Wine phenolic compounds influence the production of volatile phenols by wine-related lactic acid bacteria

Aims: To evaluate the effect of wine phenolic compounds on the production of volatile phenols (4‐vinylphenol [4VP] and 4‐ethylphenol [4EP]) from the metabolism of p‐coumaric acid by lactic acid bacteria (LAB). Methods and Results: Lactobacillus plantarum, Lactobacillus collinoides and Pediococcus pentosaceus were grown in MRS medium supplemented with p‐coumaric acid, in the presence of different phenolic compounds: nonflavonoids (hydroxycinnamic and benzoic acids) and flavonoids (flavonols and flavanols). The inducibility of the enzymes involved in the p‐coumaric acid metabolism was studied in resting cells. The hydroxycinnamic acids tested stimulated the capacity of LAB to synthesize volatile phenols. Growth in the presence of hydroxycinnamic acids, especially caffeic acid, induced the production of 4VP by resting cells. The hydroxybenzoic acids did not significantly affect the behaviour of the studied strains. Some of the flavonoids showed an effect on the production of volatile phenols, although strongly dependent on the bacterial species. Relatively high concentrations (1 g l^?1) of tannins inhibited the synthesis of 4VP by Lact. plantarum. Conclusions: Hydroxycinnamic acids were the main compounds stimulating the production of volatile phenols by LAB. The results suggest that caffeic and ferulic acids induce the synthesis of the cinnamate decarboxylase involved in the metabolism of p‐coumaric acid. On the other hand, tannins exert an inhibitory effect. Significance and Impact of the Study: This study highlights the capacity of LAB to produce volatile phenols and that this activity is markedly influenced by the phenolic composition of the medium.     

Biodegradation of phenolic compounds by sulfate-reducing bacteria from contaminated sediments

The biodegradation of phenolic compounds under sulfate-reducing conditions was studied in sediments from northern Indiana. Phenol, p-cresol and 4-chlorophenol were selected as test substrates and added to sediment suspensions from four sites at an initial concentration of 10 mg/liter. Degradative abilities of the sediment microorganisms from the four sites could be related to previous exposure to phenolic pollution. Time to onset of biodegradation of p-cresol and phenol in sediment suspensions from a nonindustrialized site was approximately 70 and 100 days, respectively, in unacclimated cultures. In sediment slurries from three sites with a history of wastewater discharges containing phenolics, time to onset of biodegradation was 50–70 days for p-cresol and 50–70 days for phenol in unacclimated cultures. In acclimated cultures from all four sites, the length of the lag phase was reduced to 14–35 days for p-cresol and 25–60 days for phenol. Length of the biodegradative phase varied from 25 to 40 days for phenol and 10 to 50 days for p-cresol and was not markedly affected by acclimation. Substrate mineralization by sulfate-reducing bacteria was confirmed with radiotracer techniques using an acclimated sediment culture from one site. Addition of molybdate, a specific inhibitor of sulfate reduction, and bacterial cell inactivation inhibited sulfate reduction and substrate utilization. None of the sites exhibited the ability to degrade 4-chlorophenol, nor were acclimated phenol and p-cresol degrading cultures from a particular site able to cometabolize 4-chlorophenol.Correspondence to: D. Dean-Ross     

Inactivation of oenological lactic acid bacteria (Lactobacillus hilgardii and Pediococcus pentosaceus) by wine phenolic compounds

Aims:  To investigate the inactivation properties of different classes of phenolic compounds present in wine against two wine isolates of Lactobacillus hilgardii and Pediococcus pentosaceus , and to explore their inactivation mechanism.
Methods and Results:  After a first screening of the inactivation potency of 21 phenolic compounds (hydroxybenzoic and hydroxycinnamic acids, phenolic alcohols, stilbenes, flavan-3-ols and flavonols) at specific concentrations, the survival parameters (MIC and MBC) of the most active compounds were determined. For the L. hilgardii strain, the flavonols morin and kaempferol showed the strongest inactivation (MIC values of one and 5 mg l⁻¹, and MBC values of 7·5 and 50 mg l⁻¹, respectively). For the P. pentosaceus strain, flavonols also showed the strongest inactivation effects, with MIC values between one and 10 mg l⁻¹ and MBC values between 7·5 and 300 mg l⁻¹. Observations by epifluorescence and scanning electron microscopy revealed that the phenolics damaged the cell membrane and promoted the subsequent release of the cytoplasm material into the medium.
Conclusions:  The antibacterial activity of wine phenolics against L. hilgardii and P. pentosaceus was dependent on the phenolic compound tested, and led not only to bacteria inactivation, but also to the cell death.
Significance and Impact of the Study:  New information about the inactivation properties of wine lactic acid bacteria by phenolic compounds is presented. It opens up a new area of study for selecting/obtaining wine phenolic preparations with potential applications as a natural alternative to SO₂ in winemaking.     

