity. TelE activity was antagonized by a small protein TipE belonging to the DUF5085 family. Overall, we report herein a unique SGG T7SSb effector exhibiting a toxic activity against nonimmune bacteria. IMPORTANCE In this study, 38 clinical isolates of Streptococcus gallolyticus subsp. gallolyticus (SGG) were sequenced and a genetic locus encoding the type VIIb secretion system (T7SSb) was found conserved and absent from 16 genomes of the closely related S. gallolyticus subsp. pasteurianus (SGP). The T7SSb is a bona fide pathogenicity island. Here, we report that the model organism SGG strain UCN34 secretes six T7SSb effectors. One of the six effectors named TelE displayed a strong toxicity when overexpressed in Escherichia coli. Our results indicate that TelE is probably a pore-forming toxin whose activity can be antagonized by a specific immunity protein named TipE. Overall, we report a unique toxin-immunity protein pair and our data expand the range of effectors secreted through T7SSb.

Comparison of the Strengths and Weaknesses of Machine Learning Algorithms and Feature Selection on KEGG Database Microbial Gene Pathway Annotation and Its Effects on Reconstructed Network Topology

The development of tools for the annotation of genes from newly sequenced species has not evolved much from homologous alignment to prior annotated species. While the quality of gene annotations continues to decline as we sequence and assemble more evolutionary distant gut microbiome species, machine learning presents a high quality alternative to traditional techniques. In this study, we investigate the relative performance of common classical and nonclassical machine learning algorithms in the problem of gene annotation using human microbiome-associated species genes from the KEGG database. The majority of the ensemble, clustering, and deep learning algorithms that we investigated showed higher prediction accuracy than CD-Hit in predicting partial KEGG function. Motif-based, machine-learning methods of annotation in new species were faster and had higher precision-recall than methods of homologous alignment or orthologous gene clustering. Gradient boosted ensemble methods and neural networks also predicted higher connectivity in reconstructed KEGG pathways, finding twice as many new pathway interactions than blast alignment. The use of motif-based, machine-learning algorithms in annotation software will allow researchers to develop powerful tools to interact with bacterial microbiomes in ways previously unachievable through homologous sequence alignment alone.

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

Nisin A, the prototypical lantibiotic, is an antimicrobial peptide currently utilised as a food preservative, with potential for therapeutic applications. Here, we describe nisin E, a novel nisin variant produced by two Streptococcus equinus strains, APC4007 and APC4008, isolated from sheep milk. Shotgun whole genome sequencing and analysis revealed biosynthetic gene clusters similar to nisin U, with a unique rearrangement of the core peptide encoding gene within the cluster. The 3100.8 Da peptide by MALDI-TOF mass spectrometry, is 75% identical to nisin A, with 10 differences, including 2 deletions: Ser29 and Ile30, and 8 substitutions: Ile4Lys, Gly18Thr, Asn20Pro, Met21Ile, His27Gly, Val32Phe, Ser33Gly, and Lys34Asn. Nisin E producing strains inhibited species of Lactobacillus, Bacillus, and Clostridiodes and were immune to nisin U. Sequence alignment identified putative promoter sequences across the nisin producer genera, allowing for the prediction of genes in Streptococcus to be potentially regulated by nisin. S. equinus pangenome BLAST analyses detected 6 nisin E operons across 44 publicly available genomes. An additional 20 genomes contained a subset of nisin E transport/immunity and regulatory genes (nseFEGRK), without adjacent peptide production genes. These genes suggest that nisin E response mechanisms, distinct from the canonical nisin immunity and resistance operons, are widespread across the S. equinus species. The discovery of this new nisin variant and its immunity determinants in S. equinus suggests a central role for nisin in the competitive nature of the species.

Stability and Activity of the Antimicrobial Peptide Leg1 in Solution and on Meat and Its Optimized Generation from Chickpea Storage Protein

The antimicrobial peptide Leg1 (RIKTVTSFDLPALRFLKL) from chickpea legumin is active against spoilage bacteria, yeast, and mold. The present study tested its effectiveness under food storage conditions and examined options to obtain a food-grade agent. The minimum inhibitory concentration (MIC) of Leg1 against E. coli (62.5 µM) proved stable over seven days at 20 °C or 4 °C. It was not influenced by reduced pH (5.0 vs. 6.8), which is relevant in food such as meat. An incubation temperature of 20 °C vs. 37 °C reduced the MIC to 15.6/7.8 µM against E. coli/B. subtilis. With a minimum bactericidal concentration in meat of 125/15.6 µM against E. coli/B. subtilis, Leg1 is equivalently effective as nisin and 5000–82,000 times more active than sodium benzoate, potassium sorbate, or sodium nitrite. Replacing the counter-ion trifluoroacetate derived from peptide synthesis by the more natural alternatives acetate or chloride did not impair the activity of Leg1. As an alternative to chemical synthesis, an optimized protocol for chymotryptic hydrolysis was developed, increasing the yield from chickpea legumin by a factor of 30 compared to the standard procedure. The present results indicate that food-grade Leg1 could possibly be applicable for food preservation.

Application of bacteriocins in food preservation and infectious disease treatment for humans and livestock: a review

Infectious diseases caused by bacteria that can be transmitted via food, livestock and humans are always a concern to the public, as majority of them may cause severe illnesses and death. Antibacterial agents have been investigated for the treatment of bacterial infections. Antibiotics are the most successful antibacterial agents that have been used widely for decades to ease human pain caused by bacterial infections. Nevertheless, the emergence of antibiotic-resistant bacteria has raised awareness amongst public about the downside of using antibiotics. The threat of antibiotic resistance to global health, food security and development has been emphasized by the World Health Organization (WHO), and research studies have been focused on alternative antimicrobial agents. Bacteriocin, a natural antimicrobial peptide, has been chosen to replace antibiotics for its application in food preservation and infectious disease treatment for livestock and humans, as it is less toxic.

Killing or inhibition actions of (a) antibiotics and (b) bacteriocin on gut microbiota.

