Identification of phenolics for control of Aspergillus flavus using Saccharomyces cerevisiae in a model target-gene bioassay

Carboxylic acid derivatives suppress the growth of Aspergillus flavus through the inhibition of fungal alpha-amylase

Aspergillus favus (A. flavus) is a saprophytic fungus and a pathogen affecting several important foods and crops, including maize. A. flavus produces a toxic secondary metabolite called aflatoxin. Alpha-amylase (α-amylase), a hydrolytic enzyme produced by A. Flavus helps in the production of aflatoxin by hydrolysing the starch molecules in to simple sugars such as glucose and maltose. These simple sugars induce the production of aflatoxin. Inhibition of α-amylase has been proven as a potential way to reduce the production of aflatoxin. In the present study, we investigated the effect of selected carboxylic acid derivatives such as cinnamic acid (CA), 2, 4-dichlorophenoxyacetic acid (2,4-D), and 3-(4-hydroxyphenyl)-propionic acid (3,4-HPPA) on the fungal growth and for the α-amylase inhibitory activity. The binding potentials of these compounds with α-amylase have been confirmed by enzyme kinetics and isothermal titration calorimetry. Molecular docking and MD simulation studies were also performed to deduce the atomic level interaction between the protein and selected ligands. The results indicated that CA, 2,4-D and 3,4-HPPA can inhibit the fungal growth which could be partly due to the inhibition on fungal α-amylase activity.Communicated by Ramaswamy H. Sarma.

Integrated analysis of transcriptome, metabolome, and histochemistry reveals the response mechanisms of different ages Panax notoginseng to root-knot nematode infection

Panax notoginseng (P. notoginseng) is an invaluable perennial medicinal herb. However, the roots of P. notoginseng are frequently subjected to severe damage caused by root-knot nematode (RKN) infestation. Although we have observed that P. notoginseng possessed adult-plant resistance (APR) against RKN disease, the defense response mechanisms against RKN disease in different age groups of P. notoginseng remain unexplored. We aimed to elucidate the response mechanisms of P. notoginseng at different stages of development to RKN infection by employing transcriptome, metabolome, and histochemistry analyses. Our findings indicated that distinct age groups of P. notoginseng may activate the phenylpropanoid and flavonoid biosynthesis pathways in varying ways, leading to the synthesis of phenolics, flavonoids, lignin, and anthocyanin pigments as both the response and defense mechanism against RKN attacks. Specifically, one-year-old P. notoginseng exhibited resistance to RKN through the upregulation of 5-O-p-coumaroylquinic acid and key genes involved in monolignol biosynthesis, such as PAL, CCR, CYP73A, CYP98A, POD, and CAD. Moreover, two-year-old P. notoginseng enhanced the resistance by depleting chlorogenic acid and downregulating most genes associated with monolignol biosynthesis, while concurrently increasing cyanidin and ANR in flavonoid biosynthesis. Three-year-old P. notoginseng reinforced its resistance by significantly increasing five phenolic acids related to monolignol biosynthesis, namely p-coumaric acid, chlorogenic acid, 1-O-sinapoyl-D-glucose, coniferyl alcohol, and ferulic acid. Notably, P. notoginseng can establish a lignin barrier that restricted RKN to the infection site. In summary, P. notoginseng exhibited a potential ability to impede the further propagation of RKN through the accumulation or depletion of the compounds relevant to resistance within the phenylpropanoid and flavonoid pathways, as well as the induction of lignification in tissue cells.

Finding a Novel Chalcone-Cinnamic Acid Chimeric Compound with Antiproliferative Activity against MCF-7 Cell Line Using a Free-Wilson Type Approach

In this work, we carried out the design and synthesis of new chimeric compounds from the natural cytotoxic chalcone 2',4'-dihydroxychalcone (2',4'-DHC, A) in combination with cinnamic acids. For this purpose, a descriptive and predictive quantitative structure-activity relationship (QSAR) model was developed to study the chimeric compounds' anti-cancer activities against human breast cancer MCF-7, relying on the presence or absence of structural motifs in the chalcone structure, like in a Free-Wilson approach. For this, we used 207 chalcone derivatives with a great variety of structural modifications over the α and β rings, such as halogens (F, Cl, and Br), heterocyclic rings (piperazine, piperidine, pyridine, etc.), and hydroxyl and methoxy groups. The multilinear equation was obtained by the genetic algorithm technique, using logIC₅₀ as a dependent variable and molecular descriptors (constitutional, topological, functional group count, atom-centered fragments, and molecular properties) as independent variables, with acceptable statistical parameter values (R2 = 86.93, Q2_LMO = 82.578, Q2_BOOT = 80.436, and Q2_EXT = 80.226), which supports the predictive ability of the model. Considering the aromatic and planar nature of the chalcone and cinnamic acid cores, a structural-specific QSAR model was developed by incorporating geometrical descriptors into the previous general QSAR model, again, with acceptable parameters (R2 = 85.554, Q2_LMO = 80.534, Q2_BOOT = 78.186, and Q2_EXT = 79.41). Employing this new QSAR model over the natural parent chalcone 2',4'-DHC (A) and the chimeric compound 2'-hydroxy,4'-cinnamate chalcone (B), the predicted cytotoxic activity was achieved with values of 55.95 and 17.86 µM, respectively. Therefore, to corroborate the predicted cytotoxic activity compounds A and B were synthesized by two- and three-step reactions. The structures were confirmed by ¹H and ¹³C NMR and ESI+MS analysis and further evaluated in vitro against HepG2, Hep3B (liver), A-549 (lung), MCF-7 (breast), and CasKi (cervical) human cancer cell lines. The results showed IC₅₀ values of 11.89, 10.27, 56.75, 14.86, and 29.72 µM, respectively, for the chimeric cinnamate chalcone B. Finally, we employed B as a molecular scaffold for the generation of cinnamate candidates (C-K), which incorporated structural motifs that enhance the cytotoxic activity (pyridine ring, halogens, and methoxy groups) according to our QSAR model. ADME/tox in silico analysis showed that the synthesized compounds A and B, as well as the proposed chalcones C and G, are the best candidates with adequate drug-likeness properties. From all these results, we propose B (as a molecular scaffold) and our two QSAR models as reliable tools for the generation of anti-cancer compounds over the MCF-7 cell line.

