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

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.

Tyramine and tyrosine decarboxylase gene contributes to the formation of cyanic blotches in the petals of pansy (Viola × wittrockiana)

Tyrosine decarboxylase (TYDC) can catalyze tyrosine into tyramine. Several studies demonstrated its roles in the acidity, salidroside and defense response. Here we found that TYDC from Viola × wittrockiana Gam (VwTYDC) may contribute to the formation of cyaninc blotches in the petal. VwTYDC gene were cloned from Viola × wittrockiana and the cDNA full-length sequences were 1634 bp encoding 494 amino acids. Gene expression of VwTYDC in different tissues and developmental stages showed that they were significantly higher expressed in flowers than stems, leaves and roots. In addition, VwTYDC expression were higher in cyanic blotches than those observed in acyanic blotches of petal. Metabolites analysis showed the contents of tyramine in cyanic blotches were also higher than that in acyanic areas. Furthermore, in vitro assay revealed the absorption peak of anthocyanins had a red shift and an increase when fed tyramine. We speculated that tyramine might contribute to flower color expression of pansy as co-pigment. Our study demonstrated for the first time that the contents of tyramine led to flower blotches formation in cyanic blotches of the petals in plant flowers, and this may due to the higher expression of VwTYDC gene.

Growth, biogenic amine production and tyrDC transcription of Enterococcus faecalis in synthetic medium containing defined amino acid concentrations

AIMS

The tyraminogenic potential of the strains Enterococcus faecalis EF37 and ATCC 29212 was investigated in a synthetic medium containing defined amounts of tyrosine and phenylalanine at different temperatures.

METHODS AND RESULTS

Enterococci growth and the production of biogenic amines (BA) were evaluated in relation to their pre-growth in medium containing tyrosine. Significant differences between the two strains were evidenced at metabolic level. Both the pre-adapted strains grew faster in all the tested conditions, independently of the presence of the precursor. Temperatures of 30 and 40°C positively affected the growth parameters. The tyrosine decarboxylase (tyrDC) activity of the strain EF37 was positively affected by pre-adaptation, while ATCC 29212 showed a faster and higher tyramine accumulation with not-adapted cells. The expression analysis of the gene tyrDC confirmed the influence of the growth conditions on gene transcription.

CONCLUSIONS

The small differences found between the two strains in the maximum transcript level reached rapidly after the inoculum and the different behaviour in the tyramine accumulation suggested the possible involvement of complex regulation mechanisms on the tyrDC or on the membrane transport systems, which could affect the different BA accumulation trend.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study gives deeper insight into the metabolic regulation of tyrDC activity of enterococci.

Crystal structure of tyrosine decarboxylase and identification of key residues involved in conformational swing and substrate binding

Tyrosine decarboxylase (TDC) is a pyridoxal 5-phosphate (PLP)-dependent enzyme and is mainly responsible for the synthesis of tyramine, an important biogenic amine. In this study, the crystal structures of the apo and holo forms of Lactobacillus brevis TDC (LbTDC) were determined. The LbTDC displays only 25% sequence identity with the only reported TDC structure. Site-directed mutagenesis of the conformationally flexible sites and catalytic center was performed to investigate the potential catalytic mechanism. It was found that H241 in the active site plays an important role in PLP binding because it has different conformations in the apo and holo structures of LbTDC. After binding to PLP, H241 rotated to the position adjacent to the PLP pyridine ring. Alanine scanning mutagenesis revealed several crucial regions that determine the substrate specificity and catalytic activity. Among the mutants, the S586A variant displayed increased catalytic efficiency and substrate affinity, which is attributed to decreased steric hindrance and increased hydrophobicity, as verified by the saturation mutagenesis at S586. Our results provide structural information about the residues important for the protein engineering of TDC to improve catalytic efficiency in the green manufacturing of tyramine.

Multiple omics uncovers host-gut microbial mutualism during prebiotic fructooligosaccharide supplementation

Fructooligosaccharide (FOS), a prebiotic well known for its health-promoting properties, can improve the human gut ecosystem most likely through changes in its microbial composition. However, the detailed mechanism(s) of action of FOS in the modulation of the gut ecosystem remain(s) obscure. Traditional methods of profiling microbes and metabolites could barely show any significant features due to the existence of large interindividual differences, but our novel microbe–metabolite correlation approach, combined with faecal immunoglobulin A (IgA) measurements, has revealed that the induction of mucosal IgA by FOS supplementation correlated with the presence of specific bacteria. Furthermore, the metabolic dynamics of butyrate, l-phenylalanine, l-lysine and tyramine were positively correlated with that of these bacteria and IgA production, whereas p-cresol was negatively correlated. Taken together, our focused intraindividual analysis with omics approaches is a powerful strategy for uncovering the gut molecular network and could provide a new vista for understanding the human gut ecosystem.

