Fungal volatile organic compounds: A review with emphasis on their biotechnological potential

Volatilome of the maize phytopathogenic fungus Fusarium verticillioides: potential applications in diagnosis and biocontrol

BACKGROUND

Fusarium verticillioides is a maize fungal phytopathogen and a producer of volatile organic compounds (VOCs) and fumonisin B1 (FB1). Our aim was to study the volatilome, conidial production, ergosterol and FB1 biosynthesis in maize cultures over a 30-day incubation period (5, 10, 15, 20, 25, 30 days post inoculation [DPI]). The effect of pure VOCs on the same parameters was then evaluated to study their potential role as biocontrol agents.

RESULTS

In total, 91 VOCs were detected, with volatile profiles being more similar between 5 and 10 DPI compared with 15, 20, 25 and 30 DPI. Ergosterol content increased steadily with incubation time, and three growth stages were identified: a lag phase (0 to 15 DPI), an exponential phase (15 to 20 DPI) and a stationary phase (20 to 30 DPI). The maximum concentration of FB1 was detected at 25 (0.030 μg FB1/μg ergosterol) and 30 DPI (0.037 μg FB1/μg ergosterol), whereas conidial production showed a maximum value at 15 DPI (4.3 ± 0.2 × 105 conidia/μg ergosterol). Regarding pure VOCs, minimal inhibitory concentration values ranged from 0.3 mm for 4-hexen-3-one to 7.4 mm for 2-undecanone. Pure VOCs reduced radial growth, conidial production and ergosterol and FB1 biosynthesis.

CONCLUSIONS

The marked resemblance between VOC profiles at 5 and 10 DPI suggests that they could act as early indicators of fungal contamination, particularly 4-ethylguaiacol, 4-ethyl-2-methoxyanisole, heptanol and heptyl acetate. On the other hand, their role as inhibitors of fungal growth and FB1 biosynthesis prove their great potential as safer alternatives to control phytopathogenic fungi. © 2024 Society of Chemical Industry.

Endophytic Fungi: A Treasure Trove of Antifungal Metabolites

Emerging and reemerging fungal infections are very common in nosocomial and non-nosocomial settings in people having poor immunogenic profiles either due to hematopoietic stem cell transplants or are using immunomodulators to treat chronic inflammatory disease or autoimmune disorders, undergoing cancer therapy or suffering from an immune weakening disease like HIV. The refractory behavior of opportunistic fungi has necessitated the discovery of unconventional antifungals. The emergence of black fungus infection during COVID-19 also triggered the antifungal discovery program. Natural products are one of the alternative sources of antifungals. Endophytic fungi reside and co-evolve within their host plants and, therefore, offer a unique bioresource of novel chemical scaffolds with an array of bioactivities. Hence, immense possibilities exist that these unique chemical scaffolds expressed by the endophytic fungi may play a crucial role in overcoming the burgeoning antimicrobial resistance. These chemical scaffolds so expressed by these endophytic fungi comprise an array of chemical classes beginning from cyclic peptides, sesquiterpenoids, phenols, anthraquinones, coumarins, etc. In this study, endophytic fungi reported in the last six years (2018-2023) have been explored to document the antifungal entities they produce. Approximately 244 antifungal metabolites have been documented in this period by different groups of fungi existing as endophytes. Various aspects of these antifungal metabolites, such as antifungal potential and their chemical structures, have been presented. Yet another unique aspect of this review is the exploration of volatile antifungal compounds produced by these endophytic fungi. Further strategies like epigenetic modifications by chemical as well as biological methods and OSMAC to induce the silent gene clusters have also been presented to generate unprecedented bioactive compounds from these endophytic fungi.

Review: Strategies and technologies in preventing regulated and emerging mycotoxin co-contamination in forage for safeguarding ruminant health

Ruminants are often considered less susceptible to mycotoxins than monogastrics, owing to rumen microflora converting mycotoxins to less toxic compounds or several compounds present in the rumen-reticulum compartment, being able to bind the mycotoxin "mother" molecule that make them unavailable for absorption process in the gastro-intestinal tract of host animals. However, if ruminants consume feed contaminated by mycotoxins for long periods, their growth, development, and fertility can be compromised. Among regulated mycotoxins, the most studied and known for their effects are aflatoxins (AFs) AFB1, AFB2, AFG1 and AFG2, as well as the AFM1 for its high importance in dairy sector, deoxynivalenol (DON) and its metabolites 3/15 acetyl-DON and 3-glucoside DON, T-2 and HT-2 toxins, zearalenone, fumonisins, in particular that belong to the B class, and ochratoxin A. Furthermore, because of the emergence of multiple emerging mycotoxins that are detectable in feed utilised in ruminant diets, such as ensiled forage, there is now a growing focus on investigating these compounds by the scientific community to deepen their toxicity for animal health. Despite the enhancement of research, it is remarkable that there is a paucity of in vivo trials, as well as limited studies on nutrient digestibility and the impact of these molecules on rumen and intestinal functions or milk yield and quality. In this review, recent findings regarding the occurrence of regulated and emerging mycotoxins in forage and their possible adverse effects on dairy cattle are described, with special emphasis on animal performance and on rumen functionality.

