Biomedical subjects

Arjan Narbad

Publications and source records attributed to Arjan Narbad.

6 recordsLinked to original sources

PubMed2004

Controlled expression of CluA in Lactococcus lactis and its role in conjugation.

CluA is a 136 kDa surface-bound protein encoded by the chromosomally located sex factor of Lactococcus lactis MG1363 and is associated with cell aggregation linked to high-frequency transfer of the sex factor. To further investigate the involvement of CluA in these phenomena, the cluA gene was cloned on a plasmid, downstream from the lactococcal nisA promoter. In a sex-factor-negative MG1363 derivative, nisin-controlled CluA expression resulted in aggregation, despite the absence of the other genes of the sex factor. Therefore, CluA is the only sex factor component responsible for aggregation. The direct involvement of CluA in the establishment of cell-to-cell contact for aggregate formation was observed by electron microscopy using immunogold-labelled CluA antibodies. Inactivation of cluA in an MG1363 background led to a dramatic decrease in sex factor conjugation frequency compared to the parental strain. Increasing levels of CluA expressed in trans in the cluA-inactivated donor strain facilitated a gradual restoration of conjugation frequency, reaching that of the parental strain. In conclusion, CluA is essential for efficient sex factor transfer in conjugation of L. lactis.

Animals↗

PubMed2004

The potential application of vanillin in preventing yeast spoilage of soft drinks and fruit juices.

The preservative effect of vanillin, the major constituent of vanilla beans, was studied in an apple juice and peach-flavored soft drink. Vanillin activity was tested against Saccharomyces cerevisiae and Candida parapsilosis at 8 and 25 degrees C over an 8-week storage period. Initial results in laboratory media indicated minimum inhibitory concentration values of 17 and 9 mM vanillin for the two yeast strains. Concentrations of 20 and 10 mM vanillin, respectively, were required to achieve complete inhibition of both yeast strains inoculated at a level of approximately 10(4) CFU/ml in the apple juice and peach-flavored soft drink over the 8-week storage at 25 degrees C. These effective levels were reduced to 5 and 1 mM, when the storage temperature was reduced to 8 degrees C. A biocidal effect against both yeasts was observed within 96 h to 8 weeks, with vanillin concentrations of 5 to 40 mM depending on the beverage and the storage temperatures used. The increased activity of vanillin in the peach-flavored soft drink (pH 3.1) in comparison to the apple juice (pH 3.5) is probably a result of the lower intrinsic pH of the former; however, variation in vitamin and mineral levels or the presence of other phenolic compounds between the two drinks might also have contributed to the observed differences. Furthermore, the increased activity at the lower temperature could be linked to the combination of the increased membrane fluidity and the membrane-perturbing action of vanillin. We conclude that vanillin has the potential to preserve fruit juices and soft drinks that are low in both lipid and protein content against S. cerevisiae and C. parapsilosis.

Benzaldehydes↗

PubMed2003

Analysis of the inhibition of food spoilage yeasts by vanillin.

The antimicrobial potential of vanillin, the major component of vanilla flavour, was examined against the growth of three yeasts associated with food spoilage, Saccharomyces cerevisiae, Zygosaccharomyces bailii and Zygosaccharomyces rouxii. Minimum inhibitory concentration (MIC) values of 21, 20 and 13 mM vanillin were determined for the three yeast strains, respectively. The observed inhibition was found to be biostatic. During fermentation, the bioconversion of sub-MIC levels of vanillin in the culture medium was demonstrated. The major bioconversion product was identified as vanillyl alcohol, however low levels of vanillic acid were also detected. Neither the vanillyl alcohol nor the vanillic acid was found to be antagonistic to yeast cell growth. The results indicate the importance of the aldehyde moiety in the vanillin structure regarding its antimicrobial activity and that the bioconversion of vanillin could be advantageous for the yeasts, but only at levels below MIC. These bioconversion activities, presumably catalysed by non-specific dehydrogenases, were shown to be expressed constitutively. It was observed that increased vanillin concentrations inhibited its own bioconversion suggesting that the activity required intact cells with metabolic capacity.

Antifungal Agents↗

PubMed2003

Vanillin.