Tyrosine-containing peptides are precursors of tyramine produced by Lactobacillus plantarum strain IR BL0076 isolated from wine

BACKGROUND

Biogenic amines are molecules with allergenic properties. They are found in fermented products and are synthesized by lactic acid bacteria through the decarboxylation of amino acids present in the food matrix. The concentration of biogenic amines in fermented foodstuffs is influenced by many environmental factors, and in particular, biogenic amine accumulation depends on the quantity of available precursors. Enological practices which lead to an enrichment in nitrogen compounds therefore favor biogenic amine production in wine. Free amino acids are the only known precursors for the synthesis of biogenic amines, and no direct link has previously been demonstrated between the use of peptides by lactic acid bacteria and biogenic amine synthesis.

RESULTS

Here we demonstrate for the first time that a Lactobacillus plantarum strain isolated from a red wine can produce the biogenic amine tyramine from peptides containing tyrosine. In our conditions, most of the tyramine was produced during the late exponential growth phase, coinciding with the expression of the tyrDC and tyrP genes. The DNA sequences of tyrDC and tyrP in this strain share 98% identity with those in Lactobacillus brevis consistent with horizontal gene transfer from L. brevis to L. plantarum.

CONCLUSION

Peptides amino acids are precursors of biogenic amines for Lactobacillus plantarum strain IR BL0076.

Improved acid stress survival of Lactococcus lactis expressing the histidine decarboxylation pathway of Streptococcus thermophilus CHCC1524

Degradative amino acid decarboxylation pathways in bacteria generate secondary metabolic energy and provide resistance against acid stress. The histidine decarboxylation pathway of Streptococcus thermophilus CHCC1524 was functionally expressed in the heterologous host Lactococcus lactis NZ9000, and the benefits of the newly acquired pathway for the host were analyzed. During growth in M17 medium in the pH range of 5-6.5, a small positive effect was observed on the biomass yield in batch culture, whereas no growth rate enhancement was evident. In contrast, a strong benefit for the engineered L. lactis strain was observed in acid stress survival. In the presence of histidine, the pathway enabled cells to survive at pH values as low as 3 for at least 2 h, conditions under which the host cells were rapidly dying. The flux through the histidine decarboxylation pathway in cells grown at physiological pH was under strict control of the electrochemical proton gradient (pmf) across the membrane. Ionophores that dissipated the membrane potential (ΔΨ) and/or the pH gradient (ΔpH) strongly increased the flux, whereas the presence of glucose almost completely inhibited the flux. Control of the pmf over the flux was exerted by both ΔΨ and ΔpH and was distributed over the transporter HdcP and the decarboxylase HdcA. The control allowed for a synergistic effect between the histidine decarboxylation and glycolytic pathways in acid stress survival. In a narrow pH range around 2.5 the synergism resulted in a 10-fold higher survival rate.

The tyrosyl-tRNA synthetase like gene located in the tyramine biosynthesis cluster of Enterococcus durans is transcriptionally regulated by tyrosine concentration and extracellular pH

Background

The tyramine producer Enterococcus durans IPLA655 contains all the necessary genes for tyramine biosynthesis, grouped in the TDC cluster. This cluster includes tyrS, an aminoacyl-tRNA synthetase like gene.

Results

This work shows that tyrS was maximally transcribed in absence of tyrosine at acidic pH, showing a greater than 10-fold induction in mRNA levels over levels occurring in presence of tyrosine. Mapping of the tyrS transcriptional start site revealed an unusually long untranslated leader region of 322 bp, which displays the typical features of the T box transcriptional attenuation mechanism. The tyrosine concentration regulation of tyrS was found to be mediated by a transcription antitermination system, whereas the specific induction at acidic pH was regulated at transcription initiation level.

Conclusions

The expression of the tyrS gene present in the TDC cluster of E. durans is transcriptionally regulated by tyrosine concentration and extracelular pH. The regulation is mediated by both an antitermination system and the promoter itself.