Synthetic Cinnamides and Cinnamates: Antimicrobial Activity, Mechanism of Action, and In Silico Study

The severity of infectious diseases associated with the resistance of microorganisms to drugs highlights the importance of investigating bioactive compounds with antimicrobial potential. Therefore, nineteen synthetic cinnamides and cinnamates having a cinnamoyl nucleus were prepared and submitted for the evaluation of antimicrobial activity against pathogenic fungi and bacteria in this study. To determine the minimum inhibitory concentration (MIC) of the compounds, possible mechanisms of antifungal action, and synergistic effects, microdilution testing in broth was used. The structures of the synthesized products were characterized with FTIR spectroscopy, ¹ H-NMR, ¹³ C-NMR, and HRMS. Derivative 6 presented the best antifungal profile, suggesting that the presence of the butyl substituent potentiates its biological response (MIC = 626.62 μM), followed by compound 4 (672.83 μM) and compound 3 (726.36 μM). All three compounds were fungicidal, with MFC/MIC ≤ 4. For mechanism of action, compounds 4 and 6 directly interacted with the ergosterol present in the fungal plasmatic membrane and with the cell wall. Compound 18 presented the best antibacterial profile (MIC = 458.15 μM), followed by compound 9 (550.96 μM) and compound 6 (626.62 μM), which suggested that the presence of an isopropyl group is important for antibacterial activity. The compounds were bactericidal, with MBC/MIC ≤ 4. Association tests were performed using the Checkerboard method to evaluate potential synergistic effects with nystatin (fungi) and amoxicillin (bacteria). Derivatives 6 and 18 presented additive effects. Molecular docking simulations suggested that the most likely targets of compound 6 in C. albicans were caHOS2 and caRPD3, while the most likely target of compound 18 in S. aureus was saFABH. Our results suggest that these compounds could be used as prototypes to obtain new antimicrobial drugs.

Screening, synthesis optimization, and scaling-up of phytopathogen antifungals derived from natural hydroxycinnamic acids

A simple screening methodology was employed to correlate the structures of hydroxycinnamic acids (HCAs) and their esterified derivatives with their in vitro antifungal activity over Fusarium oxysporum f. sp. lycopersici. The antifungal activity of the tested HCAs, i.e., coumaric > ferulic > sinapinic > caffeic acid, was higher after esterification and when the coumaric acid hydroxyl group was at the ortho-position. This outcome was strengthened by the elongation of the alkyl chain to 4-carbons and, particularly, by the esterification with isobutyl alcohol. The highest antifungal activity was obtained from isobutyl o-coumarate (iBoC), which inhibits 70% of mycelial growth at 1.2 mM. Thereby, a heterogeneous catalysis strategy was optimized by using the response surface methodology. At the best conditions found, the synthesis of iBoC was scaled up to 15 g, achieving 96% conversion yield in 48 h in a stirred batch reactor. This study reveals for the first time the potential of iBoC to provide commercial materials as antifungal agents to control F. oxysporum and other phytopathogenic fungi.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03425-7.

Peanut Seed Coat Acts as a Physical and Biochemical Barrier against Aspergillus flavus Infection

Aflatoxin contamination is a global menace that adversely affects food crops and human health. Peanut seed coat is the outer layer protecting the cotyledon both at pre- and post-harvest stages from biotic and abiotic stresses. The aim of the present study is to investigate the role of seed coat against A. flavus infection. In-vitro seed colonization (IVSC) with and without seed coat showed that the seed coat acts as a physical barrier, and the developmental series of peanut seed coat showed the formation of a robust multilayered protective seed coat. Radial growth bioassay revealed that both insoluble and soluble seed coat extracts from 55-437 line (resistant) showed higher A. flavus inhibition compared to TMV-2 line (susceptible). Further analysis of seed coat biochemicals showed that hydroxycinnamic and hydroxybenzoic acid derivatives are the predominant phenolic compounds, and addition of these compounds to the media inhibited A. flavus growth. Gene expression analysis showed that genes involved in lignin monomer, proanthocyanidin, and flavonoid biosynthesis are highly abundant in 55-437 compared to TMV-2 seed coats. Overall, the present study showed that the seed coat acts as a physical and biochemical barrier against A. flavus infection and its potential use in mitigating the aflatoxin contamination.

Repellency of Veratraldehyde (3,4-Dimethoxy Benzaldehyde) against Mosquito Females and Tick Nymphs

Arthropod-borne infectious diseases cause many deaths and a major economic burden worldwide. Repellents play an important role in protecting people from infectious biting arthropods. The repellency of veratraldehyde, a known food additive, and the WJ-1041 formulation containing 10% veratraldehyde was tested against Aedes albopictus and Culex pipiens pallens females and Haemaphysalis longicornis nymphs using arm-in-cage, indoor or filter paper tests. Veratraldehyde exhibited repellency similar to or lower than that of n,n-diethyl-meta-toluamide (DEET) against A. albopictus, but in H. longicornis, the activity of veratraldehyde was better than that of DEET. The repellency of the 10% veratraldehyde solution was comparable to that of 20% DEET against the two mosquitoes. When comparing repellency between the WJ-1041 formulation (10% veratraldehyde) and 10% DEET against C. pipiens pallens, A. Albopictus and H. longicornis, the two showed similar repellency and complete protection time (CPT) values. However, there was a small difference depending on the tested insects. The absorption of veratraldehyde via skin was minimal, if at all. The pharmacokinetic parameters (Cmax and Tmax) of veratraldehyde in blood samples of rats were not different from those of the control group. Based on these results, veratraldehyde has high potential to be commercialized as a repellent agent against infectious disease-borne pests in the near future.