Dietary inclusion of Peptiva, a peptide-based feed additive, can accelerate the maturation of the fecal bacterial microbiome in weaned pigs

Background

Weaning is one of the most critical transition stages of the swine production cycle, as the piglet gut physiology and microbiome need to rapidly adapt to changes in diet and environmental conditions. Based on their potential for producing a vast array of bioactive molecules, peptide formulations represent a largely untapped source of compounds that could be developed into feed additives to benefit animal health and nutrition. In this context, a commercial-scale nursery trial was performed to evaluate the impact of low inclusion of a peptide-based feed additive (Peptiva, Vitech Bio-Chem Corporation) on the performance and fecal microbiome of weaned pigs.

Results

While no significant differences in body weight, daily gain, daily feed intake nor gain:feed were observed between control and treatment animals (P > 0.05), an effect of Peptiva on the fecal bacterial composition of weaned pigs was observed. The first main observation was that the fecal bacterial profiles from pigs fed Control-Phase II and Control Phase III diets were found to be very distinct, suggesting that a transition or succession stage had occurred between the two phases. Lactobacilli, represented by four main OTUs (Ssd-00002, Ssd-00019, Ssd-00025, and Ssd-00053), were more abundant at the end of Phase II (P < 0.05), while Streptococci, mostly represented by OTUs Ssd-00039 and Ssd-00048, were in higher abundance at the end of Phase III (P < 0.05). Secondly, the fecal bacterial composition from pigs fed Peptiva Phase II diets showed similarities to both Control-Phase II and Control Phase III samples, while there was no difference in fecal bacterial composition between Control-Phase III and Peptiva Phase III samples. For instance, OTUs Ssd-00019,and Ssd-00053 were in lower abundance in Peptiva Phase II samples compared to Control Phase II (P < 0.05), but no significant difference was observed in the abundance of these two OTUs when comparing Peptiva Phase II to Control Phase III (P > 0.05).

Conclusions

Together, these results suggest that Peptiva can modulate the composition of the swine microbiome during a specific window of the nursery stage, potentially by accelerating its maturation.

Antibiotics: From the Beginning to the Future: Part 2

We read, write, and discuss the option of adding new agents to the armamentarium of antibiotic therapy very frequently. However, the past and present has taught us that resistance is likely to develop to any and all kinds of antibiotics. Here we start with an overview of potential future antibiotics from novel sources and targets that may circumvent most known resistance mechanisms. The other future options for antibiotic discovery include antibiotic hybridization, harvesting, and modifying natural antimicrobial peptides from eukaryote and prokaryote organisms. Non bacteriostatic and bactericidal agents that have the potential of becoming therapeutic agents include bacterial attachment inhibitors, bacteriophages, and live microbial vectors. In this review, we have incorporated all the possible avenues that might be useful in the future. However, none is more important than relearning the judicious use of antibiotics based on microbiology, pharmacology, and genetics.

Virgicin, a novel lanthipeptide from Virgibacillus sp. strain AK90 exhibits inhibitory activity against Gram-positive bacteria

There is a significant increase in the discovery of new antimicrobial compounds in recent past to combat drug resistant pathogens. Members of the genus Bacillus and related genera have been screened extensively due to their ability to produce wide range of antimicrobial compounds. In this study, we have isolated and characterized a new antimicrobial peptide from a marine bacterium identified as Virgibacillus species. The low molecular mass and stability of the antimicrobial substance pointed towards the bacteriocinogenic nature of the compound. The RAST analysis of genome sequence showed presence of a putative bacteriocin biosynthetic cluster containing genes necessary for synthesis of a lanthipeptide. Translated amino acid sequence of mature C-terminal propeptide showed identity with salivaricin A (52.2%) and lacticin A (33.3%). Accordingly, the mass (2417 Da) obtained by MALDI analysis was in agreement with posttranslational modifications of the leader peptide to yield three methyl lanthionine rings and a disulfide bond between two free cysteine residues. The lanthipeptide was named as virgicin, which selectively inhibited the growth of Gram-positive bacteria and biofilm formation by Enterococcus faecalis. Inhibition of biofilm formation by E. faecalis was also observed in in vitro model experiments using hydroxyapatite discs. Thus, virgicin appears to be a promising new bacteriocin to control oral biofilm formation by selective pathogens.

Ocins for Food Safety

The food industry produces highly perishable products. Food spoilage represents a severe problem for food manufacturers. Therefore, it is important to identify effective preservation solutions to prevent food spoilage. Ocins (e.g., bacteriocins, lactocins, and enterocins) are antibacterial proteins synthesized by bacteria that destroy or suppress the growth of related or unrelated bacterial strains. Ocins represent a promising strategy for food preservation, because of their antagonist effects toward food spoilage microorganisms, high potency, and low toxicity. Additionally, they can be bioengineered. The most common and commercially available ocins are nisin, plantaracin, sakacin P, and pediocin. Several ocins have been characterized and studied biochemically and genetically; however, their structure-function relationship, biosynthesis, and mechanism of action are not understood. This narrative review focuses primarily on ocins and their relevance to the food industry to help prevent food spoilage. In particular, the applications and limitations of ocins in the food industry are highlighted.

Streptococcus macedonicus strains isolated from traditional fermented milks: resistance to gastrointestinal environment and adhesion ability

In this study, Streptococcus macedonicus (S. macedonicus) strains were identified from Algerian traditional fermented milks (Lben and Rayeb). Important prerequisites of probiotic interest such as acidity, bile salts tolerance, and adhesion ability to epithelial cells were investigated. A combination of phenotypic (ability to grow on Bile Esculin Azide medium, BEA; on high salt content medium NaCl 6.5%; on alkaline medium pH 9.6) and genotypic approaches (16S rRNA, ITS genes sequencing and MLST technique) allowed to identify four genetically distinct strains of S. macedonicus. These four strains and two references, Streptococcus thermophilus LMD-9 and Lactobacillus rhamnosus GG (LGG), were tested for their capacity to survive at low pH values, and at different concentrations of an equimolar bile salts mixture (BSM). Two different cell lines, Caco-2 TC7 and HT29-MTX, were used for the adhesion study. The results show that S. macedonicus strains selected constitute a distinct genetic entity from the Greek strain S. macedonicus ACA-DC-198. They were able to survive up to pH 3 and could tolerate high concentrations of bile salts (10 mM), unlike LMD-9 and LGG strains. Our strains also display in vitro adhesion similar to the LGG strain on Caco-2 TC7 and higher adhesion than the LMD-9 strain to Caco-2 TC7 and HT29-MTX cell models. This first characterization allows considering S. macedonicus as a potential candidate for possible probiotic effects that need to be investigated.

