Antimicrobial properties and mechanism of volatile isoamyl acetate, a main flavour component of Japanese sake (Ginjo-shu)

Tracing the volatilomic fingerprint of grape pomace as a powerful approach for its valorization

The huge amount of grape pomace (GP) generated every year worldwide, particularly in Europe, creates negative impacts at the economic and environmental levels. As far as we know, scarce research has been done on the volatilomic fingerprint of GP. To meet consumer demand for healthy foods, there is a growing interest in the characterization of particular volatile organic metabolites (VOMS) in GP that can be used for industrial applications, including the food industry. In this study, the volatilomic fingerprint of GP obtained from different Vitis vinifera L. grapes was established by solid phase microextraction (HS-SPME) combined to gas chromatography-mass spectrometry (GC-MS), to explore the properties of most dominant VOMs in a context of its application on marketable products. A total of 52 VOMs belonging to different chemical families were identified. Alcohols, carbonyl compounds, and esters, are the most dominant, representing 38.8, 29.3, and 24.2% of the total volatile profile of the investigated GP, respectively. Esters (e.g., isoamyl acetate, hexyl acetate, ethyl hexanoate) and alcohols (e.g., 3-methyl butan-2-ol, hexan-1-ol) can be used as flavoring agents with potential use in the food industry, and in the cosmetic industry, for fragrances production. In addition, the identified terpenoids (e.g., menthol, ylangene, limonene) exhibit antioxidant, antimicrobial, and anticancer, biological properties, among others, boosting their potential application in the pharmaceutical industry. The obtained results revealed the potential of some VOMs from GP to replace synthetic antioxidants, colorants, and antimicrobials used in the food industry, and in the cosmetic and pharmaceutical industry, meeting the increasing consumer demand for natural alternative compounds.

Early detection of Botrytis cinerea in strawberry fruit during quiescent infection using selected ion flow tube mass spectrometry (SIFT-MS)

Botrytis cinerea is a devastating pathogen that can cause huge postharvest losses of strawberry. Although this fungus usually infects strawberries through their flowers, symptoms mainly appear when fruit are fully mature. A fast and sensitive method to detect and quantify the fungal infection, prior to symptom development, is, therefore, needed. In this study, we explore the possibility of using the strawberry volatilome to identify biomarkers for B. cinerea infection. Strawberry flowers were inoculated with B. cinerea to mimic the natural infection. First, quantitative polymerase chain reaction (qPCR) was used to quantify B. cinerea in the strawberry fruit. The detection limit of qPCR for B. cinerea DNA extracted from strawberries was 0.01 ng. Subsequently, changes in the fruit volatilome at different fruit developmental stages were characterized using gas chromatography - mass spectrometry (GC-MS) and selected ion flow tube mass spectrometry (SIFT-MS). Based on GC-MS data, 1-octen-3-ol produced by B. cinerea was confirmed as a potential biomarker of B. cinerea infection. Moreover, the product ion NO⁺ 127, obtained by SIFT-MS measurements, was proposed as a potential biomarker for B. cinerea infection by comparing its relative level with that of 1-octen-3-ol (obtained by GC-MS) and B. cinerea (obtained by qPCR). Separate PLS regressions were carried out for each developmental stages, and 11 product ions were significantly altered at all developmental stages. Finally, PLS regressions using these 11 ions as variables allowed the discrimination between samples containing different amount of B. cinerea. This work showed that profiling the fruit's volatilome using SIFT-MS can be used as a potential alternative to detect B. cinerea during the quiescent stage of B. cinerea infection prior to symptom development. Moreover, the corresponding compounds of potential biomarkers suggest that the volatile changes caused by B. cinerea infection may contribute to strawberry defense.

