Control of postharvest fungal pathogens by antifungal compounds from Penicillium expansum

Pseudomonas synxantha volatile organic compounds: efficacy against Cadophora luteo-olivacea and Botrytis cinerea of kiwifruit

Volatile organic compounds (VOCs) are responsible for the antagonistic activity exerted by different biological control agents (BCAs). In this study, VOCs produced by Pseudomonas synxantha strain 117-2b were tested against two kiwifruit fungal postharvest pathogens: Cadophora luteo-olivacea and Botrytis cinerea, through in vitro and in vivo assays. In vitro results demonstrated that P. synxantha 117-2b VOCs inhibit mycelial growth of C. luteo-olivacea and B. cinerea by 56% and 42.8% after 14 and 5 days of exposition, respectively. In vivo assay demonstrated significant inhibitory effects. VOCs used as a biofumigant treatment reduced skin-pitting symptoms disease severity by 28.5% and gray mold incidence by 66.6%, with respect to the untreated control. BCA volatiles were analyzed by solid-phase microextraction coupled with gas chromatography-mass spectrometry (SPME-GC/MS), and among the detected compounds, 1-butanol, 3-methyl and 1-nonene resulted as the most produced. Their efficacy as pure synthetic compounds was assayed against mycelial growth of fungal pathogens by different concentrations (0.34, 0.56, and 1.12 µL mL-1 headspace). The effect of the application of VOCs as a biofumigant was also investigated as the expression level of seven defense-related genes of kiwifruit at different exposition times. The results indicated an enhancement of the expression of almost all the genes starting from 3 h of treatment. These results described P. synxantha VOCs characteristics and their potential as a promising method to adopt for protecting kiwifruit from postharvest diseases caused by C. luteo-olivacea and B. cinerea.

Identification of bioactive compounds of Bacillus velezensis HNA3 that contribute to its dual effects as plant growth promoter and biocontrol against post-harvested fungi

IMPORTANCE

The current study is an extension to our previous work on the plant growth-promoting rhizobacteria (PGPR) Bacillus velezensis HNA3 strain, which comes to confirm and reveals the huge stock of active secondary metabolites produced by HNA3. HNA3-emitted volatile organic compounds (VOCs) have demonstrated the capacity to impede the growth of phytopathogens affecting some fruits and vegetables, even in the absence of direct contact. Additionally, these volatiles enhanced soybean seed germination by breaking seed dormancy and inducing root system development. Furthermore, they promoted seedling growth, giving it prominence in soybean cultivation. The relevance of active volatiles derives from the fact that they can be developed as natural-safe biocontrol agents and plant promoters. This research validates the remarkable bioactivities exhibited by the Bacillus velezensis HNA3 and their potential applications in agriculture as an inoculant, encompassing biocontrol, plant growth promotion, and seed germination activities, thereby offering a safer alternative to hazardous chemicals.

Antifungal Activity of Volatile Components from Ceratocystis fimbriata and Its Potential Biocontrol Mechanism on Alternaria alternata in Postharvest Cherry Tomato Fruit

Infection by fungal pathogens is the main factor leading to postharvest rot and quality deterioration of fruit and vegetables. Rotting caused by Alternaria alternata is a concerning disease for numerous crops in both production and postharvest stages, especially tomato black spots. In this study, the double Petri dish assay showed that the VOCs of Ceratocystis fimbriata WJSK-1 and Mby inhibited the mycelial growth of fungal pathogen A. alternata, with a percentage inhibition of 52.2% and 42.9%. Then, HS-SPME-GC-MS technology was used to analyze the volatiles produced by two strains of C. fimbriata (WJSK-1, Mby), a total of 42 volatile single components were obtained, the main volatiles compounds identified include nine esters, 10 ketones, five alcohols, four aldehydes, three aromatic hydrocarbons, three heterocycles, four alkenes, three alkanes, and one acid. After that, the antifungal activity of a single volatile component was evaluated both in vitro and in vivo, four single components with antifungal effects were screened out, namely, benzaldehyde, nonanal, 2-Phenylethanol and isoamyl acetate, with IC₅₀ values show the smallest values for benzaldehyde and nonanal at 0.11 μL mL^-1, 0.04 μL mL^-1. A. alternata exposed to VOCs had abnormal morphology for hyphae, delayed sporulation, and inhibited spore germination. In vivo experiment shows that the four volatile components can effectively suppress disease incidence on fungal-inoculated fruit; the two aldehydes (benzaldehyde and nonanal) have more prominent effect on delaying fruit onset of disease. The results showed that VOCs produced by C. fimbriata have potential as a fumigant for controlling black rot in cherry tomatoes. IMPORTANCE In this research, the volatile organic compounds (VOCs) produced based on C. fimbriata exhibited strong antifungal activity against the fungal pathogen A. alternata. Our aim is to explore their bacteriostatic components. HS-SPME-GC-MS technology was used to analyze the volatiles produced by the C. fimbriata strain (WJSK-1, Mby). Postharvest cherry tomato fruit black rot caused by A. alternata was treated both in vitro and in vivo, with pure individual components produced by C. fimbriata. The benzaldehyde, nonanal, 2-Phenylethanol, and isoamyl acetate from C. fimbriata can effectively inhibit growth of A. alternata, and delay disease. It has the potential to be developed as a new type of fumigant, a potential replacement for fungicides in the future.