Self-inhibition of growth and allelopathy through volatile organic compounds in Fusarium solani and Aspergillus fumigatus

Microbial volatile organic compounds (VOCs) emitted from fungi are known as their secondary metabolites from environmental sources. However, their physiological roles remain to be unclear. Even though the roles are still unknown, VOCs are deliberately released to convey information to both homologous and non-homologous organisms. We investigated the effects of single VOCs (hexanal, benzaldehyde, heptanal, 2-ethyl-1-hexanol, 3-octanone, 2-undecanone, 3-octanol, 2-Phenylethanol, 2-phenyl-2-propanol, phenylbenzaldehyde, 2-pentadecanone, β-trans-bergamotene, β-bisabolene, 2-methyl-5 -(1-methylethyl)pyrazine) on the fungal growth. In parallel, application of the co-culturing system in a growth chamber allowed free gas and VOCs exchange between emitter colonies of Fusarium solani and Aspergillus fumigatus, or between colonies of different growth stages of the same species. Distinct self-inhibition occurred by the emitters of fungal growing colonies against receiver ones on the stage of conidial germination or against the younger colonies at an earlier stage in both fungi. Similarly, the phenomenon of allelopathy appeared to work between growing colonies of F. solani and the germinating conidia or young colonies of A. fumigatus or vice versa. Solid phase microextraction-gas chromatography/mass spectrometry revealed VOCs compounds of each fungi. In F. solani, hexanal and benzaldehyde appeared to be significant inhibitors for colony growth. Benzaldehyde inhibited filamentous growth but not conidial germination. In A. fumigatus, heptanal seemed to be an equivalent effector. The inhibitory effect of benzaldehyde was more distinct on the A. fumigatus conidial germination than its filamentous growth.

Volatile Organic Compounds from Ceratocystis cacaofunesta, a Causal Agent of Ceratocystis Wilt of Cacao

Fungi of the genus Ceratocystis are aggressive tree pathogens that cause serious diseases in several crops around the world. Ceratocystis wilt disease caused by C. cacaofunesta has been shown to be responsible for severe reductions in cacao production. In this study, headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography-mass spectrometry (GC-MS) was used in combination with chemometric analysis for monitoring volatile organic compounds (VOCs) released from C. cacaofunesta. Low-molecular-weight esters, alcohols, ketones, and sulphur compounds were identified in the liquid broth. Monitoring the volatile profile over five days of fungal growth revealed that the concentrations of alcohol and esters were inversely proportional. Acetate esters were responsible for the intense fruity aroma of the C. cacaofunesta culture produced within the first hours after fungal inoculation, which decreased over time, and are likely associated with the attraction of insect vectors to maintain the life cycle of the pathogen. PCA revealed that 3-methylbutyl acetate was the metabolite with the highest factor loading for the separation of the VOC samples after 4 h of fungal growth, whereas ethanol and 3-methylbutan-1-ol had the highest factor loadings after 96 and 120 h. 3-Methylbutan-1-ol is a phytotoxic compound that is likely associated with host cell death since C. cacaofunesta is a necrotrophic fungus. Fungal VOCs play important roles in natural habitats, regulating developmental processes and intra- and interkingdom interactions. This is the first report on the volatiles released by C. cacaofunesta.