Interactions between zinc and Phomopsis longicolla infection in roots of Glycine max

Phomopsis. longicolla is a hemibiotrophic fungus causing significant soybean yield loss worldwide. To reveal the role of zinc in plant-pathogen interactions, soybean seedlings were grown hydroponically with a range of Zn concentrations, 0.06 µM (deficient, Zn0), 0.4 µM (optimal growth), 1.5 µM, 4 µM, 12 µM, and toxic 38 μM, and were subsequently inoculated with P. longicolla via the roots. In vivo analysis of metal distribution in tissues by micro-X-ray fluorescence showed local Zn mobilization in the root maturation zone in all treatments. Decreased root and pod biomass, and photosynthetic performance in infected plants treated with 0.4 µM Zn were accompanied with accumulation of Zn, jasmonoyl-L-isoleucine (JA-Ile), jasmonic acid, and cell wall-bound syringic acid (cwSyA) in roots. Zn concentration in roots of infected plants treated with 1.5 µM Zn was seven-fold higher than in the 0.4 µM Zn treatment, which together with accumulation of JA-Ile, cwSyA, cell wall-bound vanilic acid and leaf jasmonates contributed to maintaining photosynthesis and pod biomass. Host-pathogen nutrient competition and phenolics accumulation limited the infection in Zn-deficient plants. The low infection rate in Zn 4 µM-treated roots correlated with salicylic and 4-hydroxybenzoic acid, and cell wall-bound p-coumaric acid accumulation. Zn toxicity promoted pathogen invasion and depleted cell wall-bound phenolics. The results show that manipulation of Zn availability improves soybean resistance to P. longicolla by stimulating phenolics biosynthesis and stress-inducible phytohormones.

Phenolic Acids Released in Maize Rhizosphere During Maize-Soybean Intercropping Inhibit Phytophthora Blight of Soybean

Interspecies interactions play a key role in soil-borne disease suppression in intercropping systems. However, there are limited data on the underlying mechanisms of soil-borne Phytophthora disease suppression. Here, a field experiment confirmed the effects of maize and soybean intercropping on Phytophthora blight of soybean caused by Phytophthora sojae. Experimentally, the roots and root exudates of maize were found to attract P. sojae zoospores and inhibit their motility and the germination of cystospores. Furthermore, five phenolic acids (p-coumaric acid, cinnamic acid, p-hydroxybenzoic acid, vanillic acid, and ferulic acid) that were consistently identified in the root exudates and rhizosphere soil of maize were found to interfere with the infection behavior of P. sojae. Among them, cinnamic acid was associated with significant chemotaxis in zoospores, and p-coumaric acid and cinnamic acid showed strong antimicrobial activity against P. sojae. However, in the rhizosphere soil of soybean, only p-hydroxybenzoic acid, low concentrations of vanillic acid, and ferulic acid were identified. Importantly, the coexistence of five phenolic acids in the maize rhizosphere compared with three phenolic acids in the soybean rhizosphere showed strong synergistic antimicrobial activity against the infection behavior of P. sojae. In summary, the types and concentrations of phenolic acids in maize and soybean rhizosphere soils were found to be crucial factors for Phytophthora disease suppression in this intercropping system.

Removal Ability and Resistance to Cinnamic and Vanillic Acids by Fungi

Twelve fungal strains were assayed to investigate their resistance to cinnamic and vanillic acids and their ability to remove these compounds from a liquid medium. In a first step, the effect of the two aromatic acids (1 g/L) on the fungal growth kinetic was studied. The results were modelled through a logistic like function (Dantigny equation) to estimate τ, which is the time to the half-maximum colony diameter. The key findings of this part were as follows: (i) generally, cinnamic acid exerted a stronger effect than vanillic acid; (ii) aromatic acids exerted a delay on the growth of some fungi and only one strain (Athelia rolfsii) was completely inhibited. In the second part, fungi were assayed to investigate their ability to remove cinnamic and vanillic acids (ca. 350 mg/kg) from liquid media at pH 3.5. The results indicated that the most efficient fungi were Aspergillus niger and Lasiodiplodia theobromae.

Cinnamaldehyde, a Promising Natural Preservative Against Aspergillus flavus

The problem of food spoilage due to Aspergillus flavus (A. flavus) needs to be resolved. In this study, we found that the minimum inhibitory concentration of cinnamaldehyde (CA) that inhibited A. flavus was 0.065 mg/ml and that corn can be prevented from spoiling at a concentration of 0.13 mg/cm3. In addition to inhibiting spore germination, mycelial growth, and biomass production, CA can also reduce ergosterol synthesis and can cause cytomembrane damage. Our intention was to elucidate the antifungal mechanism of CA. Flow cytometry, fluorescence microscopy, and western blot were used to reveal that different concentrations of CA can cause a series of apoptotic events in A. flavus, including elevated Ca2+ and reactive oxygen species, decrease in mitochondrial membrane potential (Δψ m ), the release of cytochrome c, the activation of metacaspase, phosphatidylserine (PS) externalization, and DNA damage. Moreover, CA significantly increased the expression levels of apoptosis-related genes (Mst3, Stm1, AMID, Yca1, DAP3, and HtrA2). In summary, our results indicate that CA is a promising antifungal agent for use in food preservation.

Improvement of taste and shelf life of yeasted low-salt bread containing functional sourdoughs using Lactobacillus amylovorus DSM 19280 and Weisella cibaria MG1

The challenge remains for the baking industry to reduce salt levels in yeasted bread as directed by governments, retailers and consumers around the world. The two main problems associated with the reduction of salt are a lack of salty taste and the reduction in shelf-life. Both of these issues are addressed in the presented work. A range of breads containing different levels of salt (0.0%, 0.3% and 1.2% of NaCl) in combination with various levels of sourdough (0%, 6%, 12%, 18%, 24%) was produced. The different doughs were analysed for their rheological behaviour. The bread quality characteristics such as loaf volume, crumb structure, staling rate and microbial shelf life were also determined. The sourdoughs were analysed for their different metabolites: organic acids, sugars, exopolysaccharides (EPS), and antifungal compounds. A trained sensory panel was used to perform descriptive analysis of the bread samples. The object of this paper is to use functional sourdoughs, containing Lactobacillus amylovorus DSM 19280 and Weisella cibaria MG1 to compensate for the quality problems that occur when salt is reduced in yeasted bread. The application of functional sourdoughs containing exopolysaccharides and/or antifungal substances in salt reduced breads significantly improved the quality. The application of functional sourdoughs allows the reduction of salt to a level of 0.3%.