Repurposing of phyto-ligand molecules from the honey bee products for Alzheimer's disease as novel inhibitors of BACE-1: small molecule bioinformatics strategies as amyloid-based therapy

Alzheimer's disease (AD) is one of the neurodegenerative diseases, manifesting dementia, spatial disorientation, language, cognitive, and functional impairment, mainly affects the elderly population with a growing concern about the financial burden on society. Repurposing can improve the traditional progress of drug design applications and could speed up the identification of innovative remedies for AD. The pursuit of potent anti-BACE-1 drugs for AD treatment has become a pot boiler topic in the recent past and to instigate the design of novel improved inhibitors from the bee products. Drug-likeness characteristics (ADMET: absorption, distribution, metabolism, excretion, and toxicity), docking (AutoDock Vina), simulation (GROMACS), and free energy interaction (MM-PBSA, molecular mechanics Poisson-Boltzmann surface area) analyses were performed to identify the lead candidates from the bee products (500 bioactives from the honey, royal jelly, propolis, bee bread, bee wax, and bee venom) for Alzheimer's disease as novel inhibitors of BACE-1 (beta-site amyloid precursor protein cleaving enzyme (1) receptor using appropriate bioinformatics tools. Forty-four bioactive lead compounds were screened from the bee products through high throughput virtual screening on the basis of their pharmacokinetic and pharmacodynamics characteristics, showing favorable intestinal and oral absorption, bioavailability, blood brain barrier penetration, less skin permeability, and no inhibition of cytochrome P450 inhibitors. The docking score of the forty-four ligand molecules was found to be between -4 and -10.3 kcal/mol, respectively, exhibiting strong binding affinity to BACE1 receptor. The highest binding affinity was observed in the rutin (-10.3 kcal/mol), 3,4-dicaffeoylquinic acid (-9.5 kcal/mol), nemorosone (-9.5 kcal/mol), and luteolin (-8.9 kcal/mol). Furthermore, these compounds demonstrated high total binding energy -73.20 to -105.85 kJ/mol), and low root mean square deviation (0.194-0.202 nm), root mean square fluctuation (0.0985-0.1136 nm), radius of gyration (2.12 nm), number of H-bonds (0.778-5.436), and eigenvector values (2.39-3.54 nm²) in the molecular dynamic simulation, signifying restricted motion of Cα atoms, proper folding and flexibility, and highly stable with compact of the BACE1 receptor with the ligands. Docking and simulation studies concluded that rutin, 3,4-dicaffeoylquinic acid, nemorosone, and luteolin are plausibly used as novel inhibitors of BACE1 to combat AD, but further in-depth experimental investigations are warranted to prove these in silico findings.

Optimization of green and environmentally-benign synthesis of isoamyl acetate in the presence of ball-milled seashells by response surface methodology

Ball-milled seashells, as a nano-biocomposite catalyst and natural source of CaCO₃ in its aragonite microcrystalline form with fixed CO₂, was optimized for the synthesis of isoamyl acetate (3-methylbutyl ethanoate) by response surface methodology with a five-level three-factor rotatable circumscribed central composite design. The seashells nano-biocomposite has proved to be an excellent heterogeneous multifunctional catalyst for the green and environmentally-benign synthesis of isoamyl acetate from acetic acid and isoamyl alcohol under solvent-free conditions. A high yield of 91% was obtained under the following optimal conditions: molar ratio of alcohol: acetic acid (1:3.7), catalyst loading (15.7 mg), the reaction temperature (98 °C), and the reaction time (219 min). The outstanding advantages of this protocol are the use of an inexpensive, naturally occurring and easily prepared nano-biocomposite material having appropriate thermal stability and without any modifications using hazardous reagents, lower catalyst loading and reaction temperature, no use of corrosive Bronsted acids as well as toxic azeotropic solvents or water adsorbents, and simplicity of the procedure.

Assessing the Various Antagonistic Mechanisms of Trichoderma Strains against the Brown Root Rot Pathogen Pyrrhoderma noxium Infecting Heritage Fig Trees

A wide range of phytopathogenic fungi exist causing various plant diseases, which can lead to devastating economic, environmental, and social impacts on a global scale. One such fungus is Pyrrhoderma noxium, causing brown root rot disease in over 200 plant species of a variety of life forms mostly in the tropical and subtropical regions of the globe. The aim of this study was to discover the antagonistic abilities of two Trichoderma strains (#5001 and #5029) found to be closely related to Trichoderma reesei against P. noxium. The mycoparasitic mechanism of these Trichoderma strains against P. noxium involved coiling around the hyphae of the pathogen and producing appressorium like structures. Furthermore, a gene expression study identified an induced expression of the biological control activity associated genes in Trichoderma strains during the interaction with the pathogen. In addition, volatile and diffusible antifungal compounds produced by the Trichoderma strains were also effective in inhibiting the growth of the pathogen. The ability to produce Indole-3-acetic acid (IAA), siderophores and the volatile compounds related to plant growth promotion were also identified as added benefits to the performance of these Trichoderma strains as biological control agents. Overall, these results show promise for the possibility of using the Trichoderma strains as potential biological control agents to protect P. noxium infected trees as well as preventing new infections.