Qualitative and Untargeted Volatilome Fingerprinting of Aspergillus sp. and Bulbithecium sp. by HS-SPME-GCMS and Functional Interactions

Research on fungal volatile organic compounds (VOCs) has increased worldwide in the last 10 years, but marine fungal volatilomes remain underexplored. Similarly, the hormone-signaling pathways, agronomic significance, and biocontrol potential of VOCs in plant-associated fungi make the area of research extremely promising. In the current investigation, VOCs of the isolates-Aspergillus sp. GSBT S13 and GSBT S14 from marine sediments, and Bulbithecium sp. GSBT E3 from Eucalyptus foliage were extracted using Head Space solid phase microextraction, followed by gas chromatography-mass spectrometry, identification, statistical analyses, and prediction of functions by KEGG COMPOUND and STITCH 5.0 databases. The significance of this research is fingerprinting VOCs of the isolates from distinct origins, identification of compounds using three libraries (NIST02, NIST14, and W9N11), and using bioinformatic tools to perform functional analysis. The most important findings include the identification of previously unreported compounds in fungi-1-methoxy naphthalene, diethyl phthalate, pentadecane, pristane, and nonanal; the prediction of the involvement of small molecules in the degradation of aromatic compound pathways and activation, inhibition, binding, and catalysis of metabolites with predicted protein partners. This study has ample opportunity to validate the findings and understand the mechanism or mode of action, the interspecies interactions, and the role of the metabolites in geochemical cycles.

Yeasts volatile organic compounds (VOCs) as potential growth enhancers and molds biocontrol agents of mushrooms mycelia

Volatile organic compounds (VOCs) produced by yeasts can positively affect crops, acting as antifungals or biostimulants. In this study, Aureobasidium pullulans and Metschnikowia pulcherrima were evaluated as potential antagonists of Trichoderma spp., common fungal pathogen in mushroom cultivation. To assess the biocontrol ability and biostimulant properties of the selected yeast species, in vitro co-culture and VOCs exposure assays were conducted. In both assays, VOCs produced by Aureobasidium spp. showed the stronger antifungal activity with a growth inhibition up to 30 %. This result was further confirmed by the higher volatilome alcohol content revealed by solid phase microextraction-gas chromatography mass spectrometry (SPME/GC-MS). Overall, Aureobasidium strains can be potentially used as biocontrol agent in Pleorotus ostreatus and Cyclocybe cylindracea mycelial growth, without affecting their development as demonstrated by VOCs exposure assay and Fourier-transform infrared spectroscopy (FT-IR). Conversely, M. pulcherrima was characterized by a lower or absent antifungal properties and by a volatilome composition rich in isobutyl acetate, an ester often recognized as plant growth promoter. As confirmed by FT-IR, Lentinula mycelia exposed to M. pulcherrima VOCs showed a higher content of proteins and lipids, suggesting an improvement of some biochemical properties. Our study emphasizes that VOCs produced by specific yeast strains are potentially powerful alternative to synthetic fungicide in the vegetative growth of mushroom-forming fungi and also able to modify their biochemical composition.

Allochthonous Trichoderma Isolates Boost Atractylodes lancea Herb Quality at the Cost of Rhizome Growth

Atractylodes lancea is a perennial herb whose rhizome (AR) is a valuable traditional Chinese medicine with immense market demand. The cultivation of Atractylodes lancea faces outbreaks of root rot and deterioration in herb quality due to complex causes. Here, we investigated the effects of Trichoderma spp., well-known biocontrol agents and plant-growth-promoters, on ARs. We isolated Trichoderma strains from healthy ARs collected in different habitats and selected three T. harzianum strains (Th2, Th3 and Th4) with the strongest antagonizing effects on root rot pathogens (Fusarium spp.). We inoculated geo-authentic A. lancea plantlets with Th2, Th3 and Th4 and measured the biomass and quality of 70-day-old ARs. Th2 and Th3 promoted root rot resistance of A. lancea. Th2, Th3 and Th4 all boosted AR quality: the concentration of the four major medicinal compounds in ARs (atractylon, atractylodin, hinesol and β-eudesmol) each increased 1.6- to 18.2-fold. Meanwhile, however, the yield of ARs decreased by 0.58- to 0.27-fold. Overall, Th3 dramatically increased the quality of ARs at a relatively low cost, namely lower yield, showing great potential for practical application. Our results showed selectivity between A. lancea and allochthonous Trichoderma isolates, indicating the importance of selecting specific microbial patches for herb cultivation.

Detecting Pathogenic Phytophthora Species Using Volatile Organic Compounds

There are several highly damaging Phytophthora species pathogenic to forest trees, many of which have been spread beyond their native range by the international trade of live plants and infested materials. Such introductions can be reduced through the development of better tools capable of the early, rapid, and high-throughput detection of contaminated plants. This study utilized a volatilomics approach (solid-phase microextraction coupled to gas chromatography-mass spectrometry) to differentiate between several Phytophthora species in culture and discriminate between healthy and Phytophthora-inoculated European beech and pedunculate oak trees. We tentatively identified 14 compounds that could differentiate eight Phytophthora species from each other in vitro. All of the Phytophthora species examined, except Phytophthora cambivora, uniquely produced at least one compound not observed in the other species; however, most detected compounds were shared between multiple species. Phytophthora polonica had the most unique compounds and was the least similar of all the species examined. The inoculated seedlings had qualitatively different volatile profiles and could be distinguished from the healthy controls by the presence of isokaurene, anisole, and a mix of three unknown compounds. This study supports the notion that volatiles are suitable for screening plant material, detecting tree pathogens, and differentiating between healthy and diseased material.