Identification and functional studies of microbial volatile organic compounds produced by Arctic flower yeasts

Microbial volatile organic compounds (mVOCs) can serve as a communication channel among microorganisms, insects and plants, making them important in ecosystem. In order to understand the possible role of mVOCs in Arctic ecology, the microbes in Arctic flowers and their mVOCs and effects on plants were investigated. This study aims to isolate different yeast species from the flowers of five Arctic plant species and further to explore the function of mVOCs emitted by these microbes to plant. It was found that the composition and amount of mVOCs produced by the isolated yeasts were considerably affected by changes in incubation temperature. When the incubation temperature rose, the species of alcohols, aldehydes, esters, organic acids, and ketones increased, but substances specific to low temperature decreased or disappeared. When yeasts were co-cultured with Arabidopsis thaliana without any direct contact, mVOCs produced by the isolated yeasts inhibited the seed germination of A. thaliana at low temperatures; however, the mVOCs promoted the chlorophyll content, fresh weight, root weight and flowering rate of Arabidopsis plants. Although the overall growth-promoting effect of yeast mVOCs was higher at 20°C than at 10°C, the growth-promoting effect on roots, flowers and chlorophyll was highest at 10°C. When cultured at 10°C, the mVOCs produced by Cystofilobasidium capitatum A37, Cryptococcus sp. D41, and Sporidiobolus salmonicolor D27 had the highest growth-promoting effects on the root, flowering rate and chlorophyll content of Arabidopsis, respectively. In the co-culture system, some new mVOCs were detected, such as hendecane, tetradecane, and 1-hexanol that have been proven to promote plant growth. In addition, mVOCs of the isolated Arctic yeasts could inhibit the growth of several microorganisms, especially filamentous fungi. It was the first time to prove that mVOCs produced by the isolated yeasts had varying effects on plant growth at different incubating temperatures, providing a reference for the interactions between microorganisms and plants and their possible responses to climate change in the Arctic area. Moreover, the characteristics of promoting plant growth and inhibiting microbial growth by mVOCs of Arctic yeasts would lay a foundation for potential applications in the future.

Volatile Organic Compounds (VOCs) Produced by Gluconobacter cerinus and Hanseniaspora osmophila Displaying Control Effect against Table Grape-Rot Pathogens

Table grapes (Vitis vinifera) are affected by botrytis bunch rot and summer bunch rot, the latter a complex disease caused by Botrytis cinerea, Aspergillus spp., Penicillium expansum and Rhizopus stolonifer. To search for biocontrol alternatives, a new bioproduct composed of Gluconobacter cerinus and Hanseniaspora osmophila, a consortium called PUCV-VBL, was developed for the control of fungal rots in table grapes. Since this consortium presents new biocontrol species, the effect of their VOCs (volatile organic compounds) was evaluated under in vitro and in vivo conditions. The VOCs produced by the PUCV-VBL consortium showed the highest mycelial inhibition against Botrytis cinerea (86%). Furthermore, H. osmophila was able to inhibit sporulation of A. tubingensis and P. expansum. VOCs' effect in vivo was evaluated using berries from Red Globe, Thompson Seedless and Crimson Seedless grapes cultivars, demonstrating a mycelial inhibition by VOCs greater than 70% for all evaluated fungal species. The VOC identification of the PUCV-VBL consortium was analyzed by solid-phase microextraction coupled to gas chromatography-mass spectrometry (SPME-GCMS). A total 26 compounds were identified, including 1-butanol 3-methyl, propanoic acid ethyl ester, ethyl acetate, phenylethyl alcohol, isobutyl acetate and hexanoic acid ethyl ester. Our results show that VOCs are an important mode of action of the PUCV-VBL biological consortium.