The Antimicrobial Activity of Annona emarginata (Schltdl.) H. Rainer and Most Active Isolated Compounds against Clinically Important Bacteria

Annona emarginata (Schltdl.) H. Rainer, commonly known as “arachichú”, “araticú”, “aratigú”, and “yerba mora”, is a plant that grows in Argentina. Infusions and decoctions are used in folk medicine as a gargle against throat pain and for calming toothache; another way to use the plant for these purposes is chewing its leaves. Extracts from bark, flowers, leaves, and fruits from A. emarginata were subjected to antibacterial assays against a panel of Gram (+) and Gram (−) pathogenic bacteria according to Clinical and Laboratory Standards Institute protocols. Extracts from the stem bark and leaves showed moderate activity against the bacteria tested with values between 250–1000 µg/mL. Regarding flower extracts, less polar extracts (hexane, dichloromethane) showed very strong antibacterial activity against methicillin-sensitive Staphylococcus aureus ATCC 25923 and methicillin-resistant S. aureus ATCC 43300 with values between 16–125 µg/mL. Additionally, hexane extract showed activity against Klebsiella pneumoniae (MIC = 250 µg/mL). The global methanolic extract of the fruits (MeOHGEF) was also active against the three strains mentioned above, with MICs values 250–500 µg/mL. Bioassay-guided fractionation of MeOHGEF led to the isolation of a new main compound—(R)-2-(4-methylcyclohex-3-en-1-yl)propan-2-yl (E)-3-(4-hydroxyphenyl)acrylate (1). The structure and relative configurations have been determined by means of 1D and 2D NMR techniques, including COSY, HMQC, HMBC, and NOESY correlations. Compound 1 showed strong antimicrobial activity against all Gram (+) species tested (MICs = 3.12–6.25 µg/mL). In addition, the synthesis and antibacterial activity of some compounds structurally related to compound 1 (including four new compounds) are reported. A SAR study for these compounds was performed based on the results obtained by using molecular calculations.

Design, Synthesis and Biological Evaluation of Novel Primaquine-Cinnamic Acid Conjugates of the Amide and Acylsemicarbazide Type

In this paper design and synthesis of a scaffold comprising primaquine (PQ) motif and cinnamic acid derivatives (CADs) bound directly (compounds 3a-k) or via a spacer (compounds 7a-k) are reported. In the first series of compounds, PQ and various CADs were connected by amide bonds and in the second series by acylsemicarbazide functional groups built from the PQ amino group, CONHNH spacer and the carbonyl group originating from the CADs. PQ-CAD amides 3a-k were prepared by a simple one-step condensation reaction of PQ with a series of CAD chlorides (method A) or benzotriazolides 2 (method B). The synthesis of acylsemicarbazides 7a-k included activation of PQ with benzotriazole, preparation of PQ-semicarbazide 6 and its condensation with CAD chlorides 4. All synthesized PQ-CAD conjugates were evaluated for their anticancer, antiviral and antioxidative activities. Almost all compounds from series 3 were selective towards the MCF-7 cell line and active at micromolar concentrations. The o-fluoro derivative 3h showed high activity against HeLa, MCF-7 and in particular against the SW 620 cell line, while acylsemicarbazide 7f with a benzodioxole ring and 7c, 7g and especially 7j with methoxy-, chloro- or trifluoromethyl-substituents in the para position showed high selectivity and high inhibitory activity against MCF-7 cell line at micromolar (7c, 7f, 7g) and nanomolar (7j) levels. Acylsemicarbazide derivatives with trifluoromethyl group(s) 7i, 7j and 7k showed specific activity against human coronavirus (229E) at concentrations which did not alter the normal cell morphology. The same compounds exerted the most potent reducing activity in the DPPH test, together with 7d and 7g, while methoxy (compounds 7c-e), benzodioxole (7f), p-Cl (7g) and m-CF₃ (7i) acylsemicarbazides and amide 3f presented the highest LP inhibition (83%-89%). The dimethoxy derivative 7d was the most potent LOX inhibitor (IC50 = 10 μΜ). The performed biological tests gave evidence of acylsemicarbazide functional group as superior binding group in PQ-CAD conjugates.

Simultaneous decontamination and drying of rough rice using combined pulsed light and holding treatment

BACKGROUND

Pulsed light (PL) technology has been proven effective in food disinfection. However, increasing the light intensity or treatment time could swiftly increase the temperature of the food product. Using the thermal effect in an appropriate way may achieve a simultaneous disinfection and drying effect. The objective of this study was to investigate the feasibility of simultaneous disinfection and drying of rough rice using PL and holding treatment.

RESULTS

Freshly harvested rice samples were inoculated by Aspergillus flavus (A. flavus) and treated using PL under different intensities and durations followed by holding treatment. The PL treatment under intensity of 1.08 W cm(-2) for 21 s led to a reduction of 0.29 log cfu g(-1) on the population size of A. flavus spores. After holding treatment, a 5.2 log cfu g(-1) reduction was achieved. The corresponding total moisture removal reached 3.3% points. No adverse effect on milling quality was detected after the treatment.

CONCLUSION

The obtained results revealed that the combined PL and holding treatment had good potential for successful application in the rice industry to simultaneously achieve disinfection and drying. © 2015 Society of Chemical Industry.

Maize-Pathogen Interactions: An Ongoing Combat from a Proteomics Perspective

Maize (Zea mays L.) is a host to numerous pathogenic species that impose serious diseases to its ear and foliage, negatively affecting the yield and the quality of the maize crop. A considerable amount of research has been carried out to elucidate mechanisms of maize-pathogen interactions with a major goal to identify defense-associated proteins. In this review, we summarize interactions of maize with its agriculturally important pathogens that were assessed at the proteome level. Employing differential analyses, such as the comparison of pathogen-resistant and susceptible maize varieties, as well as changes in maize proteomes after pathogen challenge, numerous proteins were identified as possible candidates in maize resistance. We describe findings of various research groups that used mainly mass spectrometry-based, high through-put proteomic tools to investigate maize interactions with fungal pathogens Aspergillus flavus, Fusarium spp., and Curvularia lunata, and viral agents Rice Black-streaked Dwarf Virus and Sugarcane Mosaic Virus.