Persistence of a dominant bovine lineage of group B Streptococcus reveals genomic signatures of host adaptation

Group B Streptococcus (GBS) is a host-generalist species, most notably causing disease in humans and cattle. However, the differential adaptation of GBS to its two main hosts, and the risk of animal to human infection remain poorly understood. Despite improvements in control measures across Europe, GBS is still one of the main causative agents of bovine mastitis in Portugal. Here, by whole-genome analysis of 150 bovine GBS isolates we discovered that a single CC61 clone is spreading throughout Portuguese herds since at least the early 1990s, having virtually replaced the previous GBS population. Mutations within an iron/manganese transporter were independently acquired by all of the CC61 isolates, underlining a key adaptive strategy to persist in the bovine host. Lateral transfer of bacteriocin production and antibiotic resistance genes also underscored the contribution of the microbial ecology and genetic pool within the bovine udder environment to the success of this clone. Compared to strains of human origin, GBS evolves twice as fast in bovines and undergoes recurrent pseudogenizations of human-adapted traits. Our work provides new insights into the potentially irreversible adaptation of GBS to the bovine environment.

Bacteriocin production and different strategies for their recovery and purification

Bacteriocins from lactic acid bacteria (LAB) are a diverse group of antimicrobial proteins/peptides, offering potential as biopreservatives, and exhibit a broad spectrum of antimicrobial activity at low concentrations along with thermal as well as pH stability in foods. High bacteriocin production usually occurs in complex media. However, such media are expensive for an economical production process. For effective use of bacteriocins as food biopreservatives, there is a need to have heat-stable wide spectrum bacteriocins produced with high-specific activity in food-grade medium. The main hurdles concerning the application of bacteriocins as food biopreservatives is their low yield in food-grade medium and time-consuming, expensive purification processes, which are suitable at laboratory scale but not at industrial scale. So, the present review focuses on the bacteriocins production using complex and food-grade media, which mainly emphasizes on the bacteriocin producer strains, media used, different production systems used and effect of different fermentation conditions on the bacteriocin production. In addition, this review emphasizes the purification processes designed for efficient recovery of bacteriocins at small and large scale.

Bacteriocins: Novel Solutions to Age Old Spore-Related Problems?

Bacteriocins are ribosomally synthesized antimicrobial peptides produced by bacteria, which have the ability to kill or inhibit other bacteria. Many bacteriocins are produced by food grade lactic acid bacteria (LAB). Indeed, the prototypic bacteriocin, nisin, is produced by Lactococcus lactis, and is licensed in over 50 countries. With consumers becoming more concerned about the levels of chemical preservatives present in food, bacteriocins offer an alternative, more natural approach, while ensuring both food safety and product shelf life. Bacteriocins also show additive/synergistic effects when used in combination with other treatments, such as heating, high pressure, organic compounds, and as part of food packaging. These features are particularly attractive from the perspective of controlling sporeforming bacteria. Bacterial spores are common contaminants of food products, and their outgrowth may cause food spoilage or food-borne illness. They are of particular concern to the food industry due to their thermal and chemical resistance in their dormant state. However, when spores germinate they lose the majority of their resistance traits, making them susceptible to a variety of food processing treatments. Bacteriocins represent one potential treatment as they may inhibit spores in the post-germination/outgrowth phase of the spore cycle. Spore eradication and control in food is critical, as they are able to spoil and in certain cases compromise the safety of food by producing dangerous toxins. Thus, understanding the mechanisms by which bacteriocins exert their sporostatic/sporicidal activity against bacterial spores will ultimately facilitate their optimal use in food. This review will focus on the use of bacteriocins alone, or in combination with other innovative processing methods to control spores in food, the current knowledge and gaps therein with regard to bacteriocin-spore interactions and discuss future research approaches to enable spores to be more effectively targeted by bacteriocins in food settings.

Something Old and Something New: An Update on the Amazing Repertoire of Bacteriocins Produced by Streptococcus salivarius

Streptococcus salivarius has an exclusive and intimate association with humans. We are its sole natural host, and its contribution to the relationship appears overwhelmingly benevolent. Beautifully adapted to its preferred habitat, the human tongue, it only rarely ventures far from this location in the healthy host and indeed appears ill-equipped to become invasive due to a scarcity of virulence attributes. We consider that its strategically advantageous lingual location and numerical predominance allow S. salivarius to carry out a population surveillance and modulation role within the oral microbiota. Some strains are armed with complex arrays of targeted antibiotic weaponry, much of which belongs to the lantibiotic class of bacteriocins and a key to their ability to assemble and utilize this armament is their possession of transmissible multi-bacteriocin-encoding megaplasmid DNA. This review traces the origins of research into S. salivarius bacteriocins and bacteriocin-like inhibitory substances, showcases some of the inhibitory activities that we currently have knowledge of, and speculates about potential directions for ongoing investigation and probiotic application of this previously under-rated human commensal.

Characterization of the Antimicrobial Peptide Penisin, a Class Ia Novel Lantibiotic from Paenibacillus sp. Strain A3

Attempts to isolate novel antimicrobial peptides from microbial sources have been on the rise recently, despite their low efficacy in therapeutic applications. Here, we report identification and characterization of a new efficient antimicrobial peptide from a bacterial strain designated A3 that exhibited highest identity with Paenibacillus ehimensis. Upon purification and subsequent molecular characterization of the antimicrobial peptide, referred to as penisin, we found the peptide to be a bacteriocin-like peptide. Consistent with these results, RAST analysis of the entire genome sequence revealed the presence of a lantibiotic gene cluster containing genes necessary for synthesis and maturation of a lantibiotic. While circular dichroism and one-dimension nuclear magnetic resonance experiments confirmed a random coil structure of the peptide, similar to other known lantibiotics, additional biochemical evidence suggests posttranslational modifications of the core peptide yield six thioether cross-links. The deduced amino acid sequence of the putative biosynthetic gene penA showed approximately 74% similarity with elgicin A and 50% similarity with the lantibiotic paenicidin A. Penisin effectively killed methicillin-resistant Staphylococcus aureus (MRSA) and did not exhibit hemolysis activity. Unlike other lantibiotics, it effectively inhibited the growth of Gram-negative bacteria. Furthermore, 80 mg/kg of body weight of penisin significantly reduced bacterial burden in a mouse thigh infection model and protected BALB/c mice in a bacteremia model entailing infection with Staphylococcus aureus MTCC 96, suggesting that it could be a promising new antimicrobial peptide.