Effect of Dough-Related Parameters on the Antimold Activity of Wickerhamomyces anomalus Strains and Mold-Free Shelf Life of Bread

The aim of the present study was to assess the antimold capacity of three Wickerhamomyces anomalus strains, both in vitro and in situ, and to identify the responsible volatile organic compounds. For that purpose, two substrates were applied; the former included brain heart infusion broth, adjusted to six initial pH values (3.5, 4.0, 4.5, 5.0, 5.5, 6.0) and supplemented with six different NaCl concentrations (0.0%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%), while the latter was a liquid dough, fortified with the six aforementioned NaCl concentrations. After a 24 h incubation at 30 °C, the maximum antimold activity was quantified for all strains at 5120 AU/mL, obtained under different combinations of initial pH value and NaCl concentration. A total of twelve volatile compounds were detected; ethanol, ethyl acetate, isoamyl alcohol and isoamyl acetate were produced by all strains. On the contrary, butanoic acid-ethyl ester, acetic acid-butyl ester, ethyl caprylate, 3-methyl-butanoic acid, 2,4-di-tert-butyl-phenol, benzaldehyde, nonanal and octanal were occasionally produced. All compounds exhibited antimold activity; the lower MIC was observed for 2,4-di-tert-butyl-phenol and benzaldehyde (0.04 and 0.06 μL/mL of headspace, respectively), while the higher MIC was observed for butanoic acid-ethyl ester and ethyl caprylate (5.14 and 6.24 μL/mL of headspace, respectively). The experimental breads made with W. anomalus strains LQC 10353, 10346 and 10360 gained an additional period of 9, 10 and 30 days of mold-free shelf life, compared to the control made by commercially available baker’s yeast. Co-culture of the W. anomalus strains with baker’s yeast did not alter the shelf-life extension, indicating the suitability of these strains as adjunct cultures.

Mezcal as a Novel Source of Mixed Yeasts Inocula for Wine Fermentation

Mezcal yeasts were evaluated for their potential as grape-juice fermenters, characterizing their fermentation performance, both in terms of primary and volatile metabolites. Experiments were first carried-out in a semi-synthetic medium and then on grape juice, and population dynamics of the chosen mixed inoculum was assessed in grape juice. Accordingly, we initially tested 24 mezcal yeasts belonging to ten different species, and chose those that were more productive and stress tolerant for the mixed (dual) inoculum, having a final selection of three Saccharomyces cerevisiae strains (plus Fermichamp, a commercial wine strain) and three non-Saccharomyces strains, belonging to Kluyveromyces marxianus, Torulaspora delbrueckii, and Zygosaccharomyces bailii species. For the combination S. cerevisiae/T. delbrueckii (Sc/Td) mixed inoculum, we observed increasing isoamyl alcohol and phenyl ethyl acetate concentrations, as compared with the use of individual Saccharomyces strains, which resulted in a fruitier aroma profile. Alcohol final concentration was in average lower for the Sc/Td inoculum (fermentation power, FP, 13.6) as compared with the individual mezcal Saccharomyces strains (FP 14.3), and it was the highest when Td was co-cultured with the commercial strain (FP 14.6). Overall, our results show the feasibility of using yeasts isolated from mezcal as a novel source of inoculum for wine-type fermentation.

Antifungal activity of volatile compounds produced by endophytic Bacillus subtilis DZSY21 against Curvularia lunata

Purpose

To screen endophytic Bacillus producing volatile organic compounds (VOCs) with antifungal activity, and to explore their biocontrol properties toward the growth and pathogenicity of Curvularia lunata.