Inhibition of ochratoxin A production in Aspergillus carbonarius by hydroxycinnamic acids from grapes

Hydroxycinnamic acids (HCAs), phenolic components of wine, are known to have antimicrobial properties. Aspergillus carbonarius is one of the most important ochratoxin A (OTA) producing fungi in wine. Strategies for the control and prevention of A. carbonarius contamination are important for the maintenance of wine safety. This study sought to determine the potential of HCAs, such as caffeic, p-coumaric and ferulic acids, as antifungal natural compounds for the control of A. carbonarius growth and OTA production. The HCAs were tested at the increasing concentrations of 0.30, 0.65 and 1.10 mg/ml in minimal medium (MM) and grape juice. Germination of conidia was not affected in neither of the two media in presence of HCAs. At all the concentrations tested, OTA biosynthesis in MM was reduced and the dose effect was more evident for p-coumaric and ferulic acids; in grape juice the reduction trend was confirmed, and ferulic acid showed the highest inhibitory effect. Moreover, the expression level of genes encoding a polyketide synthase (AcOTApks) and a nonribosomal peptide synthetase (AcOTAnrps) involved in OTA biosynthesis, was evaluated by real-time PCR in A. carbonarius grown in presence of 0.65 mg/ml of HCAs. From gene expression analysis only the AcOTApks gene showed a marked reduction of transcription level in presence of p-coumaric and ferulic acids. On the contrary, caffeic acid seemed to not influence the expression levels of the genes analysed in this study, suggesting a different mechanism of action on the regulation of OTA biosynthesis.

Effective disinfection of rough rice using infrared radiation heating

The objective of this study was to investigate the effect of infrared (IR) heating and tempering treatments on disinfection of Aspergillus flavus in freshly harvested rough rice and storage rice. Rice samples with initial moisture contents (IMCs) of 14.1 to 27.0% (wet basis) were infected with A. flavus spores before the tests. The infected samples were heated by IR radiation to 60°C in less than 1 min, and then samples were tempered at 60°C for 5, 10, 20, 30, 60, or 120 min. High heating rates and corresponding high levels of moisture removal were achieved using IR heating. The highest total moisture removal was 5.3% for the fresh rice with an IMC of 27.0% after IR heating and then 120 min of tempering. IR heating followed by tempering for 120 min resulted in 2.5- and 8.3-log reductions of A. flavus spores in rough rice with the lowest and highest IMCs, respectively. To study the effect on disinfection of rewetting dried storage rice, the surface of the dry rice was rewetted to achieve IMCs of 14.7 to 19.4% (wet basis). The rewetting process for the dry rice had a significant effect on disinfection. IR heating followed by tempering for 60 min resulted in 7.2-log reductions in A. flavus on rewetted rough rice. The log-linear plus tail model was applied to estimate the tempering time needed to achieve a 5-log reduction of A. flavus in rice of different IMCs. At least 30 and 20 min of tempering were needed for fresh rice and rewetted rice, respectively, with the highest IMCs. The recommended conditions of simultaneous disinfection and drying for fresh rice was IR heating to 60°C followed by tempering for 120 min and natural cooling, resulting in a final MC of 16.5 to 22.0%, depending on the IMC. For the rewetted dry rice with an IMC of 19.4%, the recommended condition for disinfection and drying involved only 20 min of tempering. The final MC of the sample was 13.8%, which is a safe MC for storage rice.

Natural and natural-like phenolic inhibitors of type B trichothecene in vitro production by the wheat (Triticum sp.) pathogen Fusarium culmorum

Fusarium culmorum, a fungal pathogen of small grain cereals, produces 4-deoxynivalenol and its acetylated derivatives that may cause toxicoses on humans or animals consuming contaminated food or feed. Natural and natural-like compounds belonging to phenol and hydroxylated biphenyl structural classes were tested in vitro to determine their activity on vegetative growth and trichothecene biosynthesis by F. culmorum. Most of the compounds tested at 1.5 or 1.0 mM reduced 3-acetyl-4-deoxynivalenol production by over 70% compared to the control, without affecting fungal growth significantly. Furthermore, several compounds retained their ability to inhibit toxin in vitro production at the lowest concentrations of 0.5 and 0.25 mM. Magnolol 27 showed fungicidal activity even at 0.1 mM. No linear correlation was observed between antioxidant properties of the compounds and their ability to inhibit fungal growth and mycotoxigenic capacity. A guaiacyl unit in the structure may play a key role in trichothecene inhibition.

Antifungal activity of cinnamic acid derivatives involves inhibition of benzoate 4-hydroxylase (CYP53)

AIMS

CYP53A15, from the sorghum pathogen Cochliobolus lunatus, is involved in detoxification of benzoate, a key intermediate in aromatic compound metabolism in fungi. Because this enzyme is unique to fungi, it is a promising drug target in fungal pathogens of other eukaryotes.

METHODS AND RESULTS

In our work, we showed high antifungal activity of seven cinnamic acid derivatives against C. lunatus and two other fungi, Aspergillus niger and Pleurotus ostreatus. To elucidate the mechanism of action of cinnamic acid derivatives with the most potent antifungal properties, we studied the interactions between these compounds and the active site of C. lunatus cytochrome P450, CYP53A15.

CONCLUSION

We demonstrated that cinnamic acid and at least four of the 42 tested derivatives inhibit CYP53A15 enzymatic activity.

SIGNIFICANCE AND IMPACT OF THE STUDY

By identifying selected derivatives of cinnamic acid as possible antifungal drugs, and CYP53 family enzymes as their targets, we revealed a potential inhibitor-target system for antifungal drug development.

Differential adaptation to multi-stressed conditions of wine fermentation revealed by variations in yeast regulatory networks

BACKGROUND

Variation of gene expression can lead to phenotypic variation and have therefore been assumed to contribute the diversity of wine yeast (Saccharomyces cerevisiae) properties. However, the molecular bases of this variation of gene expression are unknown. We addressed these questions by carrying out an integrated genetical-genomic study in fermentation conditions. We report here quantitative trait loci (QTL) mapping based on expression profiling in a segregating population generated by a cross between a derivative of the popular wine strain EC1118 and the laboratory strain S288c.

