Evidence for horizontal gene transfer as origin of putrescine production in Oenococcus oeni RM83

The Role of Enterococcus faecium as a Key Producer and Fermentation Condition as an Influencing Factor in Tyramine Accumulation in Cheonggukjang

The study evaluated the role of Enterococcus faecium in tyramine production and its response to fermentation temperature in a traditional Korean fermented soybean paste, Cheonggukjang. Tyramine content was detected in retail Cheonggukjang products at high concentrations exceeding the recommended limit up to a factor of 14. All retail Cheonggukjang products contained Enterococcus spp. at concentrations of at least 6 Log CFU/g. Upon isolation of Enterococcus strains, approximately 93% (157 strains) produced tyramine at over 100 µg/mL. The strains that produced the highest concentrations of tyramine (301.14–315.29 μg/mL) were identified as E. faecium through 16S rRNA sequencing. The results indicate that E. faecium is one of the major contributing factors to high tyramine content in Cheonggukjang. During fermentation, tyramine content in Cheonggukjang groups co-inoculated with E. faecium strains was highest at 45 °C, followed by 37 °C and 25 °C. The tyramine content of most Cheonggukjang groups continually increased as fermentation progressed, except groups fermented at 25 °C. At 45 °C, the tyramine content occasionally exceeded the recommended limit within 3 days of fermentation. The results suggest that lowering fermentation temperature and shortening duration may reduce the tyramine content of Cheonggukjang, thereby reducing the safety risks that may arise when consuming food with high tyramine concentrations.

Effect of Fermentation, Drying and Roasting on Biogenic Amines and Other Biocompounds in Colombian Criollo Cocoa Beans and Shells

The composition of microbiota and the content and pattern of bioactive compounds (biogenic amines, polyphenols, anthocyanins and flavanols), as well as pH, color, antioxidant and reducing properties were investigated in fermented Criollo cocoa beans and shells. The analyses were conducted after fermentation and drying (T1) and after two thermal roasting processes (T2, 120 °C for 22 min; T3, 135 °C for 15 min). The fermentation and drying practices affected the microbiota of beans and shells, explaining the great variability of biogenic amines (BAs) content. Enterobacteriaceae were counted in a few samples with average values of 10³ colony forming units per gram (CFU g⁻¹), mainly in the shell, while Lactobacillus spp. was observed in almost all the samples, with the highest count in the shell with average values of 10⁴ CFU g⁻¹. After T1, the total BAs content was found to be in a range of 4.9÷127.1 mg kg⁻¹_DFW; what was remarkable was the presence of cadaverine and histamine, which have not been reported previously in fermented cocoa beans. The total BAs content increased 60% after thermal treatment T2, and of 21% after processing at T3, with a strong correlation (p < 0.05) for histamine (ß = 0.75) and weakly correlated for spermidine (ß = 0.58), spermine (ß = 0.50), cadaverine (ß = 0.47) and serotonine (ß = 0.40). The roasting treatment of T3 caused serotonin degradation (average decrease of 93%) with respect to unroasted samples. However, BAs were detected in a non-alarming concentration (e.g., histamine: n.d ÷ 59.8 mg kg⁻¹_DFW; tyramine: n.d. ÷ 26.5 mg kg⁻¹_DFW). Change in BAs level was evaluated by principal component analysis. PC1 and PC2 explained 84.9% and 4.5% of data variance, respectively. Antioxidant and reducing properties, polyphenol content and BAs negatively influenced PC1 with both polyphenols and BA increasing during roasting, whereas PC1 was positively influenced by anthocyanins, catechin and epicatechin.

Occurrence and Reduction of Biogenic Amines in Kimchi and Korean Fermented Seafood Products

Biogenic amines produced during fermentation may be harmful when ingested in high concentrations. As current regulations remain insufficient to ensure the safety of fermented vegetable products, the current study determined the risks associated with the consumption of kimchi by evaluating the biogenic amine concentrations reported by various studies. Upon evaluation, some kimchi products were found to contain histamine and tyramine at potentially hazardous concentrations exceeding the recommended limit of 100 mg/kg for both histamine and tyramine. The biogenic amines may have originated primarily from metabolic activity by microorganisms during fermentation, as well as from Jeotgal (Korean fermented seafood) and Aekjeot (Korean fermented fish sauce) products commonly used as ingredients for kimchi production. Many studies have suggested that Jeotgal and Aekjeot may contribute to the histamine and tyramine content in kimchi. Microorganisms isolated from kimchi and Jeotgal have been reported to produce both histamine and tyramine. Despite the potential toxicological risks, limited research has been conducted on reducing the biogenic amine content of kimchi and Jeotgal products. The regulation and active monitoring of biogenic amine content during kimchi production appear to be necessary to ensure the safety of the fermented vegetable products.