Chemical Ecology and Management of Dengue Vectors

Dengue, caused by the dengue virus, is the most widespread arboviral infectious disease of public health significance globally. This review explores the communicative function of olfactory cues that mediate host-seeking, egg-laying, plant-feeding, and mating behaviors in Aedes aegypti and Aedes albopictus, two mosquito vectors that drive dengue virus transmission. Aedes aegypti has adapted to live in close association with humans, preferentially feeding on them and laying eggs in human-fabricated water containers and natural habitats. In contrast, Ae. albopictus is considered opportunistic in its feeding habits and tends to inhabit more vegetative areas. Additionally, the ability of both mosquito species to locate suitable host plants for sugars and find mates for reproduction contributes to their survival. Advances in chemical ecology, functional genomics, and behavioral analyses have improved our understanding of the underlying neural mechanisms and reveal novel and specific olfactory semiochemicals that these species use to locate and discriminate among resources in their environment. Physiological status; learning; and host- and habitat-associated factors, including microbial infection and abundance, shape olfactory responses of these vectors. Some of these semiochemicals can be integrated into the toolbox for dengue surveillance and control.

Profiling of Volatile Compounds in 'Muscat Hamburg' Contaminated with Aspergillus carbonarius before OTA Biosynthesis Based on HS-SPME-GC-MS and DLLME-GC-MS

Aspergillus carbonarius is known to produce the carcinogenic ochratoxin A (OTA) in grapes. The metabolism process before OTA biosynthesis influences the content and composition of the volatile compounds in grapes. In this study, a self-established method based on QuEChERS coupled with high-performance liquid chromatography-fluorescence detection (HPLC-FLD) was used to determine the OTA levels during a seven-day contamination period. The results showed that OTA was detected on the second day after contamination with A. carbonarius. Thus, the first day was considered as the critical sampling timepoint for analyzing the volatiles in grapes before OTA biosynthesis. Additionally, the volatile compounds in grapes were analyzed using headspace solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC-MS) and dispersive liquid-liquid microextraction gas chromatography-mass spectrometry (DLLME-GC-MS). The corresponding data were evaluated via multivariate data analysis using projection methods, including PCA and OPLS-DA. The results indicated significant differences in the nine volatile compounds in grapes contaminated with A. carbonarius before OTA biosynthesis. The results of the Pearson correlation analysis showed positive correlations between ethyl acetate, styrene, 1-hexanol and OTA; (E)-2-hexenal and nerolic acid were negatively correlated with OTA. Overall, these findings provide a theoretical basis for the early prediction of OTA formation in grape and grape products using GC-MS technology.

Fermentation Characteristics, Antinutritional Factor Level and Flavor Compounds of Soybean Whey Yogurt

Soybean whey contains high levels of off-flavors and anti-nutritional factors and is generally considered unsuitable for direct application in the food industry. In this work, to reduce beany off-flavors and anti-nutritional factors, and to improve its fermentation characteristics, soybean whey was treated with electrodialysis desalination, vacuum concentration and lactic acid bacteria (LAB) fermentation. The results showed that electrodialysis desalination increased the fermentation rate and the number of viable lactic acid bacteria of soybean whey yogurt. More than 90% of the antinutritional factor level (urease and trypsin inhibitory activity) was removed due to high-temperature denaturation inactivation and LAB degradation. Concentrated desalted soybean whey yogurt (CDSWY) possessed larger values for firmness and consistency, and a denser network microstructure compared with undesalted yogurt. Over 90% of off-flavors including hexanal, 1-octen-3-ol and 1-octen-3-one were removed after electrodialysis desalination and concentration treatment. Meanwhile, the newly generated β-damascenone through carotenoid degradation and 2,3-butanedione improved the pleasant flavor and sensory quality of CDSWY, while the salty taste of CSWY lowered its sensory quality. This study provided a theoretical basis for better utilization of soybean whey to develop a plant-based yogurt like dairy yogurt.