RESULTS

Most of the fermentation traits studied appeared to be under multi-allelic control. We mapped five phenotypic QTLs and 1465 expression QTLs. Several expression QTLs overlapped in hotspots. Among the linkages unraveled here, several were associated with metabolic processes essential for wine fermentation such as glucose sensing or nitrogen and vitamin metabolism. Variations affecting the regulation of drug detoxification and export (TPO1, PDR12 or QDR2) were linked to variation in four genes encoding transcription factors (PDR8, WAR1, YRR1 and HAP1). We demonstrated that the allelic variation of WAR1 and TPO1 affected sorbic and octanoic acid resistance, respectively. Moreover, analysis of the transcription factors phylogeny suggests they evolved with a specific adaptation of the strains to wine fermentation conditions. Unexpectedly, we found that the variation of fermentation rates was associated with a partial disomy of chromosome 16. This disomy resulted from the well known 8-16 translocation.

CONCLUSIONS

This large data set made it possible to decipher the effects of genetic variation on gene expression during fermentation and certain wine fermentation properties. Our findings shed a new light on the adaptation mechanisms required by yeast to cope with the multiple stresses generated by wine fermentation. In this context, the detoxification and export systems appear to be of particular importance, probably due to nitrogen starvation. Furthermore, we show that the well characterized 8-16 translocation located in SSU1, which is associated with sulfite resistance, can lead to a partial chromosomic amplification in the progeny of strains that carry it, greatly improving fermentation kinetics. This amplification has been detected among other wine yeasts.

Gene targets for fungal and mycotoxin control

It was initially shown that gallic acid, from hydrolysable tannins in the pelliele of walnut kernels, dramatically inhibits biosynthesis of aflatoxin byAspergillus flavus. The mechanism of this inhibition was found to take place upstream from the gene cluster, including the regulatory gene,aflR, involved in aflatoxin biosynthesis. Additional research using other antioxidant phenolics showed similar antiaflatoxigenic activity to gallic acid. Treatment ofA. flavus withtert-butyl hydroperoxide resulted in an almost doubling of aflatoxin biosynthesis compared to untreated samples. Thus, antioxidative response systems are potentially useful molecular targets for control ofA. flavus. A high throughput screening system was developed using yeast,Saccharomyces cerevisiae, as a model fungus. This screening provided an avenue to quickly identify fungal genes that were vulnerable to treatment by phenolic compounds. The assay also provided a means to quickly assess effects of combinations of phenolics and certain fungicides affecting mitochondrial respiration. For example, theS. cerevisiae sod2† mutant was highly sensitive to treatment by certain phenolics and strobilurins/antimycin A, fungicides which inhibit complex III of the mitochondrial respiratory chain. Verification of stress to this system in the target fungus,A. flavus, was shown through complementation analysis, wherein the mitochondrial superoxide dismutase (Mn-SOD) gene (sodA) ofA. flavus in the ortholog mutant,sod2†, ofS. cerevisiae, relieved phenolic-induced stress. Mitochondrial antioxidative stress systems play an important role in fungal response to antifungals. Combined treatment of fungi with phenolics and inhibitors of mitochondrial respiration can effectively suppress growth ofA. flavus in a synergistic fashion.

Cinnamic Acid Derivatives Acting against Aspergillus Fungi.Taq Polymerase I a Potential Molecular Target

Some members of a series of cinnamic acid derivatives possess promising inhibitory activities in cellular assays against fungi of the Aspergillus genus. In order to search for a possible molecular target of such compounds, their role as Taq polymerase I inhibitors was studied. Four of the compounds studied displayed IC50 values within the range of those considered active as DNA polymerase inhibitors when searching for new cytotoxic molecules. The results obtained in our molecular modeling study appear to show that the inhibitory activity depends on the presence of a stabilizing interaction between the phenylpropanoid derivatives and the residues Asp610, Thr664, Phe667, Tyr671, and Asp785 located in the active site of Taq polymerase I. Also, it is possible to assert that the polymerization of DNA would be the molecular target of cinnamic acid derivatives with antifungal activity, which correlates with the inhibition of Taq polymerase I and the quantitative descriptor for the lipophilia (ClogP).

Antimicrobial phenylpropanoids from the Argentinean highland plant Parastrephia lucida (Meyen) Cabrera

ETHNOPHARMACOLOGICAL RELEVANCE

The Argentinean highland plant Parastrephia lucida (Meyen) Cabrera is used in traditional medicine as an antiseptic and anti-inflammatory crude drug.

AIM OF THE STUDY

To relate the antimicrobial effect of the crude drug with the constituents of the active fractions and traditional use.

MATERIALS AND METHODS

Assay-guided isolation of the methanol (MeOH) plant extract was carried out using bacteria and yeasts as target organisms. Both ATCC and local strains were included in the study. The antimicrobial fractions and compounds were detected by bioautographic assays. Minimum inhibitory concentrations (MIC) of each extract and fraction were determined and compared with reference antibiotics. Fractions were analyzed by HPLC-DAD, GC-MS, (1)H NMR and (13)C NMR.

RESULTS

From the MeOH extract of the plant, assay-guided isolation of the antimicrobial constituents led to 12 phenylpropanoids and two simple phenolics. Most of the compounds occurring in the active fractions were E-caffeoyl or E-cinnamoyl esters including prenyl and phenethyl derivatives. The MIC values of the most active fractions ranged between 12.5 and 200 μg/mL against reference strains and local isolates of Staphylococcus aureus and Enterococcus faecalis.

CONCLUSIONS

The antimicrobial effect found in the crude drug was associated with mixtures of phenylpropanoids, including prenyl and phenethyl esters of caffeic and cinnamic acids. The results support at least in part the traditional use of the plant as local antiseptic.

(E)-Methyl 2-[(2-formyl-6-meth-oxy-phen-oxy)meth-yl]-3-phenyl-acrylate

The title compound, C(19)H(18)O(5), crystallizes with two independent mol-ecules (A and B) in an asymmetric unit in both of which the two aromatic rings are in a bis-ectional orientation as evidenced by the dihedral angle between them [41.7 (1)° in mol-ecule A and 35.6 (1)° in mol-ecule B]. Both mol-ecules adopt an E configuration with respect to the C=C bond. An intra-molecular C-H⋯O hydrogen-bond occurs in mol-ecule A. The crystal packing features inter-molecular C-H⋯O inter-actions.