Methods

Two-sealed-base-plate assays were used to estimate the antifungal activities of Bacillus strains against C. lunata. Conjoint analysis of solid-phase microextraction gas chromatography-mass spectrometry and antagonistic experiments were used to identify the VOCs responsible for the antifungal activity. Effects of individual synthetic VOCs were analyzed along with reactive oxygen species (ROS) accumulation in C. lunata conidia. After exposure to individual VOCs, conidia were also sprayed onto maize leaves to evaluate their pathogenicity. Expression levels of virulence-related genes in C. lunata mycelium following exposure to VOCs were analyzed using quantitative real-time PCR.

Results

Among the ten endophytic Bacillus strains and two plant growth-promoting rhizobacterial (PGPR) strains, only B. subtilis strain DZSY21 strongly inhibited the growth of C. lunata by producing VOCs. 2-Methylbutyric acid, 2-heptanone, and isopentyl acetate produced by strain DZSY21 showed inhibitory effects on the mycelia growth and conidial sporulation of C. lunata. 2-Heptanone and isopentyl acetate also repressed the germination of conidia and the expression levels of virulence-related genes in C. lunata mycelium. Moreover, isopentyl acetate strongly enhanced the accumulation of intracellular ROS in conidia. The disease indexes of maize leaves sprayed with VOC-treated C. lunata conidia were reduced from 60.52 to 26.64%.

Conclusion

Endophytic B. subtilis strain DZSY21 displayed the potential to control C. lunata by producing VOCs, especially 2-heptanone and isopentyl acetate.

Volatile Compound-Mediated Recognition and Inhibition Between Trichoderma Biocontrol Agents and Fusarium oxysporum

Certain Trichoderma strains protect plants from diverse pathogens using multiple mechanisms. We report a novel mechanism that may potentially play an important role in Trichoderma-based biocontrol. Trichoderma virens and T. viride significantly increased the amount/activity of secreted antifungal metabolites in response to volatile compounds (VCs) produced by 13 strains of Fusarium oxysporum, a soilborne fungus that infects diverse plants. This response suggests that both Trichoderma spp. recognize the presence of F. oxysporum by sensing pathogen VCs and prepare for attacking pathogens. However, T. asperellum did not respond to any, while T. harzianum responded to VCs from only a few strains. Gene expression analysis via qPCR showed up-regulation of several biocontrol-associated genes in T. virens in response to F. oxysporum VCs. Analysis of VCs from seven F. oxysporum strains tentatively identified a total of 28 compounds, including six that were produced by all of them. All four Trichoderma species produced VCs that inhibited F. oxysporum growth. Analysis of VCs produced by T. virens and T. harzianum revealed the production of compounds that had been reported to display antifungal activity. F. oxysporum also recognizes Trichoderma spp. by sensing their VCs and releases VCs that inhibit Trichoderma, suggesting that both types of VC-mediated interaction are common among fungi.

Caenorhabditis elegans susceptibility to Daldinia cf. concentrica bioactive volatiles is coupled with expression activation of the stress-response transcription factor daf-16, a part of distinct nematicidal action

The bionematicidal effect of a synthetic volatile mixture (SVM) of four volatile organic compounds (VOCs) emitted by the endophytic fungus Daldinia cf. concentrica against the devastating plant-parasitic root-knot nematode Meloidogyne javanica has been recently demonstrated in both in vitro and greenhouse experiments. However, the mode of action governing the observed irreversible paralysis of J2 larvae upon exposure to SVM is unknown. To unravel the mechanism underlying the anthelmintic and nematicidal activities, we used the tractable model worm Caenorhabditis elegans. C. elegans was also susceptible to both the fungal VOCs and SVM. Among compounds comprising SVM, 3-methyl-1-butanol, (±)-2-methyl-1-butanol, and 4-heptanone showed significant nematicidal activity toward L1, L4 and young adult stages. Egg hatching was only negatively affected by 4-heptanone. To determine the mechanism underlying this activity, we examined the response of C. elegans mutants for glutamate-gated chloride channel and acetylcholine transporter, targets of the nematicidal drugs ivermectin and aldicarb, respectively, to 4-heptanone and SVM. These aldicarb- and ivermectin-resistant mutants retained susceptibility upon exposure to 4-heptanone and SVM. Next, we used C. elegans TJ356 strain zIs356 (daf-16::GFP+rol-6), LD1 ldIs7 [skn-1B/C::GFP + pRF4(rol-6(su1006))], LD1171 ldIs3 [gcs-1p::gfp; rol-6(su1006))], CL2166 dvIs19 (gst-4p::GFP) and CF1553 muIs84 (sod-3p::GFP+rol-6), which have mutations in genes regulating multiple stress responses. Following exposure of L4 larvae to 4-heptanone or SVM, there was clear nuclear translocation of DAF-16::GFP, and SKN-1::GFP indicating that their susceptibility involves DAF-16 and SKN1 regulation. Application of 4-heptanone, but not SVM, induced increased expression of, gcs-1::GFP and gst-4::GFP compared to controls. In contrast, application of 4-heptanone or SVM to the sod-3::GFP line elicited a significant decline in overall fluorescence intensity compared to controls, indicating SOD-3 downregulation and therefore overall reduction in cellular redox machinery. Our data indicate that the mode of action of SVM and 4-heptanone from D. cf. concentrica differs from that of currently available nematicides, potentially offering new solutions for nematode management.