Vanillin (4-hydroxy-3-methoxybenzaldehyde) is an important flavour and aroma molecule, but is also of interest because of its biogenetic relationship to the phenylpropanoid pathway and to other molecules of physiological significance, notably salicylate. Recent progress towards characterisation of the biosynthesis of vanillin is reviewed. In Vanilla, there is some evidence that the route to vanillin-beta-D-glucoside may proceed from 4-coumaric acid via 4-hydroxybenzaldehyde, with glucoside formation occurring not necessarily as the final step, and possibly with the involvement of 4-hydroxybenzyl alcohol beta-D-glucoside tartrate bis-esters as "shunt" metabolites. This appears to be given tentative support by the recent partial characterisation of a 4-hydroxybenzaldehyde synthase from Vanilla. On the other hand, a well-characterised, CoA-dependent, non-oxidative chain-shortening mechanism to produce vanillin from ferulic acid, occurring as part of a pathway of hydroxycinnamate degradation in Pseudomonas, may not be representative of hydroxycinnamate chain-shortening mechanism(s) occurring in Vanilla and other plants. Nevertheless, by expression of the Pseudomonas enzyme 4-hydroxycinnamoyl-CoA hydratase/lyase (HCHL), attempts have been made to introduce a direct capacity for vanillin formation into model plants by diversion of the phenylpropanoid pathway. The results obtained have emphasised the obstacles to achieving the desired oxidation level (aldehyde) and ring substitution (4-hydroxy-3-methoxyphenyl), even when a substantial metabolic diversion is successfully achieved. Finally, the significance of the latest biosynthetic and biotechnological developments is reviewed briefly in relation to authentication of vanillin.

Benzaldehydes↗

PubMed2002

4-Hydroxycinnamoyl-CoA hydratase/lyase, an enzyme of phenylpropanoid cleavage from Pseudomonas, causes formation of C(6)-C(1) acid and alcohol glucose conjugates when expressed in hairy roots of Datura stramonium L.

4-Hydroxycinnamoyl-CoA hydratase/lyase (HCHL), a crotonase homologue of phenylpropanoid catabolism from Pseudomonas fluorescens strain AN103, led to the formation of 4-hydroxybenzaldehyde metabolites when expressed in hairy root cultures of Datura stramonium L. established by transformation with Agrobacterium rhizogenes. The principal new compounds observed were the glucoside and glucose ester of 4-hydroxybenzoic acid, together with 4-hydroxybenzyl alcohol- O-beta- D-glucoside. In lines actively expressing HCHL, these together amounted to around 0.5% of tissue fresh mass. No protocatechuic derivatives were found, although a trace of vanillic acid-beta- D-glucoside was detected. There was no accumulation of 4-hydroxybenzaldehydes, whether free or in the form of their glucose conjugates. There was some evidence suggesting a diminished availability of feruloyl-CoA for the production of feruloyl putrescine and coniferyl alcohol. The findings are discussed in the context of a diversion of phenylpropanoid metabolism, and the ability of plants and plant cultures to conjugate phenolic compounds.

Benzaldehydes↗

PubMed1998

Metabolism of ferulic acid via vanillin using a novel CoA-dependent pathway in a newly-isolated strain of Pseudomonas fluorescens.

A soil bacterium, designated Pseudomonas fluorescens AN103, was isolated based on its ability to grow on ferulic acid as a sole source of carbon and energy. In addition, this strain was found to metabolize a number of related phenolic substrates which contained a hydroxyl group at the para position of the aromatic ring. During growth on ferulic acid, transient accumulation of vanillic acid and trace amounts of protocatechuic acid were detected in the culture medium. Washed cells grown on ferulic acid readily oxidized vanillin, vanillic acid and protocatechuic acid, the three putative intermediates of the metabolic pathway. The side-chain cleavage of ferulic acid to produce vanillin was demonstrated in vitro for the first time and this enzyme-catalysed reaction was shown to have an essential requirement for CoASH, ATP and MgCl2. This conversion involved a two-step process involving a CoA ligase followed by the side-chain cleavage. The addition of NAD increased the oxidation of vanillin to vanillic acid and had an overall effect of increasing the rate of ferulic acid cleavage. The application of 13C-NMR studies in vitro revealed acetyl-CoA as the C2 side-chain cleavage product. High levels of inducible ferulate-CoA ligase and NAD-linked vanillin dehydrogenase were detected and a novel pathway for ferulic acid metabolism in this organism is proposed.

Aldehyde Oxidoreductases↗