In Vitro Analysis of the Antagonistic Biological and Chemical Interactions between the Endophyte Sordaria tomento-alba and the Phytopathogen Botrytis cinerea

Plant pathogenic infections causing substantial global food losses are a persistent challenge. This study investigates a potential biocontrol strategy against the necrotrophic fungus Botrytis cinerea using the endophytic fungus Sordaria tomento-alba isolated from Gliricidia sepium in Colombia. Today, synthetic fungicides dominate B. cinerea control, raising environmental and health concerns. S. tomento-alba exhibits notable in vitro effects, inhibiting B. cinerea growth by approximately 60% during co-culture and 50% in double disc co-culture. Additionally, it suppresses botryanes production and produces the compound heptacyclosordariolone, which has proven effective in inhibiting B. cinerea mycelial growth and spore germination in vitro. This biocontrol agent could be a potential eco-friendly alternative to replace synthetic fungicides. Our study provides insights into the chemical and biological mechanisms underpinning the antagonistic activity of S. tomento-alba, emphasizing the need for further research to understand its biosynthesis pathways and optimize its biocontrol potential. It also contributes molecular evidence of fungal interactions with implications for advanced forums in molecular studies in biology and chemistry, particularly in addressing plant pathogenic infections and promoting sustainable agriculture.

Cross-talk between immunity and behavior: insights from entomopathogenic fungi and their insect hosts

Insects are one of the most successful animals in nature, and entomopathogenic fungi play a significant role in the natural epizootic control of insect populations in many ecosystems. The interaction between insects and entomopathogenic fungi has continuously coevolved over hundreds of millions of years. Many components of the insect innate immune responses against fungal infection are conserved across phyla. Additionally, behavioral responses, which include avoidance, grooming, and/or modulation of body temperature, have been recognized as important mechanisms for opposing fungal pathogens. In an effort to investigate possible cross-talk and mediating mechanisms between these fundamental biological processes, recent studies have integrated and/or explored immune and behavioral responses. Current information indicates that during discrete stages of fungal infection, several insect behavioral and immune responses are altered simultaneously, suggesting important connections between the two systems. This review synthesizes recent advances in our understanding of the physiological and molecular aspects influencing cross-talk between behavioral and innate immune antifungal reactions, including chemical perception and olfactory pathways.

Breaking barriers in Candida spp. detection with Electronic Noses and artificial intelligence

The timely and accurate diagnosis of candidemia, a severe bloodstream infection caused by Candida spp., remains challenging in clinical practice. Blood culture, the current gold standard technique, suffers from lengthy turnaround times and limited sensitivity. To address these limitations, we propose a novel approach utilizing an Electronic Nose (E-nose) combined with Time Series-based classification techniques to analyze and identify Candida spp. rapidly, using culture species of C. albicans, C.kodamaea ohmeri, C. glabrara, C. haemulonii, C. parapsilosis and C. krusei as control samples. This innovative method not only enhances diagnostic accuracy and reduces decision time for healthcare professionals in selecting appropriate treatments but also offers the potential for expanded usage and cost reduction due to the E-nose's low production costs. Our proof-of-concept experimental results, carried out with culture samples, demonstrate promising outcomes, with the Inception Time classifier achieving an impressive average accuracy of 97.46% during the test phase. This paper presents a groundbreaking advancement in the field, empowering medical practitioners with an efficient and reliable tool for early and precise identification of candidemia, ultimately leading to improved patient outcomes.

Fungal Cultivars of Higher Attine Ants Promote Escovopsis Chemotropism

In varied environments, microorganisms search for partners or nutritional resources using chemical signals. Microbes are drawn (chemotaxis) or grow directionally (chemotropism) towards the chemical source, enabling them to establish and maintain symbiosis. The hypocrealean fungi Escovopsis enhance their growth towards the basidiomycete fungus Leucoagaricus gongylophorus, which is cultivated by leaf-cutting attine ants for food. Although directional growth is well documented in this symbiosis, it is unclear whether non-volatile or volatile organic compounds participate in the interaction between cultivar and Escovopsis, and which specific chemical compounds might attract and induce chemotropism. In this study, we examined the growth responses of Escovopsis isolates to non-volatile and volatile organic compounds produced by fungal cultivars of higher attine ants. We also isolated and identified molecules released by the ant-cultivar and assessed the chemotropism of Escovopsis towards them. Our results indicate that the growth of Escovopsis is stimulated in the presence of both non-volatile and volatile compounds from fungal cultivars. We also identified three isomeric diketopiperazines molecules from crude extracts of the ant cultivar, suggesting that these might play a role in Escovopsis chemotropism. Our findings provide insights into the complex chemical interactions that govern the association between Escovopsis and fungal cultivars.