Characterization and Synergistic Effect of Antifungal Volatile Organic Compounds Emitted by the Geotrichum candidum PF005, an Endophytic Fungus from the Eggplant

Plant-associated endophytes are recognized as sources of novel bioactive molecules having diverse applications. In this study, an endophytic yeast-like fungal strain was isolated from the fruit of eggplant (Solanum melongena) and identified as Geotrichum candidum through phenotypic and genotypic characterizations. This endophytic G. candidum isolate PF005 was found to emit fruity scented volatiles. The compositional profiling of volatile organic compounds (VOCs) revealed the presence of 3-methyl-1-butanol, ethyl 3-methylbutanoate, 2-phenylethanol, isopentyl acetate, naphthalene, and isobutyl acetate in significant proportion when analyzed on a time-course basis. The VOCs from G. candidum exhibited significant mycelial growth inhibition (54%) of phytopathogen Rhizoctonia solani, besides having mild antifungal activity against a few other fungi. The source of carbon as a nutrient was found to be an important factor for the enhanced biosynthesis of antifungal VOCs. The antifungal activity against phytopathogen R. solani was improved up to 91% by feeding the G. candidum with selective precursors of alcohol and ester volatiles. Furthermore, the antifungal activity of VOCs was enhanced synergistically up to 92% upon the exogenous addition of naphthalene (1.0 mg/plate). This is the first report of G. candidum as an endophyte emitting antifungal VOCs, wherein 2-penylethanol, isopentyl acetate, and naphthalene were identified as important contributors to its antifungal activity. Possible utilization of G. candidum PF005 as a mycofumigant has been discussed based upon its antifungal activity and the qualified presumption of safety status.

Antifungal, Mechanical, and Physical Properties of Edible Film Containing Williopsis saturnus var. saturnus Antagonistic Yeast

The molding of food products causing health risks is a main problem in the food industry. In this study, as an alternative solution for preventing mold growth, an antifungal edible film was developed by incorporating Williopsis saturnus var. saturnus (0; 3; 7; and 9 logs CFU/cm² ) into whey protein concentrate (WPC) based films. Antifungal properties of the films against Penicilium expansum and Aspergillus niger were analyzed using the disc diffusion method. Physical (barrier, solubility, color), mechanical (tensile strength and percent elongation) properties of the films as well as the survival of W. saturnus in the film were assessed during 28 days of storage at 23 °C. According to the results, the viability of W. saturnus (7 and 9 logs CFU/cm² ) in WPC films stored for 28 days under vacuum or non-vacuum decreased to 36% and 60%, respectively. In addition, films containing W. saturnus decreased the viability of P. expansum and A. niger by 29% and 19%, respectively. Adding yeast did not change the tensile strength (P > 0.05), but significantly decreased % elongation and increased water vapor and oxygen permeability and water solubility (P < 0.05). In conclusion, this study showed that the developed films may be useful for inhibiting mold growth on foods.