Fibrolytic Bacteria Isolated from the Rumen of North American Moose (Alces alces) and Their Use as a Probiotic in Neonatal Lambs

Fibrolytic bacteria were isolated from the rumen of North American moose (Alces alces), which eat a high-fiber diet of woody browse. It was hypothesized that fibrolytic bacteria isolated from the moose rumen could be used as probiotics to improve fiber degradation and animal production. Thirty-one isolates (Bacillus, n = 26; Paenibacillus, n = 1; and Staphylococcus, n = 4) were cultured from moose rumen digesta samples collected in Vermont. Using Sanger sequencing of the 16S rRNA gene, culturing techniques, and optical densities, isolates were identified and screened for biochemical properties important to plant carbohydrate degradation. Five isolates were selected as candidates for use as a probiotic, which was administered daily to neonate lambs for 9 weeks. It was hypothesized that regular administration of a probiotic to improve fibrolysis to neonate animals through weaning would increase the developing rumen bacterial diversity, increase animal production, and allow for long-term colonization of the probiotic species. Neither weight gain nor wool quality was improved in lambs given a probiotic, however, dietary efficiency was increased as evidenced by the reduced feed intake (and rearing costs) without a loss to weight gain. Experimental lambs had a lower acetate to propionate ratio than control lambs, which was previously shown to indicate increased dietary efficiency. Fibrolytic bacteria made up the majority of sequences, mainly Prevotella, Butyrivibrio, and Ruminococcus. While protozoal densities increased over time and were stable, methanogen densities varied greatly in the first six months of life for lambs. This is likely due to the changing diet and bacterial populations in the developing rumen.

Engineered strains of Streptococcus macedonicus towards an osmotic stress resistant phenotype retain their ability to produce the bacteriocin macedocin under hyperosmotic conditions

Streptococcus macedonicus ACA-DC 198 produces the bacteriocin macedocin in milk only under low NaCl concentrations (<1.0%w/v). The thermosensitive plasmid pGh9:ISS1 was employed to generate osmotic stress resistant (osmr) mutants of S. macedonicus. Three osmr mutants showing integration of the vector in unique chromosomal sites were identified and the disrupted loci were characterized. Interestingly, the mutants were able to grow and to produce macedocin at considerably higher concentrations of NaCl compared to the wild-type (up to 4.0%w/v). The production of macedocin under hyperosmotic conditions solely by the osmr mutants was validated by the well diffusion assay and by mass spectrometry analysis. RT-PCR experiments demonstrated that the macedocin biosynthetic regulon was transcribed at high salt concentrations only in the mutants. Mutant osmr3, the most robust mutant, was converted in its markerless derivative (osmr3f). Co-culture of S. macedonicus with spores of Clostridium tyrobutyricum in milk demonstrated that only the osmr3f mutant and not the wild-type inhibited the growth of the spores under hyperosmotic conditions (i.e., 2.5%w/v NaCl) due to the production of macedocin. Our study shows how genetic manipulation of a strain towards a stress resistant phenotype could improve bacteriocin production under conditions of the same stress.

Perspectives on lantibiotic discovery - where have we failed and what improvements are required?

The increasing resistance of bacteria to conventional antimicrobial therapy within both the nosocomial and community environment has enforced the urgent requirement for the discovery of novel agents. This has stimulated increased research efforts within the field of lantibiotic discovery. Lantibiotics are ribosomally synthesised, post-translationally modified antimicrobial peptides that exhibit antimicrobial activity against a range of multi-drug-resistant (MDR) bacteria. The success of these agents as a novel treatment of MDR infections is exemplified by: the clinical development of MU1140 (mutacin 1140) and NAI-107 (microbisporicin), which are in late pre-clinical trials against gram-positive bacteria; NVB302 that has completed Phase I clinical trials for the treatment of Clostridium difficile infections and; duramycin that has completed Phase II clinical trials in the treatment of cystic fibrosis. Despite these potential successes, the traditional method of lantibiotic discovery involving the induction, production and identification is often an inefficient, time-consuming process creating a barrier to the efficient discovery of novel lantibiotics. The introduction of novel and innovative identification methods, including the application of probes and the ability to improve the stability and activity of agents via mutagenesis offer encouraging new areas to explore. The rapid expansion of available genome sequences of a wide variety of bacteria has revealed multiple interesting lantibiotic clusters that have the potential to be effective antimicrobials. However, due to the inefficient expression, screening and production methods currently employed, they are being assessed inefficiently and not rapidly enough to keep up with the ever-increasing demand for new agents.

Genomics, evolution, and molecular epidemiology of the Streptococcus bovis/Streptococcus equinus complex (SBSEC)

The Streptococcus bovis/Streptococcus equinus complex (SBSEC) is a group of human and animal derived streptococci that are commensals (rumen and gastrointestinal tract), opportunistic pathogens or food fermentation associates. The classification of SBSEC has undergone massive changes and currently comprises 7 (sub)species grouped into four branches based on sequences identities: the Streptococcus gallolyticus, the Streptococcus equinus, the Streptococcus infantarius and the Streptococcus alactolyticus branch. In animals, SBSEC are causative agents for ruminal acidosis, potentially laminitis and infective endocarditis (IE). In humans, a strong association was established between bacteraemia, IE and colorectal cancer. Especially the SBSEC-species S. gallolyticus subsp. gallolyticus is an emerging pathogen for IE and prosthetic joint infections. S. gallolyticus subsp. pasteurianus and the S. infantarius branch are further associated with biliary and urinary tract infections. Knowledge on pathogenic mechanisms is so far limited to colonization factors such as pili and biofilm formation. Certain strain variants of S. gallolyticus subsp. macedonicus and S. infantarius subsp. infantarius are associated with traditional dairy and plant-based food fermentations and display traits suggesting safety. However, due to their close relationship to virulent strains, their use in food fermentation has to be critically assessed. Additionally, implementing accurate and up-to-date taxonomy is critical to enable appropriate treatment of patients and risk assessment of species and strains via recently developed multilocus sequence typing schemes to enable comparative global epidemiology. Comparative genomics revealed that SBSEC strains harbour genomics islands (GI) that seem acquired from other streptococci by horizontal gene transfer. In case of virulent strains these GI frequently encode putative virulence factors, in strains from food fermentation the GI encode functions that are pivotal for strain performance during fermentation. Comparative genomics is a powerful tool to identify acquired pathogenic functions, but there is still an urgent need for more physiological and epidemiological data to understand SBSEC-specific traits.