Biogenic Amine Production by Lactic Acid Bacteria: A Review

Lactic acid bacteria (LAB) are considered as the main biogenic amine (BA) producers in fermented foods. These compounds derive from amino acid decarboxylation through microbial activities and can cause toxic effects on humans, with symptoms (headache, heart palpitations, vomiting, diarrhea) depending also on individual sensitivity. Many studies have focused on the aminobiogenic potential of LAB associated with fermented foods, taking into consideration the conditions affecting BA accumulation and enzymes/genes involved in the biosynthetic mechanisms. This review describes in detail the different LAB (used as starter cultures to improve technological and sensorial properties, as well as those naturally occurring during ripening or in spontaneous fermentations) able to produce BAs in model or in real systems. The groups considered were enterococci, lactobacilli, streptococci, lactococci, pediococci, oenococci and, as minor producers, LAB belonging to Leuconostoc and Weissella genus. A deeper knowledge of this issue is important because decarboxylase activities are often related to strains rather than to species or genera. Moreover, this information can help to improve the selection of strains for further applications as starter or bioprotective cultures, in order to obtain high quality foods with reduced BA content.

Lactobacillus rossiae strain isolated from sourdough produces putrescine from arginine

This work reports a Lactobacillus rossiae strain (L. rossiae D87) isolated from sourdough that synthesizes putrescine - a biogenic amine that raises food safety and spoilage concerns - from arginine via the ornithine decarboxylase (ODC) pathway. The odc and potE genes were identified and sequenced. These genes respectively encode ornithine decarboxylase (Odc), which participates in the decarboxylation of ornithine to putrescine, and the ornithine/putrescine exchanger (PotE), which exchanges ornithine for putrescine. Transcriptional analysis showed that odc and potE form an operon that is regulated transcriptionally by ornithine in a dose-dependent manner. To explore the possible role of the ODC pathway as an acid stress resistance mechanism for this bacterium, the effect of acidic pHs on its transcriptional regulation and on putrescine biosynthesis was analysed. Acidic pHs induced the transcription of the odc-potE genes and the production of putrescine over that seen at neutral pH. Further, putrescine production via the ODC system improved the survival of L. rossiae D87 by counteracting the acidification of the cytoplasm when the cells were subjected to acidic conditions. These results suggest the ODC pathway of L. rossiae D87 provides a biochemical defence mechanism against acidic environments.

Technological Properties and Biogenic Amines Production by Bacteriocinogenic Lactococci and Enterococci Strains Isolated from Raw Goat's Milk

Technological properties and biogenic amine production were analyzed in 56 bacteriocinogenic lactococci and enterococci strains isolated from raw goat's milk. Fifteen lactococci strains were able to reduce milk pH to 5.3 or lower after 6 h, while enterococci strains were initially slow in producing acids. Lactococcus lactis subsp. lactis GLc06 and three strains of Enterococcus faecalis (GEn20, GEn22, and GEn23) presented high proteolytic activity. L. lactis subsp. lactis GLc06 and E. faecalis GEn22 also showed a high percentage of autolysis after only 4 h, reaching 71.11 and 97.67%, respectively, after 24 h. No strain was able to secrete exopolysaccharides, and L. lactis subsp. lactis GLc22 and 25 of the Enterococcus strains were able to produce diacetyl. L. lactis subsp. lactis GLc05 and 23 of the Enterococcus strains presented a high tolerance to NaCl at 10% (wt/vol). Regarding biogenic amine production, 12 strains (5 lactococci and 7 enterococci) were capable of forming tyramine and 4 strains (1 lactococcus and 3 enterococci) were capable of forming 2-phenylethylamine, but in very low amounts. GLc06 presented great acidifying, proteolytic, and autolytic activities, and GLc05 was capable of growing at high NaCl concentrations (10%, wt/vol), possessing medium autolytic and proteolytic activities. Some enterococci strains produced diacetyl and high autolytic and extracellular proteolytic activities and also presented resistance to high NaCl concentrations. The interesting technological properties presented by some bacteriocinogenic strains can justify their use by the dairy industry, with the aim of ensuring both safety due to bacteriocin production and technological transformations in fermented products.