The fungal pathogen Cochliobolus heterostrophus responds to maize phenolics: novel small molecule signals in a plant-fungal interaction

The transcription factor ChAP1 of the fungal pathogen of maize, Cochliobolus heterostrophus, responds to oxidative stress by migration to the nucleus and activation of antioxidant genes. Phenolic and related compounds found naturally in the host also trigger nuclear localization of ChAP1, but only slight upregulation of some antioxidant genes. ChAP1 thus senses phenolic compounds without triggering a strong antioxidant response. We therefore searched for genes whose expression is regulated by phenolic compounds and/or ChAP1. The C. heterostrophus genome contains a cluster of genes for metabolism of phenolics. One such gene, catechol dioxygenase CCHD1, was induced at least 10-fold by caffeic and coumaric acids. At high phenolic concentrations (≥ 1.6 mM), ChAP1 is needed for maximum CCHD1 expression. At micromolar levels of phenolics CCHD1 is as strongly induced in chap1 mutants as in the wild type. The pathogen thus detects phenolics by at least two signalling pathways: one causing nuclear retention of ChAP1, and another triggering induction of CCHD1 expression. The low concentrations required for induction of CCHD1 indicate fungal receptors for plant phenolics. Symbiotic and pathogenic bacteria are known to detect phenolics, and our findings generalize this to a eukaryotic pathogen. Phenolics and related compounds thus provide a ubiquitous plant-derived signal.

Proteomic analysis of the maize rachis: potential roles of constitutive and induced proteins in resistance to Aspergillus flavus infection and aflatoxin accumulation

Infection of the maize (Zea mays L.) with aflatoxigenic fungus Aspergillus flavus and consequent contamination with carcinogenic aflatoxin is a persistent and serious agricultural problem causing disease and significant crop losses worldwide. The rachis (cob) is an important structure of maize ear that delivers essential nutrients to the developing kernels and A. flavus spreads through the rachis to infect kernels within the ear. Therefore, rachis plays an important role in fungal proliferation and subsequent kernel contamination. We used proteomic approaches and investigated the rachis tissue from aflatoxin accumulation resistant (Mp313E and Mp420) and susceptible (B73 and SC212m) maize inbred lines. First, we compared rachis proteins from resistant and susceptible inbred lines, which revealed that the young resistant rachis contains higher levels of abiotic stress-related proteins and proteins from phenylpropanoid metabolism, whereas susceptible young rachis contains pathogenesis-related proteins, which are generally inducible upon biotic stress. Second, we identified A. flavus-responsive proteins in rachis of both resistant and susceptible genotypes after 10- and 35-day infection. Differential expression of many stress/defense proteins during rachis juvenility, maturation and after A. flavus challenge demonstrates that resistant rachis relies on constitutive defenses, while susceptible rachis is more dependent on inducible defenses.

Use of chemosensitization to overcome fludioxonil resistance in Penicillium expansum

AIM

To overcome fludioxonil resistance of Penicillium expansum, a mycotoxigenic fungal pathogen causing postharvest decay in apple, by using natural phenolic chemosensitizing agents.

METHODS AND RESULTS

Fludioxonil-resistant mutants of P. expansum were co-treated with different oxidising and natural phenolic agents. Resistance was overcome by natural phenolic chemosensitizing agents targeting the oxidative stress-response pathway. These agents also augmented effectiveness of the fungicide, kresoxim-methyl. Results indicated that alkyl gallates target mitochondrial respiration and/or its antioxidation system. Fungal mitochondrial superoxide dismutase (Mn-SOD) plays a protective role against alkyl gallates.

CONCLUSIONS

Natural chemosensitizing agents targeting the oxidative stress-response system, such as Mn-SOD, can synergize commercial fungicides.

SIGNIFICANCE AND IMPACT OF THE STUDY

Redox-active compounds can serve as potent chemosensitizing agents to overcome resistance and lower effective dosages of fungicides. This can reduce costs with coincidental lowering of environmental and health risks.

De novo biosynthesis of defense root exudates in response to Fusarium attack in barley

Summary *Despite recent advances in elucidation of natural products in root exudates, there are significant gaps in our understanding of the ecological significance of products in the rhizosphere. *Here, we investigated the potential of barley (Hordeum vulgare) to secrete defense root exudates when challenged by the soilborne pathogen Fusarium graminearum. *Liquid chromatography with photodiode array detection (LC-DAD) was used to profile induced small-molecular-weight exudates. Thus, t-cinnamic, p-coumaric, ferulic, syringic and vanillic acids were assigned to plant metabolism and were induced within 2 d after Fusarium inoculation. Biological tests demonstrated the ability of those induced root exudates to inhibit the germination of F. graminearum macroconidia. In vivo labeling experiments with (13)CO(2) revealed that the secreted t-cinnamic acid was synthesized de novo within 2 d of fungal infection. Simultaneously to its root exudation, t-cinnamic acid was accumulated in the roots. Microscopic analysis showed that nonlignin cell wall phenolics were induced not only in necrosed zones but in all root tissues. *Results suggest that barley plants under attack respond by de novo biosynthesis and secretion of compounds with antimicrobial functions that may mediate natural disease resistance.

Inhibitory effects of Ephedra major Host on Aspergillus parasiticus growth and aflatoxin production

This study was undertaken to evaluate the effect of Ephedra major Host, an important medicinal plant with various biological activities, on growth and aflatoxin (AF) production by Aspergillus parasiticus NRRL 2999. The fungus was cultured in yeast extract-sucrose (YES) broth, a conductive medium that supports AF production, in the presence of various concentrations of essential oil (EO), hexanic and methanolic extracts of plant aerial parts, fruits, and roots using microbioassay technique. After incubating for 96 h at 28 degrees C in static conditions, mycelial dry weight was determined as an index of fungal growth, and aflatoxin B(1) (AFB(1)) was measured using HPLC technique. Based on the obtained results, EO of plant aerial parts significantly inhibited fungal growth at the highest concentration of 1000 microg/ml without any obvious effect on AFB(1) production at all concentrations used. Among plant extracts tested, only methanolic extract of aerial parts and roots were found to inhibit fungal growth and AFB(1) production dose-dependently with an IC(50) value of 559.74 and 3.98 microg/ml for AFB(1), respectively. Based on the GC/MS data, the major components of E. major EO were bis (2-ethylhexyl) phthalate (42.48%), pentacosane (20.94%), docosane (14.64%), citronellol (5.15%), heptadecan (4.41%), cis-3-Hexen-1-ol benzoate (4.07%), and 7-Octen-2-ol (3.25%). With respect to the potent inhibition of fungal growth and AF production by E. major, this plant may be useful in protecting crops from both toxigenic fungal growth and AF contamination.