Mechanistic insights into the role of actinobacteria as potential biocontrol candidates against fungal phytopathogens

Worldwide mounting demand for better food production to nurture exasperating population emphasizes on reduced crop losses. The incidence of pathogens into the agricultural fields has tend to dwindle plethora of cereal, vegetable, and other fodder crops. This, in turn, has seriously impacted the economic losses on global scale. Apart from this, it is quite challenging to feed the posterity in the coming decades. To counteract this problem, various agrochemicals have been commercialized in the market that no doubt shows positive results but along with adversely affecting the ecosystem. Therefore, the excessive ill-fated use of agrochemicals to combat the plant pests and diseases highlights that alternatives to chemical pesticides are need of the hour. In recent days, management of plant diseases using plant-beneficial microbes is gaining interest as safer and potent alternatives to replace chemically based pesticides. Among these beneficial microbes, actinobacteria especially streptomycetes play considerable role in combating plant diseases along with promoting the plant growth and development along with their productivity and yield. The mechanisms exhibited by actinobacteria include antibiosis (antimicrobial compounds and hydrolytic enzymes), mycoparasitism, nutrient competition, and induction of resistance in plants. Thus, in cognizance with potential of actinobacteria as potent biocontrol agents, this review summarizes role of actinobacteria and the multifarious mechanisms exhibited by actinobacteria for commercial applications.

Fertilization of Microbial Composts: A Technology for Improving Stress Resilience in Plants

Microbial compost plays a crucial role in improving soil health, soil fertility, and plant biomass. These biofertilizers, based on microorganisms, offer numerous benefits such as enhanced nutrient acquisition (N, P, and K), production of hydrogen cyanide (HCN), and control of pathogens through induced systematic resistance. Additionally, they promote the production of phytohormones, siderophore, vitamins, protective enzymes, and antibiotics, further contributing to soil sustainability and optimal agricultural productivity. The escalating generation of organic waste from farm operations poses significant threats to the environment and soil fertility. Simultaneously, the excessive utilization of chemical fertilizers to achieve high crop yields results in detrimental impacts on soil structure and fertility. To address these challenges, a sustainable agriculture system that ensures enhanced soil fertility and minimal ecological impact is imperative. Microbial composts, developed by incorporating characterized plant-growth-promoting bacteria or fungal strains into compost derived from agricultural waste, offer a promising solution. These biofertilizers, with selected microbial strains capable of thriving in compost, offer an eco-friendly, cost-effective, and sustainable alternative for agricultural practices. In this review article, we explore the potential of microbial composts as a viable strategy for improving plant growth and environmental safety. By harnessing the benefits of microorganisms in compost, we can pave the way for sustainable agriculture and foster a healthier relationship between soil, plants, and the environment.

Microbial Exudates as Biostimulants: Role in Plant Growth Promotion and Stress Mitigation

Microbes hold immense potential, based on the fact that they are widely acknowledged for their role in mitigating the detrimental impacts of chemical fertilizers and pesticides, which were extensively employed during the Green Revolution era. The consequence of this extensive use has been the degradation of agricultural land, soil health and fertility deterioration, and a decline in crop quality. Despite the existence of environmentally friendly and sustainable alternatives, microbial bioinoculants encounter numerous challenges in real-world agricultural settings. These challenges include harsh environmental conditions like unfavorable soil pH, temperature extremes, and nutrient imbalances, as well as stiff competition with native microbial species and host plant specificity. Moreover, obstacles spanning from large-scale production to commercialization persist. Therefore, substantial efforts are underway to identify superior solutions that can foster a sustainable and eco-conscious agricultural system. In this context, attention has shifted towards the utilization of cell-free microbial exudates as opposed to traditional microbial inoculants. Microbial exudates refer to the diverse array of cellular metabolites secreted by microbial cells. These metabolites enclose a wide range of chemical compounds, including sugars, organic acids, amino acids, peptides, siderophores, volatiles, and more. The composition and function of these compounds in exudates can vary considerably, depending on the specific microbial strains and prevailing environmental conditions. Remarkably, they possess the capability to modulate and influence various plant physiological processes, thereby inducing tolerance to both biotic and abiotic stresses. Furthermore, these exudates facilitate plant growth and aid in the remediation of environmental pollutants such as chemicals and heavy metals in agroecosystems. Much like live microbes, when applied, these exudates actively participate in the phyllosphere and rhizosphere, engaging in continuous interactions with plants and plant-associated microbes. Consequently, they play a pivotal role in reshaping the microbiome. The biostimulant properties exhibited by these exudates position them as promising biological components for fostering cleaner and more sustainable agricultural systems.