Transformation of chlorinated phenolic compounds in the genusRhodococcus

The ability of strains of the genusRhodococcus to transform chlorinated phenolic compounds was studied. Noninduced cells of several strains ofRhodococcus, covering at least eight species, were found to attack mono-, di-, and trichlorophenols by hydroxylation at theortho position to chlorocatechols. 3-chlorophenol and 4-chlorophenol were converted to 4-chlorocatechol, 2,3-dichlorophenol to 3,4-dichlorocatechol, and 3,4-di-chlorophenol to 4,5-dichlorocatechol. The chlorocatechols accumulated to nearly stoichiometric amounts. Other mono- and dichlorophenols were not transformed. The ability of the strains to hydroxylate chlorophenols correlated with the ability to grow on unsubstituted phenol as the sole source of carbon and energy. SeveralRhodococcus strains attacked chlorophenolic compounds by both hydroxylation and O-methylation. 2,3,4-, 2,3,5- and 3,4,5-trichlorophenol were hydroxylated to trichlorocatechol and then sequentially O-methylated to chloroguaiacol and chloroveratrole. Tetrachlo-rohydroquinone was O-methylated sequentially to tetrachloro-4-methoxy-phenol and tetrachloro-1,4-dimethoxybenzene. Several of the active strains had no known history of exposure to any chloroaromatic compound. Rhodococci are widely distributed in soil and sludge and these results suggest that this genus may play an important role in transformation of chlorinated phenolic compounds in the environment.     

Freeze-dried recombinant bacteria for on-site detection of phenolic compounds by color change

We herein report the development of a recombinant bacterial biosensor for the rapid and easy detection of phenolic compounds in the field. A plasmid was designed to encode a beta-galactosidase reporter gene under the control of capR, an activator involved in phenolic compound degradation. The construct was transformed into Escherichia coli, and transformed cells were stored after being freeze-dried in the presence of sucrose. For detection of phenolic compounds, the cells were rehydrated, and used instantly, without any growth step. In the presence of 0.1 microM-10mM phenol, we observed a red color from hydrolysis of chlorophenol red beta-D-galactopyranoside (CPRG) or an indigo color from hydrolysis of X-galactopyranoside (X-gal). Other phenolic compounds could be detected by this system, including catechol, 2-methylphenol, 2-chlorophenol, 3-methylphenol, 2-nitrophenol, and 4-chlorophenol. These results suggest that this novel bacteria biosensor may be useful for easy, on-site detection of phenolic compounds without the need for unwieldy equipment or sample pretreatment. Indeed, biosensor systems involving beta-galactosidase-expressing freeze-dried recombinant bacteria could prove useful for the in situ detection of many more compounds in the future.     

Influence of various soil factors on the effects of ferulic acid on leaf expansion of cucumber seedlings

Summary Cucumber seedlings were grown in a Portsmouth soil-sand system to study how varying soil clay and organic matter content might modify cucumber seedling response to ferulic acid, a reported allelopathic agent. Leaf area expansion of cucumber seedlings, soil respiration, and soil solution concentrations of ferulic acid were monitored. Leaf area, mean absolute rates of leaf expansion, and shoot dry weight of cucumber seedlings were significantly reduced by ferulic acid concentrations ranging from 10 to 70 μg/g dry soil. Ferulic acid was applied every other day, since it rapidly disappeared from soil solution as a result of retention by soil particles, utilization by microbes and/or uptake by roots. The amount of ferulic acid retained (i.e., adsorbed, polymerized,etc.) by soil particles appeared to be secondary to microbial utilization and/or uptake by roots. Varying clay (5.3 to 9.8 g/cup) and organic matter (2.0 to 0.04g/cup) contents of the soil appeared to have little impact on the disappearance of ferulic acid from soil solution under “ideal” growth conditions for cucumber seedlings unless larger amounts of ferulic acid were added to the soil; in this case 200 μg/g. The addition of ferulic acid to the soil materials substantially increased the activity of the soil microbes. This latter conclusion is based on recovery of ferulic acid from soil solution and soil respiration measurements. Paper No. 10347 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh, N C 27695-7601. The use of trade names in this publication does not imply endorsement by the North Carolina Agricultural Research Service of the product named, nor criticism of similar ones not mentioned.     