Biogenic Amines in Dairy Products: Origin, Incidence, and Control Means

Biogenic amines (BAs) are toxic compounds produced by a number of microorganisms (bacteria, yeasts, and molds) as a result of the metabolism of some amino acid, usually decarboxylation reactions. BA-producing microorganisms are not necessarily pathogenic, such as lactic acid bacteria, which are, on the contrary, among the most beneficial microbiota to human beings and some of which even have probiotic properties. However, the incidence of BAs in dairy products and their possible implication in serious dairy-borne intoxications has long been overlooked. Consequently, the implementation of control measures to limit such an incidence has not been considered among the priorities of the food safety authorities. Nonetheless, there is a growing concern with regard to the presence of BAs in dairy products, because their toxicological status as toxins that may have serious acute and/or chronic adverse health effects is becoming increasingly evident and well-documented. The main BAs associated with dairy products are reviewed herein from the perspective of their incidence in these food products, and to draw the attention of readers to the shortage in data to perform pertinent risk assessment, which is considered to be a key action to provide efficient control means and to help decision makers issue appropriate legislative and regulatory measures.

Isolation and typification of histamine-producing Lactobacillus vaginalis strains from cheese

In food, the biogenic amine (BA) histamine is mainly produced by histidine decarboxylation catalysed by microbial histidine decarboxylase. The consumption of foods containing high concentrations of histamine can trigger adverse neurological, gastrointestinal and respiratory reactions. Indeed, histamine is one of the most toxic of all BAs, and is often detected in high concentration in cheese. However, little is known about the microorganisms responsible for its accumulation in this food. In the present work, 25 histamine-producing Lactobacillus vaginalis strains were isolated from a blue-veined cheese (the first time that histamine-producing strains of this species have been isolated from any food). The restriction profiles of their genomes were analysed by PFGE, and seven lineages identified. The presence of the histidine decarboxylase gene (hdcA) was confirmed by PCR. The nucleotide sequence and genetic organisation of the histamine biosynthesis gene cluster (HDC) and its flanking regions are described for a representative strain (L. vaginalis IPLA11050).

Implications of new research and technologies for malolactic fermentation in wine

The initial conversion of grape must to wine is an alcoholic fermentation (AF) largely carried out by one or more strains of yeast, typically Saccharomyces cerevisiae. After the AF, a secondary or malolactic fermentation (MLF) which is carried out by lactic acid bacteria (LAB) is often undertaken. The MLF involves the bioconversion of malic acid to lactic acid and carbon dioxide. The ability to metabolise L-malic acid is strain specific, and both individual Oenococcus oeni strains and other LAB strains vary in their ability to efficiently carry out MLF. Aside from impacts on acidity, LAB can also metabolise other precursors present in wine during fermentation and, therefore, alter the chemical composition of the wine resulting in an increased complexity of wine aroma and flavour. Recent research has focused on three main areas: enzymatic changes during MLF, safety of the final product and mechanisms of stress resistance. This review summarises the latest research and technological advances in the rapidly evolving study of MLF and investigates the directions that future research may take.

O risco das aminas biogênicas nos alimentos

Aminas biogênicas são bases orgânicas de baixo peso molecular com atividade biológica, produzidas a partir da ação da enzima descarboxilase. Microrganismos utilizados na fermentação de alimentos são capazes de produzi-las. O consumo desses compostos causam graves efeitos toxicológicos, indesejáveis para a saúde humana. Embora não exista legislação específica sobre a quantidade máxima permitida de aminas em alimentos e bebidas, a presença e o acumulo destes compostos é de grande importância. O objetivo desta revisão é evidenciar a necessidade de mais estudos e discutir a presença de aminas biogênicas em alimentos variados.

Production of tyramine by Enterococcus faecalis strains in water-boiled salted duck

The potential to produce biogenic amines was investigated with 15 Lactococcus lactis and 15 Enterococcus faecalis strains isolated from water-boiled salted duck. The production of biogenic amines from the isolated strains grown in de Man Rogosa Sharpe broth containing precursor amino acids was determined by thin-layer chromatography and high-performance liquid chromatography. None of the L. lactis strains produced any biogenic amines, whereas 12 strains of E. faecalis produced tyramine and b -phenylethylamine. PCR assays were used to detect the presence of tyrosine decarboxylase genes in all of the isolated strains. Only the 12 biogenic amine-producing Enterococcus strains had a 924-bp fragment characteristic for the tyrosine decarboxylase gene. The comparison of the amplified partial tyrDC gene sequences of the 12 positive Enterococcus strains revealed 99% similarity within the same species. The tyramine production of the sterilized water-boiled salted duck inoculated with E. faecalis R612Z1 increased significantly during storage. This study reveals that the isolated E. faecalis strains can produce tyramine and β-phenylethylamine in the medium; however, they can only produce tyramine in water-boiled salted duck.