Fungal volatiles have physiological properties

All fungi emit mixtures of volatile organic compounds (VOCs) during growth. The qualitative and quantitative composition of these volatile mixtures vary with the species of fungus, the age of the fungus, and the environmental parameters attending growth. In nature, fungal VOCs are found as combinations of alcohols, aldehydes, acids, ethers, esters, ketones, terpenes, thiols and their derivatives, and are responsible for the characteristic odors associated with molds, mushrooms and yeasts. One of the single most common fungal volatiles is 1-octen-3-ol also known as "mushroom alcohol" or "matsutake alcohol." Many volatiles, including 1-octen-3-ol, serve as communication agents and display biological activity as germination inhibitors, plant growth retardants or promoters, and as semiochemicals ("infochemicals") in interactions with arthropods. Volatiles are understudied and underappreciated elements of the chemical lives of fungi. This review gives a brief introduction to fungal volatiles in hopes of raising awareness of the physiological importance of these gas phase fungal metabolites to encourage mycologists and other biologists to stop "throwing away the head space."

Biocontrol potential of endophytic fungi originated from grapevine leaves for management of anthracnose disease caused by Colletotrichum gloeosporioides

In the present study, 51 fungal endophytes (FEs) were isolated, purified and identified from the healthy leaf segments of ten grapevine varieties based on the spore and colony morphologies and ITS sequence information. The FEs belonged to the Ascomycota division comprising eight genera viz., Alternaria, Aspergillus, Bipolaris, Curvularia, Daldinia, Exserohilum, Fusarium and Nigrospora. The in vitro direct confrontation assay against Colletotrichum gloeosporioides revealed that six isolates viz., VR8 (70%), SB2 (83.15%), CS2 (88.42%), MN3 (88.42%), MS5 (78.94%) and MS15 (78.94%) inhibited the mycelial growth of test pathogen. The remaining 45 fungal isolates showed 20-59.9% growth inhibition of C. gloeosporioides. Indirect confrontation assay manifested that the isolates MN1 and MN4a showed 79.09% and 78.18% growth inhibition of C. gloeosporioides followed by MM4 (73.63%) and S5 (71.81%) isolates. Isolate S5 and MM4 were found to produce azulene and 1,3-Cyclopentanedione, 4,4-dimethyl as antimicrobial volatile organic compounds, respectively. The 38 FEs showed PCR amplification using internal transcribed spacer universal primers. The BLAST search revealed highest similarity with the existing sequences in the database. The phylogenetic analysis revealed the occurrence of seven distinct clusters each corresponding to single genus.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03675-z.

Chitosan Modulates Volatile Organic Compound Emission from the Biocontrol Fungus Pochonia chlamydosporia

Fungal volatile organic compounds (VOCs) are responsible for fungal odor and play a key role in biological processes and ecological interactions. VOCs represent a promising area of research to find natural metabolites for human exploitation. Pochonia chlamydosporia is a chitosan-resistant nematophagous fungus used in agriculture to control plant pathogens and widely studied in combination with chitosan. The effect of chitosan on the production of VOCs from P. chlamydosporia was analyzed using gas chromatography-mass spectrometry (GC-MS). Several growth stages in rice culture medium and different times of exposure to chitosan in modified Czapek-Dox broth cultures were analyzed. GC-MS analysis resulted in the tentative identification of 25 VOCs in the rice experiment and 19 VOCs in the Czapek-Dox broth cultures. The presence of chitosan in at least one of the experimental conditions resulted in the de novo production of 3-methylbutanoic acid and methyl 2,4-dimethylhexanoate, and oct-1-en-3-ol and tetradec-1-ene in the rice and Czapek-Dox experiments, respectively. Other VOCs changed their abundance because of the effect of chitosan and fungal age. Our findings suggest that chitosan can be used as a modulator of the production of VOCs in P. chlamydosporia and that there is also an effect of fungal age and exposure time.