Antifungal Activity of Volatile Organic Compounds Produced by Bacillus methylotrophicus and Bacillus thuringiensis against Five Common Spoilage Fungi on Loquats

Loquat fruit is one of the most perishable fruits in China, and has a very limited shelf life because of mechanical injury and microbial decay. Due to an increasing concern about human health and environmental security, antagonistic microorganisms have been a potential alternative for fungicides to control postharvest diseases. In this work, the antifungal effect of volatile organic compounds (VOCs) produced by Bacillus methylotrophicus BCN2 and Bacillus thuringiensis BCN10 against five postharvest pathogens isolated from loquat fruit, Fusarium oxysporum, Botryosphaeria sp., Trichoderma atroviride, Colletotrichum gloeosporioides, and Penicillium expansum were evaluated by in vitro and in vivo experiments. As a result, the VOCs released by BCN2 and BCN10 were able to suppress the mycelial growth of all targeted pathogens according to inhibition ratio in the double petri-dish assay as well as disease incidence and disease diameter on loquat fruits. The main volatile compounds were identified by solid-phase microextraction (SPME)-gas chromatography. These VOCs produced by the two strains played complementary roles in controlling these five molds and enabled loquat fruits to keep fresh for ten days, significantly. This research will provide a theoretic foundation and technical support for exploring the functional components of VOCs applicable in loquat fruit preservation.

Aureobasidium pullulans volatilome identified by a novel, quantitative approach employing SPME-GC-MS, suppressed Botrytis cinerea and Alternaria alternata in vitro

Volatile organic compounds (VOCs) produced by Aureobasidium pullulans were investigated for antagonistic actions against Alternaria alternata and Botrytis cinerea. Conidia germination and colony growth of these two phytopathogens were suppressed by A. pullulans VOCs. A novel experimental setup was devised to directly extract VOCs using solid-phase microextraction-gas chromatography-mass spectrometry (SPME-GC-MS) from antagonist-pathogen culture headspace. The proposed system is a robust method to quantify microbial VOCs using an internal standard. Multivariate curve resolution-alternating least squares deconvolution of SPME-GC-MS spectra identified fourteen A. pullulans VOCs. 3-Methyl-1-hexanol, acetone, 2-heptanone, ethyl butyrate, 3-methylbutyl acetate and 2-methylpropyl acetate were newly identified in A. pullulans headspace. Partial least squares discriminant analysis models with variable importance in projection and selectivity ratio identified four VOCs (ethanol, 2-methyl-1-propanol, 3-methyl-1-butanol and 2-phenylethanol), with high explanatory power for discrimination between A. pullulans and pathogen. The antifungal activity and synergistic interactions of the four VOCs were evaluated using a Box-Behnken design with response surface modelling. Ethanol and 2-phenylethanol are the key inhibitory A. pullulans VOCs against both B. cinerea and A. alternata. Our findings introduce a novel, robust, quantitative approach for microbial VOCs analyses and give insights into the potential use of A. pullulans VOCs to control B. cinerea and A. alternata.