Three-component lysine/ornithine decarboxylation system in Lactobacillus saerimneri 30a

Lactic acid bacteria play a pivotal role in many food fermentations and sometimes represent a health threat due to the ability of some strains to produce biogenic amines that accumulate in foods and cause trouble following ingestion. These strains carry specific enzymatic systems catalyzing the uptake of amino acid precursors (e.g., ornithine and lysine), the decarboxylation inside the cell, and the release of the resulting biogenic amines (e.g., putrescine and cadaverine). This study aimed to identify the system involved in production of cadaverine from lysine, which has not been described to date for lactic acid bacteria. Strain Lactobacillus saerimneri 30a (formerly called Lactobacillus sp. 30a) produces both putrescine and cadaverine. The sequencing of its genome showed that the previously described ornithine decarboxylase gene was not associated with the gene encoding an ornithine/putrescine exchanger as in other bacteria. A new hypothetical decarboxylation system was detected in the proximity of the ornithine decarboxylase gene. It consisted of two genes encoding a putative decarboxylase sharing sequence similarities with ornithine decarboxylases and a putative amino acid transporter resembling the ornithine/putrescine exchangers. The two decarboxylases were produced in Escherichia coli, purified, and characterized in vitro, whereas the transporter was heterologously expressed in Lactococcus lactis and functionally characterized in vivo. The overall data led to the conclusion that the two decarboxylases and the transporter form a three-component decarboxylation system, with the new decarboxylase being a specific lysine decarboxylase and the transporter catalyzing both lysine/cadaverine and ornithine/putrescine exchange. To our knowledge, this is an unprecedented observation of a bacterial three-component decarboxylation system.

IS30 elements are mediators of genetic diversity in Oenococcus oeni

Oenococcus oeni is responsible for the malolactic fermentation of wines. Genomic diversity has been recently established in the species and extensive attention is now being given to the genomic bases of strain-specific differences. We explored the role of insertion sequences (IS), which are considered as driving forces for novel genotypic and phenotypic variants in prokaryotes. The present study focuses on members of the IS30 family, which are widespread among lactic acid bacteria. An in silico analysis of the three available genomes of O. oeni in combination with the use of an inverse PCR strategy targeting conserved IS30-related sequences indicated the presence of seven IS30 copies in the pangenome of O. oeni. A primer designed to anneal to the conserved 3' end of the IS30 element was paired with each of the seven primers selected to bind to unique sequences upstream of each of the seven mobile elements identified. The study presents an overview of the abundance, and the genomic environment of IS30 elements in the O. oeni pangenome and shows that the two existing genetic sub-populations previously described in the species through multilocus sequence typing analysis (MLST) differ in their IS30 content. Possible IS30 impacts on bacterial adaptation are discussed.

Tyramine and phenylethylamine biosynthesis by food bacteria

Tyramine poisoning is caused by the ingestion of food containing high levels of tyramine, a biogenic amine. Any foods containing free tyrosine are subject to tyramine formation if poor sanitation and low quality foods are used or if the food is subject to temperature abuse or extended storage time. Tyramine is generated by decarboxylation of the tyrosine through tyrosine decarboxylase (TDC) enzymes derived from the bacteria present in the food. Bacterial TDC have been only unequivocally identified and characterized in Gram-positive bacteria, especially in lactic acid bacteria. Pyridoxal phosphate (PLP)-dependent TDC encoding genes (tyrDC) appeared flanked by a similar genetic organization in several species of lactic acid bacteria, suggesting a common origin by a single mobile genetic element. Bacterial TDC are also able to decarboxylate phenylalanine to produce phenylethylamine (PEA), another biogenic amine. The molecular knowledge of the genes involved in tyramine production has led to the development of molecular methods for the detection of bacteria able to produce tyramine and PEA. These rapid and simple methods could be used for the analysis of the ability to form tyramine by bacteria in order to evaluate the potential risk of tyramine biosynthesis in food products.

Factors influencing biogenic amines accumulation in dairy products

Fermented foods are among the food products more often complained of having caused episodes of biogenic amines (BA) poisoning. Concerning milk-based fermented foods, cheese is the main product likely to contain potentially harmful levels of BA, specially tyramine, histamine, and putrescine. Prompted by the increasing awareness of the risks related to dietary uptake of high biogenic amine loads, in this review we report all those elaboration and processing technological aspects affecting BA biosynthesis and accumulation in dairy foods. Improved knowledge of the factors involved in the synthesis and accumulation of BA should lead to a reduction in their incidence in milk products. Synthesis of BA is possible only when three conditions converge: (i) availability of the substrate amino acids; (ii) presence of microorganisms with the appropriate catabolic pathway activated; and (iii) environmental conditions favorable to the decarboxylation activity. These conditions depend on several factors such as milk treatment (pasteurization), use of starter cultures, NaCl concentration, time, and temperature of ripening and preservation, pH, temperature, or post-ripening technological processes, which will be discussed in this chapter.