CYP53A15 of Cochliobolus lunatus, a target for natural antifungal compounds

A novel cytochrome P450, CYP53A15, was identified in the pathogenic filamentous ascomycete Cochliobolus lunatus. The protein, classified into the CYP53 family, was capable of para hydroxylation of benzoate. Benzoate is a key intermediate in the metabolism of aromatic compounds in fungi and yet basically toxic to the organism. To guide functional analyses, protein structure was predicted by homology modeling. Since many naturally occurring antifungal phenolic compounds are structurally similar to CYP53A15 substrates, we tested their putative binding into the active site of CYP53A15. Some of these compounds inhibited CYP53A15. Increased antifungal activity was observed when tested in the presence of benzoate. Some results suggest that CYP53A15 O-demethylation activity is important in detoxification of other antifungal substances. With the design of potent inhibitors, CYP53 enzymes could serve as alternative antifungal drug targets.

Structure-antifungal activity relationship of cinnamic acid derivatives

A structure-antifungal activity relationship (SAR) study of 22 related cinnamic acid derivatives was carried out. Attention was focused on the antifungal activities exhibited against Aspergillus flavus, Aspergillus terreus, and Aspergillus niger. (E)-3-(4-methoxy-3-(3-methylbut-2-enyl)phenyl)acrylic acid (16) exhibited antifungal activity against A. niger, comparable to that of miconazole and a significant antifungal effect against A. flavus and A. terreus as well. A structure-activity relationship (SAR) study of related cinnamic acid derivatives has allowed a model to be proposed for the recognition of the minimal structural requirements for the antifungal effect in this series.

Biodiversity ofAspergillussectionFlaviin the United States: A review

Fungi belonging to Aspergillus section Flavi are of great economic importance in the United States due to their ability to produce toxic and carcinogenic aflatoxins in agricultural commodities. Development of control strategies against A. flavus and A. parasiticus, the major aflatoxin-producing species, is dependent upon a basic understanding of their diversity in agricultural ecosystems. This review summarizes our current knowledge of species and population diversity in the United States in relation to morphology, mycotoxin production and genetic characters. The high genetic diversity in populations of aflatoxigenic fungi is a reflection of their versatile habits in nature, which include saprotrophic colonization of plant debris in soil and parasitism of seeds and grain. Genetic variation within populations may originate from a cryptic sexual state. The advent of intensive monoculture agriculture not only increases population size but also may introduce positive selective pressure for aflatoxin production due to its link with pathogenicity in crops. Important goals in population research are to determine how section Flavi diversity in agricultural ecosystems is changing and to measure the direction of this evolution.

Targeting antioxidative signal transduction and stress response system: control of pathogenic Aspergillus with phenolics that inhibit mitochondrial function

AIMS

The aim of this study was to show whether antioxidative response systems are potentially useful molecular targets for control of Aspergillus fumigatus and Aspergillus flavus. Selected phenolic agents are used in target-gene-based bioassays to determine their impact on mitochondrial respiration.

METHODS AND RESULTS

Vanillyl acetone, vanillic acid, vanillin, cinnamic acid, veratraldehyde, m-coumaric acid (phenolic agents to which Saccharomyces cerevisiae sod2delta mutant showed sensitivity), carboxin (inhibits complex II of the mitochondrial respiratory chain), strobilurins/antimycin A (inhibits complex III of the mitochondrial respiratory chain) and fludioxonil/fenpiclonil [antifungals potentiated by mitogen-activated protein kinase (MAPK)] were examined in A. fumigatus, A. flavus and S. cerevisiae. Individual or combined application of phenolics with inhibitors of mitochondrial respiration showed some of the phenolics effectively inhibited fungal growth. Target-gene bioassays were performed using a sakAdelta (MAPK deletion) strain of A. fumigatus and a complementation analysis using the mitochondrial superoxide dismutase (Mn-SOD) gene (sodA) of A. flavus in the ortholog mutant, sod2delta, of S. cerevisiae. The results demonstrated that mitochondrial antioxidative stress system plays important roles in fungal response to antifungal agents tested.

CONCLUSIONS

Antioxidative response systems of fungi can be an efficient molecular target of phenolics for pathogen control. Combined application of phenolics with inhibitors of mitochondrial respiration can effectively suppress the growth of fungi.

SIGNIFICANCE AND IMPACT OF THE STUDY

Natural compounds that do not pose any significant medical or environmental risks could serve as useful alternatives or additives to conventional antifungals. Identifying the antioxidative response systems in other pathogens could improve methods for fungal control.

Controlling food-contaminating fungi by targeting their antioxidative stress-response system with natural phenolic compounds

The antioxidative stress-response system is essential to fungi for tolerating exposure to phenolic compounds. We show how this system can be targeted to improve fungal control by using compounds that inhibit the fungal mitochondrial respiratory chain. Targeting mitochondrial superoxide dismutase with selected phenolic acid derivatives (e.g., vanillyl acetone) resulted in a 100- to 1,000-fold greater sensitivity to strobilurin or carboxin fungicides. This synergism is significantly greater with strobilurin than with carboxin, suggesting that complex III of the mitochondrial respiratory chain is a better target than complex II for fungal control, using phenolics. These results show certain natural compounds are effective synergists to commercial fungicides and can be used for improving control of food-contaminating pathogens. These results suggest that the use of such compounds for fungal control can reduce environmental and health risks associated with commercial fungicides, lower cost for control, and the probability for development of resistance.