Aureobasidium pullulans volatile organic compounds as alternative postharvest method to control brown rot of stone fruits

Volatile compounds produced by L1 and L8 strains were assayed against mycelia and conidia growth of Monilinia laxa, M. fructicola, M. polystroma, and M. fructigena of stone fruits. Results showed that volatile metabolites inhibited significantly pathogens growth, in particular M. fructigena mycelium growth (70% by L1 and 50% by L8) and M. fructicola conidia germination (85% by L1 and 70% by L8) compared to the control. Moreover, the antagonistic activity was enhanced by the addition of asparagine (120 mg L^-1) in the culture media composition. Synthetic pure compounds were tested in vitro on pathogens mycelial and conidia growth and their EC₅₀ values were estimated, confirming 2-phenethyl as the most active compound. For this reason 2-phenethyl and VOCs of both yeast strains were assayed in vivo on cherry, peach, and apricot fruits. Regarding peach fruit, both treatments, yeasts and pure compounds, displayed the best inhibiting action against all the pathogens especially against M. laxa (100% by L1, 84% by L8 and 2-phenethyl). ATR/IR spectroscopy analysis showed how VOCs produced by both strains increase the fruit waxes complexity reducing the pathogens attack so playing an essential role in the antagonistic activity of both yeast strains and on fruit structural composition.

Effect of Marine Bacteria and Ulvan on the Activity of Antioxidant Defense Enzymes and the Bio-Protection of Papaya Fruit against Colletotrichum gloeosporioides

Anthracnose, caused by Colletotrichum gloeosporioides, is one of the most important diseases in papaya fruit. Its control has been achieved with synthetic fungicides, but the application of marine bacteria and the sulphated polysaccharide ulvan (structural description: β[1,4]-D-GlcA-α[1,4]-L-Rha 3 sulfate, β[1,4]-L-IdoA-α[1,4]-L-Rha 3 sulfate, β[1,4]-D-Xyl-α[1,4]-L-Rha 3 sulfate, and β[1,4]-D-Xyl 2-sulfate-α[1,4]-L-Rha 3 sulfate) from Ulva sp. can be an alternative in the use of agrochemicals. Thus, the objective of this study was to assess the effect in vitro and in vivo of two marine bacteria, Stenotrophomonas rhizophila and Bacillus amyloliquefaciens, and ulvan in papaya fruit’s bio-protection against C. gloeosporioides. The capacity of marine bacteria to inhibit mycelial growth and phytopathogen spore germination in vitro through volatile organic compounds (VOCs) and carbohydrate competition was evaluated. Fruit was inoculated with bacteria, ulvan, and C. gloeosporioides and incubated at 25 °C and 90% of relative humidity (RH) for seven days. Disease incidence (%), lesion diameter (mm), and antioxidant defense enzyme activity (such as superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) were quantified. In vitro, C. gloeosporioides was inhibited by S. rhizophila and B. amyloliquefaciens. In vivo, disease incidence and the lesion diameter of anthracnose on papaya fruit were significantly reduced by marine bacteria and ulvan. Antioxidant defense enzyme activity played an important role in fruit bio-protection against C. gloeosporioides. The application of marine bacteria and ulvan can be an alternative in the sustainable postharvest management of papaya.

Postharvest biocontrol of Colletotrichum gloeosporioides on mango using the marine bacterium Stenotrophomonas rhizophila and its possible mechanisms of action

The marine bacterium Stenotrophomonas rhizophila was assessed in vitro and in vivo as biocontrol agent against anthracnose disease of mango fruit caused by Colletotrichum gloeosporioides. The results showed that in vitro inhibition of the colony diameter and spore germination of the phytopathogen was due to the production of VOCs, competition for nutrients, and lytic enzymes. When a concentration of 1 × 10⁸ cells ml^-1 of the antagonist bacterium was applied to the fruit, disease incidence was reduced by 95%, and the lesion diameter of anthracnose decreased by 85%, which offered greater protection than the synthetic fungicide. This is the first report of antagonistic mechanisms of the marine bacterium S. rhizophila against anthracnose disease in mango, which in this study was found to be more effective than the synthetic fungicide.

Leaves of Indoor Ornamentals Are Biodiversity and Functional Hotspots for Fungi

Leaf-inhabiting fungi are an important, but often overlooked component of molecular biodiversity studies. To understand their diversity and function in relation to plant species and climate, the phyllospheres of 14 phylogenetically diverse ornamental plant species were analyzed under different controlled greenhouse conditions. We found unexpectedly high fungal diversity (H' = 2.8-6.5), OTU numbers (449-1050) and abundances (103-106 CFU cm-2 leaf surface) associated with all plants studied indoors. Despite experimental limitations, the composition of fungal communities were inclined toward a plant species-dependent pattern compared to the ambient climatic variables. Most detected fungi were patho- and saprotrophs showing a yeast-like growth morphology and were associated to the groups of endophytes and potential plant pathogens in a plant species-specific manner. A representative strain collection showed that 1/3 of the tested fungi (mainly Penicillium, Cladosporium, and Cryptococcus spp.) were able to inhibit mycelial growth and 2/3 inhibit sporulation of the plant pathogen Botrytis cinerea by the production of antifungal volatile organic compounds (VOCs) completely. This study indicates that plant leaves harbor a stable phyllosphere fungal diversity in diverse microclimates and enrich distinctive functional guilds.