Evidence of two functionally distinct ornithine decarboxylation systems in lactic acid bacteria

Biogenic amines are low-molecular-weight organic bases whose presence in food can result in health problems. The biosynthesis of biogenic amines in fermented foods mostly proceeds through amino acid decarboxylation carried out by lactic acid bacteria (LAB), but not all systems leading to biogenic amine production by LAB have been thoroughly characterized. Here, putative ornithine decarboxylation pathways consisting of a putative ornithine decarboxylase and an amino acid transporter were identified in LAB by strain collection screening and database searches. The decarboxylases were produced in heterologous hosts and purified and characterized in vitro, whereas transporters were heterologously expressed in Lactococcus lactis and functionally characterized in vivo. Amino acid decarboxylation by whole cells of the original hosts was determined as well. We concluded that two distinct types of ornithine decarboxylation systems exist in LAB. One is composed of an ornithine decarboxylase coupled to an ornithine/putrescine transmembrane exchanger. Their combined activities results in the extracellular release of putrescine. This typical amino acid decarboxylation system is present in only a few LAB strains and may contribute to metabolic energy production and/or pH homeostasis. The second system is widespread among LAB. It is composed of a decarboxylase active on ornithine and l-2,4-diaminobutyric acid (DABA) and a transporter that mediates unidirectional transport of ornithine into the cytoplasm. Diamines that result from this second system are retained within the cytosol.

Wine features related to safety and consumer health: an integrated perspective

This review presents a global view of the current situation of the scientific knowledge about aspects of wine with possible repercussions (positive or negative) on consumer health and wine safety. The presence in wine of some potential harmful compounds such as phytosanitary products, trace metal compounds, sulfites, and some toxics of microbial origin, such as ochratoxin A, ethyl carbamate, and biogenic amines, is discussed. The different strategies and alternative methodologies that are being carried out to reduce or to avoid the presence of these substances in wines are also discussed. In recent years much work has focused on establishing the scientific explanations for the positive biological effects of some wine compounds. In this review, we also examine the latest knowledge regarding wine and health, focusing on two types of compounds that have been related to the positive effects of moderate wine consumption, such as phenolic compounds and bioactive peptides.

Is the production of the biogenic amines tyramine and putrescine a species-level trait in enterococci?

Biogenic amines (BA) are toxic nitrogenous compounds that can be accumulated in foods via the microbial decarboxylation of certain amino acids. Lactic acid bacteria (LAB) strains belonging to different species and genera have been described as BA producers and are mainly responsible for their synthesis in fermented foods. It is generally accepted that the capacity to produced BAs is strain-dependent. However, the large number of enterococci identified as BA producers suggests that the aminogenic trait may be a species-level characteristic. Enterococcus faecalis, Enterococcus faecium and Enterococcus durans strains of different origin were analysed to determine their capacity to produce tyramine and putrescine. The presence of the genes responsible for this and the identity of their flanking regions were checked by PCR. The results suggest that tyramine biosynthesis is a species-level characteristic in E. faecalis, E. faecium and E. durans. Putrescine synthesis was found to be a species-level trait of E. faecalis, with production occurring via the agmatine deamination pathway. Some E. faecium strains of human origin also produced putrescine; this trait was probably acquired via horizontal gene transfer.

Molecular cloning, heterologous expression, and characterization of Ornithine decarboxylase from Oenococcus oeni

Ornithine decarboxylase (ODC) is responsible for the production of putrescine, the major biogenic amine found in wine. Oenococcus oeni is the most important lactic acid bacterium in the winemaking process and is involved in malolactic fermentation. We report here the characterization of ODC from an O. oeni strain isolated from wine. Screening of 263 strains isolated from wine and cider from all over the world revealed that the presence of the odc gene appears to be strain specific in O. oeni. After cloning, heterologous expression in Escherichia coli, and characterization, the enzyme was found to have a molecular mass of 85 kDa and a pI of 6.2 and revealed maximal activity at pH 5.5 and an optimum temperature of 35°C. Kinetic studies showed that O. oeni ODC is specific for L-ornithine with a K(m) value of 1 mM and a V(max) of 0.57 U·mg(-1). The hypothesis that cadaverine, which results from lysine decarboxylation, may be linked to putrescine production is not valid since O. oeni ODC cannot decarboxylate L-lysine. As no lysine decarboxylase was detected in any of the O. oeni genomes sequenced, cadaverine synthesis may result from another metabolic pathway. This work is the first characterization of an ODC from a lactic acid bacterium isolated from a fermented product.