Comparative genomics of the dairy isolate Streptococcus macedonicus ACA-DC 198 against related members of the Streptococcus bovis/Streptococcus equinus complex

Background

Within the genus Streptococcus, only Streptococcus thermophilus is used as a starter culture in food fermentations. Streptococcus macedonicus though, which belongs to the Streptococcus bovis/Streptococcus equinus complex (SBSEC), is also frequently isolated from fermented foods mainly of dairy origin. Members of the SBSEC have been implicated in human endocarditis and colon cancer. Here we compare the genome sequence of the dairy isolate S. macedonicus ACA-DC 198 to the other SBSEC genomes in order to assess in silico its potential adaptation to milk and its pathogenicity status.

Results

Despite the fact that the SBSEC species were found tightly related based on whole genome phylogeny of streptococci, two distinct patterns of evolution were identified among them. Streptococcus macedonicus, Streptococcus infantarius CJ18 and Streptococcus pasteurianus ATCC 43144 seem to have undergone reductive evolution resulting in significantly diminished genome sizes and increased percentages of potential pseudogenes when compared to Streptococcus gallolyticus subsp. gallolyticus. In addition, the three species seem to have lost genes for catabolizing complex plant carbohydrates and for detoxifying toxic substances previously linked to the ability of S. gallolyticus to survive in the rumen. Analysis of the S. macedonicus genome revealed features that could support adaptation to milk, including an extra gene cluster for lactose and galactose metabolism, a proteolytic system for casein hydrolysis, auxotrophy for several vitamins, an increased ability to resist bacteriophages and horizontal gene transfer events with the dairy Lactococcus lactis and S. thermophilus as potential donors. In addition, S. macedonicus lacks several pathogenicity-related genes found in S. gallolyticus. For example, S. macedonicus has retained only one (i.e. the pil3) of the three pilus gene clusters which may mediate the binding of S. gallolyticus to the extracellular matrix. Unexpectedly, similar findings were obtained not only for the dairy S. infantarius CJ18, but also for the blood isolate S. pasteurianus ATCC 43144.

Conclusions

Our whole genome analyses suggest traits of adaptation of S. macedonicus to the nutrient-rich dairy environment. During this process the bacterium gained genes presumably important for this new ecological niche. Finally, S. macedonicus carries a reduced number of putative SBSEC virulence factors, which suggests a diminished pathogenic potential.

The complex microbiota of raw milk

Here, we review what is known about the microorganisms present in raw milk, including milk from cows, sheep, goats and humans. Milk, due to its high nutritional content, can support a rich microbiota. These microorganisms enter milk from a variety of sources and, once in milk, can play a number of roles, such as facilitating dairy fermentations (e.g. Lactococcus, Lactobacillus, Streptococcus, Propionibacterium and fungal populations), causing spoilage (e.g. Pseudomonas, Clostridium, Bacillus and other spore-forming or thermoduric microorganisms), promoting health (e.g. lactobacilli and bifidobacteria) or causing disease (e.g. Listeria, Salmonella, Escherichia coli, Campylobacter and mycotoxin-producing fungi). There is also concern that the presence of antibiotic residues in milk leads to the development of resistance, particularly among pathogenic bacteria. Here, we comprehensively review these topics, while comparing the approaches, both culture-dependent and culture-independent, which can be taken to investigate the microbial composition of milk.

Comparative genome analysis of Streptococcus infantarius subsp. infantarius CJ18, an African fermented camel milk isolate with adaptations to dairy environment

Background

Streptococcus infantarius subsp. infantarius (Sii) belongs to the Streptococcus bovis/Streptococcus equinus complex associated with several human and animal infections. Sii is a predominant bacterium in spontaneously fermented milk products in Africa. The genome sequence of Sii strain CJ18 was compared with that of other Streptococcus species to identify dairy adaptations including genome decay such as in Streptococcus thermophilus, traits for its competitiveness in spontaneous milk fermentation and to assess potential health risks for consumers.

Results

The genome of Sii CJ18 harbors several unique regions in comparison to Sii ATCC BAA-102^T, among others an enlarged exo- and capsular polysaccharide operon; Streptococcus thermophilus-associated genes; a region containing metabolic and hypothetical genes mostly unique to CJ18 and the dairy isolate Streptococcus gallolyticus subsp. macedonicus; and a second oligopeptide transport operon. Dairy adaptations in CJ18 are reflected by a high percentage of pseudogenes (4.9%) representing genome decay which includes the inactivation of the lactose phosphotransferase system (lacIIABC) by multiple transposases integration. The presence of lacS and lacZ genes is the major dairy adaptation affecting lactose metabolism pathways also due to the disruption of lacIIABC.

We constructed mutant strains of lacS, lacZ and lacIIABC and analyzed the resulting strains of CJ18 to confirm the redirection of lactose metabolism via LacS and LacZ.

Natural competence genes are conserved in both Sii strains, but CJ18 contains a lower number of CRISPR spacers which indicates a reduced defense capability against alien DNA. No classical streptococcal virulence factors were detected in both Sii strains apart from those involved in adhesion which should be considered niche factors. Sii-specific virulence factors are not described. Several Sii-specific regions encoding uncharacterized proteins provide new leads for virulence analyses and investigation of the unclear association of dairy and clinical Sii with human diseases.

Conclusions

The genome of the African dairy isolate Sii CJ18 clearly differs from the human isolate ATCC BAA-102^T. CJ18 possesses a high natural competence predisposition likely explaining the enlarged genome. Metabolic adaptations to the dairy environment are evident and especially lactose uptake corresponds to S. thermophilus. Genome decay is not as advanced as in S. thermophilus (10-19%) possibly due to a shorter history in dairy fermentations.