Mining the Volatilomes of Plant-Associated Microbiota for New Biocontrol Solutions

Microbial lifeforms associated with land plants represent a rich source for crop growth- and health-promoting microorganisms and biocontrol agents. Volatile organic compounds (VOCs) produced by the plant microbiota have been demonstrated to elicit plant defenses and inhibit the growth and development of numerous plant pathogens. Therefore, these molecules are prospective alternatives to synthetic pesticides and the determination of their bioactivities against plant threats could contribute to the development of control strategies for sustainable agriculture. In our previous study we investigated the inhibitory impact of volatiles emitted by Pseudomonas species isolated from a potato field against the late blight-causing agent Phytophthora infestans. Besides the well-documented emission of hydrogen cyanide, other Pseudomonas VOCs impeded P. infestans mycelial growth and sporangia germination. Current advances in the field support the emerging concept that the microbial volatilome contains unexploited, eco-friendly chemical resources that could help select for efficient biocontrol strategies and lead to a greener chemical disease management in the field.

Antifungal Microbial Agents for Food Biopreservation-A Review

Food spoilage is a major issue for the food industry, leading to food waste, substantial economic losses for manufacturers and consumers, and a negative impact on brand names. Among causes, fungal contamination can be encountered at various stages of the food chain (e.g., post-harvest, during processing or storage). Fungal development leads to food sensory defects varying from visual deterioration to noticeable odor, flavor, or texture changes but can also have negative health impacts via mycotoxin production by some molds. In order to avoid microbial spoilage and thus extend product shelf life, different treatments—including fungicides and chemical preservatives—are used. In parallel, public authorities encourage the food industry to limit the use of these chemical compounds and develop natural methods for food preservation. This is accompanied by a strong societal demand for ‘clean label’ food products, as consumers are looking for more natural, less severely processed and safer products. In this context, microbial agents corresponding to bioprotective cultures, fermentates, culture-free supernatant or purified molecules, exhibiting antifungal activities represent a growing interest as an alternative to chemical preservation. This review presents the main fungal spoilers encountered in food products, the antifungal microorganisms tested for food bioprotection, and their mechanisms of action. A focus is made in particular on the recent in situ studies and the constraints associated with the use of antifungal microbial agents for food biopreservation.

Metabolomic and Transcriptomic Comparison of Solid-State and Submerged Fermentation of Penicillium expansum KACC 40815

Penicillium spp. are known to harbor a wide array of secondary metabolites with cryptic bioactivities. However, the metabolomics of these species is not well-understood in terms of different fermentation models and conditions. The present study involved metabolomics profiling and transcriptomic analysis of Penicillium expansum 40815 under solid-state fermentation (SSF) and submerged fermentation (SmF). Metabolite profiling was carried out using ultra-performance liquid chromatography quadruple time-of-flight mass spectrometry with multivariate analysis, followed by transcriptomic analyses of differentially expressed genes. In principal component analysis, the metabolite profiling data was studied under different experimental sets, including SSF and SmF. The significantly different metabolites such as polyketide metabolites (agonodepside B, rotiorin, verrucosidin, and ochrephilone) and corresponding gene transcripts (polyketide synthase, aromatic prenyltransferase, and terpenoid synthase) were primarily detected under SmF conditions. In contrast, the meroterpenoid compounds (andrastin A and C) and their genes transcripts were exclusively detected under SSF conditions. We demonstrated that the metabolite production and its corresponding gene expression levels in P. expansum 40815 were significantly influenced by the varying growth parameters and the immediate environment. This study further provides a foundation to produce specific metabolites by regulating fermentation conditions.