Sequencing and transcriptional analysis of the biosynthesis gene cluster of putrescine-producing Lactococcus lactis

Lactococcus lactis is a prokaryotic microorganism with great importance as a culture starter and has become the model species among the lactic acid bacteria. The long and safe history of use of L. lactis in dairy fermentations has resulted in the classification of this species as GRAS (General Regarded As Safe) or QPS (Qualified Presumption of Safety). However, our group has identified several strains of L. lactis subsp. lactis and L. lactis subsp. cremoris that are able to produce putrescine from agmatine via the agmatine deiminase (AGDI) pathway. Putrescine is a biogenic amine that confers undesirable flavor characteristics and may even have toxic effects. The AGDI cluster of L. lactis is composed of a putative regulatory gene, aguR, followed by the genes (aguB, aguD, aguA, and aguC) encoding the catabolic enzymes. These genes are transcribed as an operon that is induced in the presence of agmatine. In some strains, an insertion (IS) element interrupts the transcription of the cluster, which results in a non-putrescine-producing phenotype. Based on this knowledge, a PCR-based test was developed in order to differentiate nonproducing L. lactis strains from those with a functional AGDI cluster. The analysis of the AGDI cluster and their flanking regions revealed that the capacity to produce putrescine via the AGDI pathway could be a specific characteristic that was lost during the adaptation to the milk environment by a process of reductive genome evolution.

Suppression subtractive hybridization identifies bacterial genomic regions that are possibly involved in hBD-2 regulation by enterocytes

SCOPE

Human β-defensin 2 (hBD-2) is an inducible antimicrobial peptide synthesized by the epithelium to counteract bacterial adherence and invasion. It has been suggested that probiotic bacteria sustain gut barrier function via induction of defensins. The goals of this study were (i) to evaluate the potential immunomodulatory effects of 11 different Lactobacillus fermentum strains isolated from Kimere, an African fermented pearl millet (Pennisetum glaucum) dough, on the hBD-2 secretion by human intestinal CaCo-2 cell line and (ii) to examine genetic differences between two strains of L. fermentum (K2-Lb4 and K11-Lb3) which differed in their effect on the production of hBD-2 in this study.

METHODS AND RESULTS

Totally, 46 strains of L. fermentum from Kimere were isolated and characterized using molecular biology methods including pulsed-field gel electrophoresis patterns. After performing time- and dose-experiments, CaCo-2 cells were incubated with or without bacteria for 12 h. L. fermentum PZ1162 was included as the positive control. Cell-free supernatants were analyzed for hBD-2 protein by enzyme-linked immunosorbent assay (ELISA). To identify potential bacterial genes associated with hBD-2 regulation, suppression subtractive hybridization (SSH) was used. Among the 11 strains tested, only two strains of bacteria, K11-Lb3 and K2-Lb6, significantly induced the production of hBD-2 by CaCo-2 cells. This effect was strain-specific, dose-dependent and particularly seems to be bacterial genomic-dependent as manifested by SSH. L. fermentum strains with and without hBD-2 inducing effect differed in genes encoding proteins involved in glycosylation of cell-wall proteins e.g. glycosyltransferase, UDP-N-acetylglucosamine 2-epimerase, rod shape-determining protein MreC, lipoprotein precursors, sugar ABC transporters, and glutamine ABC transporter ATP-binding protein.

CONCLUSION

This study implies that certain strains of L. fermentum isolated from Kimere may stimulate the intestinal innate defense through the induction of hBD-2. The molecular basis of hBD-2 induction by L. fermentum strain K11-Lb3 may be based on glycosylated cell-surface structures synthesized with the aid of glycosyltransferase, UDP-N-acetylglucosamine 2-epimerase, and rod shape-determining protein MreC.

Characterization of the tyramine-producing pathway in Sporolactobacillus sp. P3J

A sporulated lactic acid bacterium (LAB) isolated from cider must was shown to harbour the tdc gene encoding tyrosine decarboxylase. The isolate belonged to the Sporolactobacillus genus and may correspond to a novel species. The ability of the tdc-positive strain, Sporolactobacillus sp. strain P3J, to produce tyramine in vitro was demonstrated by using HPLC. A 7535 bp nucleotide sequence harbouring the putative tdc gene was determined. Analysis of the obtained sequence showed that four tyramine production-associated genes [tyrosyl-tRNA synthetase (tyrS), tyrosine decarboxylase (tdc), tyrosine permease (tyrP) and Na(+)/H(+) antiporter (nhaC)] were present and were organized as already described in other tyramine-producing LAB. This operon was surrounded by genes showing the highest identities with mobile elements: a putative phage terminase and a putative transposase (downstream and upstream, respectively), suggesting that the tyramine-forming trait was acquired through horizontal gene transfer. Transcription analyses of the tdc gene cluster suggested that tyrS and nhaC are expressed as monocistronic genes while tdc would be part of a polycistronic mRNA together with tyrP. The presence of tyrosine in the culture medium induced the expression of all genes except for tyrS. A clear correlation was observed between initial tyrosine concentration and tyramine production combined with an increase in the final pH reached by the culture. Finally, cloning and expression of the tyrP gene in Lactococcus lactis demonstrated that its product catalyses the exchange of tyrosine and tyramine.