Incidence of Bacteriocins Produced by Food-Related Lactic Acid Bacteria Active towards Oral Pathogens

In the present study we investigated the incidence of bacteriocins produced by 236 lactic acid bacteria (LAB) food isolates against pathogenic or opportunistic pathogenic oral bacteria. This set of LAB contained several strains (≥17%) producing bacteriocins active against food-related bacteria. Interestingly only Streptococcus macedonicus ACA-DC 198 was able to inhibit the growth of Streptococcus oralis, Streptococcus sanguinis and Streptococcus gordonii, while Lactobacillus fermentum ACA-DC 179 and Lactobacillus plantarun ACA-DC 269 produced bacteriocins solely against Streptococcus oralis. Thus, the percentage of strains that were found to produce bacteriocins against oral bacteria was ~1.3%. The rarity of bacteriocins active against oral LAB pathogens produced by food-related LAB was unexpected given their close phylogenetic relationship. Nevertheless, when tested in inhibition assays, the potency of the bacteriocin(s) of S. macedonicus ACA-DC 198 against the three oral streptococci was high. Fourier-transform infrared spectroscopy combined with principal component analysis revealed that exposure of the target cells to the antimicrobial compounds caused major alterations of key cellular constituents. Our findings indicate that bacteriocins produced by food-related LAB against oral LAB may be rare, but deserve further investigation since, when discovered, they can be effective antimicrobials.

Bacteriocin PJ4 active against enteric pathogen produced by Lactobacillus helveticus PJ4 isolated from gut microflora of wistar rat (Rattus norvegicus): partial purification and characterization of bacteriocin

The increase of multidrug-resistant pathogens and the restriction on the use antibiotics due to its side effects have drawn attention to the search for possible alternatives. Bacteriocins are small antimicrobial peptides produced by numerous bacteria. Much interest has been focused on bacteriocins because they exhibit inhibitory activity against pathogens. Lactic acid bacteria possess the ability to synthesize antimicrobial compounds (like bacteriocin) during their growth. In this study, an antibacterial substance (bacteriocin PJ4) produced by Lactobacillus helveticus PJ4, isolated from rat gut microflora, was identified as bacteriocin. It was effective against wide assay of both Gram-positive and Gram-negative bacteria involved in various diseases, including Escherichia coli, Bacillus subtilis, Pseudomonas aeruginosa, Enterococcus faecalis, and Staphylococcus aureus. The antimicrobial peptide was relatively heat-resistant and also active over a wide pH range of 2-10. It has been partially purified to homogeneity using ammonium sulfate precipitation and size exclusion chromatography and checked on reverse-phase high-performance liquid chromatography. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of bacteriocin PJ4 purified through size exclusion chromatography resolved ~6.5 kDa protein with bacteriocin activity. The peptide is inactivated by proteolytic enzymes, trypsin, and lipase but not when treated with catalase, α-amylase, and pepsin. It showed a bactericidal mode of action against the indicator strains E. coli MTCC443, Lactobacillus casei MTCC1423, and E. faecalis DT48. Such characteristics indicate that this bacteriocin may be a potential candidate for alternative agents to control important pathogens.

Intraguild predation provides a selection mechanism for bacterial antagonistic compounds

Bacteriocins are bacterial proteinaceous toxins with bacteriostatic or bacteriocidal activity towards other bacteria. The current theory on their biological role concerns especially colicins, with underlying social interactions described as an example of spite. This leads to a rock-paper-scissors game between colicin producers and sensitive and resistant variants. The generality of this type of selection mechanism has previously been challenged with lactic acid bacterial (LAB) bacteriocins as an example. In the natural environment of LAB, batch cultures are the norm opposed to the natural habitats of Escherichia coli where continuous cultures are prevailing. This implies that fitness for LAB, to a large degree, is related to survival rates (bottleneck situations) rather than to growth rates. We suggest that the biological role of LAB bacteriocins is to enhance survival in the stationary growth phase by securing a supply of nutrients from lysed target cells. Thus, this social interaction is an example of selfishness rather than of spite. Specifically, it fits into an ecological model known as intraguild predation (IGP), which is a combination of competition and predation where the predator (LAB bacteriocin producer) and prey (bacteriocin susceptible bacteria) share similar and often limited resources. We hypothesize that IGP may be a common phenomenon promoting microbial production of antagonistic compounds.

Salivaricin G32, a Homolog of the Prototype Streptococcus pyogenes Nisin-Like Lantibiotic SA-FF22, Produced by the Commensal Species Streptococcus salivarius

Salivaricin G32, a 2667 Da novel member of the SA-FF22 cluster of lantibiotics, has been purified and characterized from Streptococcus salivarius strain G32. The inhibitory peptide differs from the Streptococcus pyogenes—produced SA-FF22 in the absence of lysine in position 2. The salivaricin G32 locus was widely distributed in BLIS-producing S. salivarius, with 6 (23%) of 26 strains PCR-positive for the structural gene, slnA. As for most other lantibiotics produced by S. salivarius, the salivaricin G32 locus can be megaplasmid encoded. Another member of the SA-FF22 family was detected in two Streptococcus dysgalactiae of bovine origin, an observation supportive of widespread distribution of this lantibiotic within the genus Streptococcus. Since the inhibitory spectrum of salivaricin G32 includes Streptococcus pyogenes, its production by S. salivarius, either as a member of the normal oral microflora or as a commercial probiotic, could serve to enhance protection of the human host against S. pyogenes infection.