Antifungal peptidic compound from the deep-sea bacterium Aneurinibacillus sp. YR247

Aneurinibacillus: sp. YR247 was newly isolated from the deep-sea sediment inside the Calyptogena community at a depth of 1171 m in Sagami Bay. The strain exhibited antifungal activity against the filamentous fungus Aspergillus brasiliensis NBRC9455. A crude extract prepared from the YR247 cells by ethanol extraction exhibited broad antimicrobial activities. The antifungal compound is stable at 4-70 °C and pH 2.0-12.0. After treatment with proteinase K, the antifungal activity was not detected, indicating that the antifungal compound of strain YR247 is a peptidic compound. Electrospray ionization mass spectrometry of the purified antifungal compound indicated that the peptidic compound has an average molecular weight of 1167.9. The molecular weight of the antifungal compound from strain YR247 is different from those of antimicrobial peptides produced by the related Aneurinibacillus and Bacillus bacteria. The antifungal peptidic compound from the deep-sea bacterium Aneurinibacillus sp. YR247 may be useful as a biocontrol agent.

Aerial Warfare: A Volatile Dialogue between the Plant Pathogen Verticillium longisporum and Its Antagonist Paenibacillus polymyxa

Verticillium wilt caused by Verticillium spp. results in severe yield losses in a broad range of crops. Verticillium outbreaks are challenging to control, and exacerbated by increases in soil temperatures and drought associated with global warming. Employing natural antagonists as biocontrol agents offers a promising approach to addressing this challenge. Paenibacillus polymyxa Sb3-1 was proven to reduce the growth of Verticillium longisporum during in vitro experiments and was shown to promote the growth of oilseed rape seedlings infested with V. longisporum. Our novel approach combined in vitro and in planta methods with the study of the mode of interaction between Sb3-1 and V. longisporum EVL43 via their volatile organic compounds (VOCs). Volatile and soluble substances, produced by both microorganisms as a reaction to one another's VOCs, were detected by using both gas and liquid chromatography-mass spectrometry. P. polymyxa Sb3-1 continually produced antimicrobial and plant growth promoting VOCs, such as 2-nonanone and 3-hydroxy-2-butanone. Several other antimicrobial volatile substances, such as isoamyl acetate and durenol, were downregulated. The general metabolic activity of Sb3-1, including protein and DNA biotransformations, was upregulated upon contact with EVL43 VOCs. V. longisporum increased its production of antimicrobial substances, such as 1-butanol, and downregulated its metabolic activities upon exposure to Sb3-1 VOCs. Additionally, several stress response substances such as arabitol and protein breakdown products (e.g., L-Isoleucyl-L-glutamic acid), were increased in the co-incubated samples. The results obtained depict an ongoing dialog between these microorganisms resulting in growth inhibition, the slowing down of metabolism, and the cell death of V. longisporum due to contact with the P. polymyxa Sb3-1 VOCs. Moreover, the results indicate that VOCs make a substantial contribution to the interaction between pathogens and their natural antagonists and have the potential to control pathogens in a novel, environmentally friendly manner.

Use of the Endophytic Fungus Daldinia cf. concentrica and Its Volatiles as Bio-Control Agents

Endophytic fungi are organisms that spend most of their life cycle within plant tissues without causing any visible damage to the host plant. Many endophytes were found to secrete specialized metabolites and/or emit volatile organic compounds (VOCs), which may be biologically active and assist fungal survival inside the plant as well as benefit their hosts. We report on the isolation and characterization of a VOCs-emitting endophytic fungus, isolated from an olive tree (Olea europaea L.) growing in Israel; the isolate was identified as Daldinia cf. concentrica. We found that the emitted VOCs were active against various fungi from diverse phyla. Results from postharvest experiments demonstrated that D. cf. concentrica prevented development of molds on organic dried fruits, and eliminated Aspergillus niger infection in peanuts. Gas chromatography-mass spectrometry analysis of the volatiles led to identification of 27 VOCs. On the basis of these VOCs we prepared two mixtures that displayed a broad spectrum of antifungal activity. In postharvest experiments these mixtures prevented development of molds on wheat grains, and fully eliminated A. niger infection in peanuts. In light of these findings, we suggest use of D. cf. concentrica and/or its volatiles as an alternative approach to controlling phytopathogenic fungi in the food industry and in agriculture.