Occurrence of biogenic amine-forming lactic acid bacteria in wine and cider

A collection of 810 lactic acid bacteria (LAB) strains isolated from wine and cider was screened for potential biogenic amine (BA) producers by combining molecular and phenotypic approaches. A newly developed multiplex PCR method allowed for the simultaneous detection of four genes involved in the production of histamine (histidine decarboxylase, hdc), tyramine (tyrosine decarboxylase, tyrdc) and putrescine (via either ornithine decarboxylase, odc, or agmatine deiminase, agdi) while TLC and HPLC analysis allowed for BA-production determination. One hundred and fifty-eight LAB strains were monitored by the molecular/phenotypic double approach and revealed a good correlation between genotypic and phenotypic data. Eighteen per cent of the tested strains were positive for at least one BA target gene with up to three detected simultaneously, in particular amongst Lactobacillus brevis and Lactobacillus hilgardii isolates for the tyrdc and agdi genes. The most frequent gene corresponded to the agdi gene detected in 112 strains (14% of all LAB strains) of 10 different LAB species. The tyrdc gene was detected in 67 strains represented by 7 different LAB species (8% overall), especially those isolated from wine. Lower levels of hdc(+) (2% of strains) and especially odc(+) (0.5% of strains) strains were observed. Interestingly, species that have never been described to carry BA-producing pathway genes were identified in this study. Furthermore, only one cadaverine-producer was detected and corresponded to Lactobacillus 30a, a collection strain not found in fermented beverages, although cadaverine is commonly detected in wines.

Origin of the putrescine-producing ability of the coagulase-negative bacterium Staphylococcus epidermidis 2015B

A multiplex PCR method, aimed at the detection of genes associated with biogenic amine production, identified the odc gene encoding ornithine decarboxylase in 1 of 15 strains of Staphylococcus epidermidis. The ability of the positive strain, S. epidermidis 2015B, to produce putrescine in vitro was demonstrated by high-performance liquid chromatography (HPLC). In this strain, the odc gene was detected on plasmid DNA, suggesting that the ability to form putrescine is carried by a mobile element, which explains the fact that the trait is strain dependent within the S. epidermidis species. A 6,292-bp nucleotide sequence harboring the putative odc gene was determined. S. epidermidis ornithine decarboxylase (ODC) showed 60 to 65% sequence identity with known ODCs of Gram-positive as well as Gram-negative bacteria. Downstream of the odc gene, a gene encoding a putative amino acid transporter was found that shared 59% sequence identity with the ornithine/putrescine exchanger (PotE) of Escherichia coli. Cloning and expression of the potE gene of S. epidermis 2015B in Lactococcus lactis demonstrated that the gene product transported ornithine and putrescine into the cells and efficiently exchanged putrescine for ornithine. Analysis of the flanking regions showed high identity levels with different S. epidermidis plasmid sequences, which would confirm the plasmidic location of the odc operon. It follows that the odc and potE gene pair encodes a putrescine-producing pathway in S. epidermis 2015B that was acquired through horizontal gene transfer.

Fluidized muds: a novel setting for the generation of biosphere diversity through geologic time

Reworked and fluidized fine-grained deposits in energetic settings are a major modern-day feature of river deltas and estuaries. Similar environments were probably settings for microbial evolution on the early Earth. These sedimentary systems act as efficient biogeochemical reactors with high bacterial phylogenetic diversity and functional redundancy. They are temporally rather than spatially structured, with repeated cycling of redox conditions and successive stages of microbial metabolic processes. Intense reworking of the fluidized bed entrains bacteria from varied habitats providing new, diverse genetic materials to contribute to horizontal gene transfer events and the creation of new bacterial ecotypes. These vast mud environments may act as exporters and promoters of biosphere diversity and novel adaptations, potentially on a globally important scale.

Characterization of an acquired dps-containing gene island in the lactic acid bacterium Oenococcus oeni

AIMS

To identify novel actors responsible for the marked adaptation of the Oenococcus oeni species to its environment.