Entianin, a novel subtilin-like lantibiotic from Bacillus subtilis subsp. spizizenii DSM 15029T with high antimicrobial activity

Lantibiotics, such as nisin and subtilin, are lanthionine-containing peptides that exhibit antimicrobial as well as pheromone-like autoinducing activity. Autoinduction is specific for each lantibiotic, and reporter systems for nisin and subtilin autoinduction are available. In this report, we used the previously reported subtilin autoinduction bioassay in combination with mass spectrometric analyses to identify the novel subtilin-like lantibiotic entianin from Bacillus subtilis subsp. spizizenii DSM 15029(T). Linearization of entianin using Raney nickel-catalyzed reductive cleavage enabled, for the first time, the use of tandem mass spectrometry for the fast and efficient determination of an entire lantibiotic primary structure, including posttranslational modifications. The amino acid sequence determined was verified by DNA sequencing of the etnS structural gene, which confirmed that entianin differs from subtilin at 3 amino acid positions. In contrast to B. subtilis ATCC 6633, which produces only small amounts of unsuccinylated subtilin, B. subtilis DSM 15029(T) secretes considerable amounts of unsuccinylated entianin. Entianin was very active against several Gram-positive pathogens, such as Staphylococcus aureus and Enterococcus faecalis. The growth-inhibiting activity of succinylated entianin (S-entianin) was much lower than that of unsuccinylated entianin: a 40-fold higher concentration was required for inhibition. For succinylated subtilin (S-subtilin), a concentration 100-fold higher than that of unsuccinylated entianin was required to inhibit the growth of a B. subtilis test strain. This finding was in accordance with a strongly reduced sensing of cellular envelope stress provided by S-entianin relative to that of entianin. Remarkably, S-entianin and S-subtilin showed considerable autoinduction activity, clearly demonstrating that autoinduction and antibiotic activity underlie different molecular mechanisms.

Bacteriocins - exploring alternatives to antibiotics in mastitis treatment

Mastitis is considered to be the most costly disease affecting the dairy industry. Management strategies involve the extensive use of antibiotics to treat and prevent this disease. Prophylactic dosages of antibiotics used in mastitis control programmes could select for strains with resistance to antibiotics. In addition, a strong drive towards reducing antibiotic residues in animal food products has lead to research in finding alternative antimicrobial agents. In this review we have focus on the pathogenesis of the mastitis in dairy cows, existing antibiotic treatments and possible alternative for application of bacteriocins from lactic acid bacteria in the treatment and prevention of this disease.

Mode of action and In Vitro susceptibility of mastitis pathogens to macedocin ST91KM and preparation of a teat seal containing the bacteriocin

Mastitis is considered to be the most economically costly disease affecting the dairy industry. Regular dosage of animals with antibiotics, including use of prophylactic concentrations, may select for resistant strains. The purpose of this study was to determine the mode of action of a new bacteriocin (macedocin ST91KM), to evaluate the antimicrobial resistance of mastitis pathogens to antibiotics commonly used in treatment remedies, and to introduce the possible use of an alternative antimicrobial agent. The bacteriocin macedocin ST91KM, produced by Streptococcus gallolyticus subsp. macedonicus ST91KM, is bactericidal to Streptococcus agalactiae, Streptococcus dysgalactiae, Streptococcus uberis and Staphylococcus aureus associated with mastitis infections, including strains resistant to methicillin and oxacillin. Sensitive cells were deformed and secreted nucleotides, K(+) and β-galactosidase when exposed to macedocin ST91KM. Adsorption of the peptide to target cells decreased in the presence of solvents, suggesting that receptors on the cell surfaces have lipid moieties. No adsorption was recorded in the presence of MgCl2, KI and Na2CO3, suggesting that ionic strength plays an important role. A teat seal preparation containing macedocin ST91KM effectively released the peptide and inhibited the growth of S. agalactiae. Macedocin ST91KM could form the basis for alternative dry cow therapy to prevent mastitis infections in dairy cows as it is effective against pathogens that display resistance to conventional antibiotic therapy.

Milk protein fragments induce the biosynthesis of macedocin, the lantibiotic produced by Streptococcus macedonicus ACA-DC 198

The aim of the present work was to study the mode of the induction of the biosynthesis of macedocin, the lantibiotic produced by Streptococcus macedonicus ACA-DC 198. Macedocin was produced when the strain was grown in milk but not in MRS or M17 broth. No autoinduction mechanism was observed. Production did not depend on the presence of lactose or galactose in the culture medium or on a coculture of the producer strain with macedocin-sensitive or macedocin-resistant strains. Induction seemed to depend on the presence of one or more heat-stable protein components produced when S. macedonicus ACA-DC 198 was grown in milk. The partial purification of the induction factor was performed by a combination of chromatography methods, and its activity was confirmed by a reverse transcription-PCR approach (RT-PCR). Mass spectrometric (MS) and tandem mass spectrometric (MS/MS) analyses of an induction-active fraction showed the presence of several peptides of low molecular mass corresponding to fragments of alpha(S1)- and beta-casein as well as beta-lactoglobulin. The chemically synthesized alpha(S1)-casein fragment 37-55 (2,253.65 Da) was proven to be able to induce macedocin biosynthesis. This is the first time that milk protein degradation fragments are reported to exhibit a bacteriocin induction activity.

Streptococcal bacteriocins and the case for Streptococcus salivarius as model oral probiotics

Members of the Gram-positive bacterial genus Streptococcus are a diverse collection of species inhabiting many body sites and range from benign, nonpathogenic species to those causing life-threatening infections. The streptococci are also prolific producers of bacteriocins, which are ribosomally synthesized proteinaceous antibiotics that kill or inhibit species closely related to the producer bacterium. With the emergence of bacterial resistance to conventional antibiotics, there is an impetus to discover, and implement, new and preferably ‘natural’ antibiotics to treat or prevent bacterial infections, a niche that bacterial interference therapy mediated by bacteriocins could easily fill. This review focuses on describing the diversity of bacteriocins produced by streptococci and also puts forth a case for Streptococcus salivarius, a nonpathogenic and numerically predominant oral species, as an ideal candidate for development as the model probiotic for the oral cavity. S. salivarius is a safe species that not only produces broad-spectrum bacteriocins but harbors bacteriocin-encoding (and bacteriocin-inducing) transmissible DNA entities (megaplasmids).

Application of natural antimicrobials for food preservation

In this review, antimicrobials from a range of plant, animal, and microbial sources are reviewed along with their potential applications in food systems. Chemical and biochemical antimicrobial compounds derived from these natural sources and their activity against a range of pathogenic and spoilage microorganisms pertinent to food, together with their effects on food organoleptic properties, are outlined. Factors influencing the antimicrobial activity of such agents are discussed including extraction methods, molecular weight, and agent origin. These issues are considered in conjunction with the latest developments in the quantification of the minimum inhibitory (and noninhibitory) concentration of antimicrobials and/or their components. Natural antimicrobials can be used alone or in combination with other novel preservation technologies to facilitate the replacement of traditional approaches. Research priorities and future trends focusing on the impact of product formulation, intrinsic product parameters, and extrinsic storage parameters on the design of efficient food preservation systems are also presented.