Biotransformation of ferulic acid and related compounds by mutant strains of Pseudomonas fluorescens

Pseudomonas fluorescens strain FE2 isolated in the presence of ferulic acid was able to grow on hydroxylated and methoxylated compounds bearing the hydroxyl group in the para position. By ethylmethansulphonate (EMS) and transposon mutagenesis, mutants unable to utilize ferulic acid have been selected. The metabolic characterization of the wild-type strain and its mutants indicates that ferulic acid was degraded through the formation of vanillic acid. Mutant FE2B in co-oxidation experiments with glutamate, is able to transform ferulic and dihydroferulic acid into vanillic acid, 4-hydroxycinnamic acid and 3 (4-hydroxyphenyl)-propanoic acid into 4-hydroxybenzoic acid, and 3-hydroxycinnamic acid into 3-hydroxybenzoic acid. The bioconversion of hydroxylated aromatic substrates by the FE2B mutants suggests that the presence of a hydroxyl group on the aromatic ring is required for deacetylase activity.     

Antibacterial activity of sphagnum acid and other phenolic compounds found in Sphagnum papillosum against food-borne bacteria

Aims:  To identify the phenolic compounds in the leaves of Sphagnum papillosum and examine their antibacterial activity at pH appropriate for the undissociated forms.
Methods and Results:  Bacterial counts of overnight cultures showed that whilst growth of Staphylococcus aureus 50084 was impaired in the presence of milled leaves, the phenol-free fraction of holocellulose of S. papillosum had no bacteriostatic effect. Liquid chromatography–mass spectrometry analysis of an acetone–methanol extract of the leaves detected eight phenolic compounds. Antibacterial activity of the four dominating phenols specific to Sphagnum leaves, when assessed in vitro as minimal inhibitory concentrations (MICs), were generally >2·5 mg ml⁻¹. MIC values of the Sphagnum- specific compound 'sphagnum acid' [ p -hydroxy-β-(carboxymethyl)-cinnamic acid] were >5 mg ml⁻¹. No synergistic or antagonistic effects of the four dominating phenols were detected in plate assays.
Conclusions:  Sphagnum -derived phenolics exhibit antibacterial activity in vitro only at concentrations far in excess of those found in the leaves.
Significance and Impact of the Study:  We have both identified the phenolic compounds in S. papillosum and assessed their antibacterial activity. Our data indicate that phenolic compounds in isolation are not potent antibacterial agents and we question their potency against food-borne pathogens.     

Effects of phenolic compounds on reactions involving various organic radicals

Investigation of effects produced by 26 various phenol and diphenol derivatives, including industrial and natural antioxidants (ionol, bis-phenol 2246, alpha-tocopherol), on final product yields of radiation-induced free-radical processes involving peroxyl, alkyl, alpha-hydroxyalkyl and alpha,beta-dihydroxyalkyl radicals has been performed. Ionol and bis-phenol 2246 have been shown to be more effective than alpha-tocopherol or diphenol derivatives in suppressing hydrocarbon oxidation processes. At the same time, alpha-tocopherol and its water-soluble analogues, as well as diphenol-based substances, are more effective than phenol derivatives in regulating various homolytic processes involving carbon-centered radicals. This fact can be accounted for by taking into consideration the contribution to formation of the final product set and the respective yields made by semiquinone radicals and compounds with quinoid structure arising in the course of homolytic transformations in systems containing diphenol derivatives.     

Biodegradation of diphenylarsinic acid to arsenic acid by novel soil bacteria isolated from contaminated soil

Microorganisms capable of degrading diphenylarsinic acid (DPAA) were enriched from contaminated soil using the soil-charcoal perfusion method. Two novel bacterial strains, L2406 and L2413, that can degrade DPAA in a mineral salt medium supplemented with DPAA as the sole carbon source were isolated. Based on comparative morphology, physiology, and comparison of the 16S rRNA gene sequences, both were presumed to be species closely related to Ensifer adhaerens. As the metabolites, phenylarsonic acid (PAA) was determined by liquid chromatography-mass spectrometry analysis as well as three unknown peaks all of whose molecular weights were estimated to be 278. The increase of m/z = 16 from DPAA in the unknowns suggests monohydroxylation of DPAA at the 2-, 3- and 4-positions. The ability of strains L2406 and L2413 to degrade DPAA was suppressed in iron insufficient conditions, e.g. less than 7.2 μM iron in the culture medium. These facts strongly suggest the following hypothesis: Monooxygenase works at the initial degradation step of DPAA degradation by the isolates; and direct hydrolysis from DPAA to PAA is not likely to occur. In addition, release of arsenic acid from PAA by strain L2406 was confirmed by liquid chromatography-inductively coupled plasma mass spectrometry. From these results, strain L2406 was considered to be capable of degrading DPAA to arsenic acid via PAA when DPAA was supplied as the sole carbon source.