METHODS AND RESULTS

Genomic surveillance of the available genome sequences from O. oeni indicated the presence of a small ORF, encoding a protein named Dps(A). The cloned gene complemented the dps(-) mutant of Escherichia coli and conferred resistance to hydrogen peroxide, wine, and metals. The dps(A) gene was flanked by IS-related elements. The entire region was characterized by an anomalously high GC content compared to those reported for oenococcal genomes. The dps(A) gene was present in 15 of the 38 tested isolates. Positive strains originated from different geographical areas and sources. No change in tolerance to wine or to oxidative stress was observed between O. oeni strains harbouring dps(A) and those not harbouring this gene.

CONCLUSIONS

Some O. oeni have acquired a functional homologue to the dps gene from E. coli as part of a mobile element.

SIGNIFICANCE AND IMPACT OF THE STUDY

Dps(A) probably increases the bacterial fitness in response to environmental challenges. However, the physiological condition under which it adds a selective advantage to O. oeni during winemaking remains to be found.

Oenococcus oeni genome plasticity is associated with fitness

Oenococcus oeni strains are well-known for their considerable phenotypic variations in terms of tolerance to harsh wine conditions and malolactic activity. Genomic subtractive hybridization (SH) between two isolates with differing enological potentials was used to elucidate the genetic bases of this intraspecies diversity and identify novel genes involved in adaptation to wine. SH revealed 182 tester-specific fragments corresponding to 126 open reading frames (ORFs). A large proportion of the chromosome-related ORFs resembled genes involved in carbohydrate transport and metabolism, cell wall/membrane/envelope biogenesis, and replication, recombination, and repair. Six regions of genomic plasticity were identified, and their analysis suggested that both limited recombination and insertion/deletion events contributed to the vast genomic diversity observed in O. oeni. The association of selected sequences with adaptation to wine was further assessed by screening a large collection of strains using PCR. No sequences were found to be specific to highly performing (HP) strains alone. However, there was a statistically significant positive association between HP strains and the presence of eight gene sequences located on regions 2, 4, and 5. Gene expression patterns were significantly modified in HP strains, following exposure to one or more of the common stresses in wines. Regions 2 and 5 showed no traces of mobile elements and had normal GC content. In contrast, region 4 had the typical hallmarks of horizontal transfer, suggesting that the strategy of acquiring genes from other bacteria enhances the fitness of O. oeni strains.

Characterization of gtf, a glucosyltransferase gene in the genomes of Pediococcus parvulus and Oenococcus oeni, two bacterial species commonly found in wine

"Ropiness" is a bacterial alteration in wines, beers, and ciders, caused by beta-glucan-synthesizing pediococci. A single glucosyltransferase, Gtf, controls ropy polysaccharide synthesis. In this study, we show that the corresponding gtf gene is also present on the chromosomes of several strains of Oenococcus oeni isolated from nonropy wines. gtf is surrounded by mobile elements that may be implicated in its integration into the chromosome of O. oeni. gtf is expressed in all the gtf(+) strains, and beta-glucan is detected in the majority of these strains. Part of this beta-glucan accumulates around the cells forming a capsule, while the other part is liberated into the medium together with heteropolysaccharides. Most of the time, this polymer excretion does not lead to ropiness in a model medium. In addition, we show that wild or recombinant bacterial strains harboring a functional gtf gene (gtf(+)) are more resistant to several stresses occurring in wine (alcohol, pH, and SO(2)) and exhibit increased adhesion capacities compared to their gtf mutant variants.

Agmatine deiminase pathway genes in Lactobacillus brevis are linked to the tyrosine decarboxylation operon in a putative acid resistance locus

In lactic acid bacteria (LAB), amino acids and their derivatives may be converted into amine-containing compounds designated biogenic amines, in pathways providing metabolic energy and/or acid resistance to the bacteria. In a previous study, a pathway converting tyrosine to tyramine was detected in Lactobacillus brevis and a fragment of a gene possibly involved in the production of another biogenic amine, putrescine, from agmatine, was detected in the same locus. The present study was carried out to determine if Lb. brevis actually harbours two biogenic amine-producing pathways in the same locus and to investigate the occurrence of the two gene clusters in other bacteria. Sequencing of the DNA locus in Lb. brevis revealed a cluster of six genes that are related to previously reported genes of agmatine deiminase pathways but with marked differences such as two genes encoding putative agmatine deiminases rather than one. Heterologous expression of encoded enzymes confirmed the presence of at least one active agmatine deiminase and one amino acid transporter that efficiently exchanged agmatine and putrescine. It was concluded that the Lb. brevis gene cluster encodes a functional and highly specific agmatine deiminase pathway. Screening of a collection of 197 LAB disclosed the same genes in 36 strains from six different species, and almost all the positive bacteria also contained the tyrosine catabolic pathway genes in the same locus. These results support the hypothesis that the agmatine deiminase and tyrosine catabolic pathways belong to a genomic region that provides acid resistance and that is exchanged horizontally as a whole between LAB.