In vitro and in vivo safety evaluation of the bacteriocin producer Streptococcus macedonicus ACA-DC 198

Streptococcus macedonicus ACA-DC 198, a bacteriocin producer isolated from Greek Kasseri cheese, was used in a series of in vitro and in vivo experiments in order to evaluate its pathogenic potential. The strain was examined in vitro for haemolytic activity, antibiotic resistance and presence of pathogenicity genes encountered in Streptococcus pyogenes. Subsequently, the strain was orally administered to mice (8.9 log cfu daily), continuously over a period of 12 weeks, in order to ascertain the effects of its long term consumption on animal health and gastric inflammation. S. macedonicus ACA-DC 198 was found to be non-haemolytic and sensitive to ampicillin, chloramphenicol, ciprofloxacin, erythromycin, streptomycin, tetracycline, and vancomycin, with the only resistance observed against kanamycin. PCR amplification and DNA-DNA hybridization did not reveal the presence of any of the S.pyogenes pathogenicity genes examined, namely emm, scpA, hasA, speB, smez2, speJ, sagAB, hylA, ska, speF, speG, slo, hylP2 and mga. In the mouse study, no detrimental effects were observed in the behaviour, general well being, weight gain and water consumption of the animals receiving S. macedonicus ACA-DC 198. Histologic analysis showed no evidence of inflammation in the stomach of the animals receiving S. macedonicus ACA-DC 198, while faecal microbiological analysis revealed that the strain retained its viability passing through the mouse gastrointestinal tract. Finally, no evidence of translocation to the liver, spleen and mesenteric lymph nodes was observed. In conclusion, none of the examined virulence determinants were detected in S. macedonicus ACA-DC 198 and its long term, high dosage oral administration did not appear to induce any pathogenic effect in mice.

Microbial interactions in cheese: implications for cheese quality and safety

The cheese microbiota, whose community structure evolves through a succession of different microbial groups, plays a central role in cheese-making. The subtleties of cheese character, as well as cheese shelf-life and safety, are largely determined by the composition and evolution of this microbiota. Adjunct and surface-ripening cultures marketed today for smear cheeses are inadequate for adequately mimicking the real diversity encountered in cheese microbiota. The interactions between bacteria and fungi within these communities determine their structure and function. Yeasts play a key role in the establishment of ripening bacteria. The understanding of these interactions offers to enhance cheese flavour formation and to control and/or prevent the growth of pathogens and spoilage microorganisms in cheese.

Functional properties of novel protective lactic acid bacteria and application in raw chicken meat against Listeria monocytogenes and Salmonella enteritidis

In this study 635 lactic acid bacteria of food origin were evaluated for their potential application as protective cultures in foods. A stepwise selection method was used to obtain the most appropriate strains for application as protective cultures in chicken meat. Specifically, all strains were examined for antimicrobial activity against various Gram positive and Gram negative pathogenic and spoilage bacteria. Strains exhibiting anti-bacterial activity were subsequently examined for survival in simulated food processing and gastrointestinal tract conditions, such as high temperatures, low pH, starvation and the presence of NaCl and bile salts. Selected strains where then examined for basic safety properties such as antibiotic resistance and haemolytic potential, while their antimicrobial activity was further investigated by PCR screening for possession of known bacteriocin genes. Two chosen strains were then applied on raw chicken meat to evaluate their protective ability against two common food pathogens, Listeria monocytogenes and Salmonella enteritidis, but also to identify potential spoilage effects by the application of the protective cultures on the food matrix. Antimicrobial activity in vitro was evident against Gram positive indicators, mainly Listeria and Brochothrix spp., while no antibacterial activity was obtained against any of the Gram negative bacteria tested. The antimicrobial activity was of a proteinaceous nature while strains with anti-listerial activity were found to possess one or more bacteriocin genes, mainly enterocins. Strains generally exhibited sensitivity to pH 2.0, but good survival at 45 degrees C, in the presence of bile salts and NaCl as well as during starvation, while variable survival rates were obtained at 55 degrees C. None of the strains was found to be haemolytic while variable antibiotic resistance profiles were obtained. Finally, when the selected strains Enterococcus faecium PCD71 and Lactobacillus fermentum ACA-DC179 were applied as protective cultures in chicken meat against L. monocytogenes and S. enteritidis respectively, a significantly reduced growth of these pathogenic bacteria was observed. In addition, these two strains did not appear to have any detrimental effect on biochemical parameters related to spoilage of the chicken meat.

A unique lantibiotic, thermophilin 1277, containing a disulfide bridge and two thioether bridges

AIMS

To identify the chemical structure of a bacteriocin, thermophilin 1277, produced by Streptococcus thermophilus SBT1277.

METHODS AND RESULTS

Thermophilin 1277 was purified and partial N-terminal sequence analysis revealed 6 unidentified amino acids amongst 31 amino acids residues. A 2.7-kbp region containing the thermophilin 1277 structural gene (tepA) encoding 58 amino acids was cloned and sequenced. Mature thermophilin 1277 (33 amino acids) was preceded by a 25-amino acid putative leader peptide containing a double glycine cleavage motif. Peptide sequence analysis following chemical modification of thermophilin 1277 revealed that the Cys21 and Cys29 residues form a disulfide bridge and that Thr8 or Thr10 forms two 3-methyllanthionines with Cys13 or Cys32 via thioether bridges. Antimicrobial activity was disrupted by ethanethiol or reductive agent treatments, indicating that the internal amino acid modifications are crucial for the activity.

CONCLUSIONS

Thermophilin 1277 from Strep. thermophilus SBT1277 belongs to the class of AII-type lantibiotics that has a disulfide and two thioether bridges.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first report of a lantibiotic produced by a GRAS species of Strep. thermophilus; thermophilin 1277 has a unique structure containing both a disulfide bridge and two thioether bridges that are crucial for its activity.