Integrative analysis of genomic and metabolomic data reveals key metabolic pathways involved in lipid and carotenoid biosynthesis in oleaginous red yeast Rhodosporidiobolus odoratus XQR

Rhodosporidiobolus odoratus, one of the oleaginous red yeasts, is gaining biotechnological importance for their ability to produce microbial lipids and carotenoids. However, to date, the genomic resource underling lipid and carotenoid biosynthesis in R. odoratus has not been reported. Here, we reported the first genome assembly of R. odoratus using a combination of PacBio and Illumina techniques. The final genome assembly is 23.74 Mb in size, containing 52 scaffolds with a N50 length of 1200,460 bp and a GC content of 56.90%. Benchmarking Universal Single-Copy Orthologs (BUSCO) assessment showed that our assembly contains 94.23% of Basidiomycota universal single-copy orthologs. The genome was predicted to contain 4986 protein-coding genes, 4967 of which were functionally annotated. Metabolomic profiling identified 574 lipids, 3 carotenoids, and 208 volatile organic compounds synthesized by R. odoratus. Integrative analysis of genomics and metabolomics provides insights into the biosynthesis of lipid, carotenoid, and other bioactive compounds in R. odoratus. Collectively, the results presented herein greatly enhance our understanding of R. odoratus in lipids and carotenoids biosynthesis, and thus further accelerate its fundamental molecular investigations and biotechnological applications.

Toward the Analysis of Volatile Organic Compounds from Tomato Plants (Solanum lycopersicum L.) Treated with Trichoderma virens or/and Botrytis cinerea

Gray mold caused by Botrytis cinerea causes significant losses in tomato crops. B. cinerea infection may be halted by volatile organic compounds (VOCs), which may exhibit fungistatic activity or enhance the defense responses of plants against the pathogen. The enhanced VOC generation was observed in tomato (Solanum lycopersicum L.), with the soil-applied biocontrol agent Trichoderma virens (10⁶ spores/1 g soil), which decreased the gray mold disease index in plant leaves at 72 hpi with B. cinerea suspension (1 × 10⁶ spores/mL). The tomato leaves were found to emit 100 VOCs, annotated and putatively annotated, assigned to six classes by the headspace GCxGC TOF-MS method. In Trichoderma-treated plants with a decreased grey mold disease index, the increased emission or appearance of 2-hexenal, (2E,4E)-2,4-hexadienal, 2-hexyn-1-ol, 3,6,6-trimethyl-2-cyclohexen-1-one, 1-octen-3-ol, 1,5-octadien-3-ol, 2-octenal, octanal, 2-penten-1-ol, (Z)-6-nonenal, prenol, and acetophenone, and 2-hydroxyacetophenone, β-phellandrene, β-myrcene, 2-carene, δ-elemene, and isocaryophyllene, and β-ionone, 2-methyltetrahydrofuran, and 2-ethyl-, and 2-pentylfuran, ethyl, butyl, and hexyl acetate were most noticeable. This is the first report of the VOCs that were released by tomato plants treated with Trichoderma, which may be used in practice against B. cinerea, although this requires further analysis, including the complete identification of VOCs and determination of their potential as agents that are capable of the direct and indirect control of pathogens.

The Exploitation of Microbial Antagonists against Postharvest Plant Pathogens

Postharvest disease management is vital to increase the quality and productivity of crops. As part of crop disease protection, people used different agrochemicals and agricultural practices to manage postharvest diseases. However, the widespread use of agrochemicals in pest and disease control has detrimental effects on consumer health, the environment, and fruit quality. To date, different approaches are being used to manage postharvest diseases. The use of microorganisms to control postharvest disease is becoming an eco-friendly and environmentally sounds approach. There are many known and reported biocontrol agents, including bacteria, fungi, and actinomycetes. Nevertheless, despite the abundance of publications on biocontrol agents, the use of biocontrol in sustainable agriculture requires substantial research, effective adoption, and comprehension of the interactions between plants, pathogens, and the environment. To accomplish this, this review made an effort to locate and summarize earlier publications on the function of microbial biocontrol agents against postharvest crop diseases. Additionally, this review aims to investigate biocontrol mechanisms, their modes of operation, potential future applications for bioagents, as well as difficulties encountered during the commercialization process.

Chemical Characterization of Trichoderma spp. Extracts with Antifungal Activity against Cocoa Pathogens

Ecuador is one of the major cocoa producers worldwide, but its productivity has lately been affected by diseases. Endophytic biocontrol agents have been used to minimize pathogenic effects; however, compounds produced by endophytes are minimally understood. This work presents the chemical characterization of the Trichoderma species extracts that proved inhibition against cocoa pathogens. Solid-liquid extraction was performed as a partitioning method using medium with the fungal mycelia of Trichoderma reesei (C2A), Trichoderma sp. (C3A), Trichoderma harzianum (C4A), and Trichoderma spirale (C10) in ethyl acetate individually. The extract of T. spirale (C10) exhibited the growth inhibition (32.97-47.02%) of Moniliophthora perniciosa at 10 µg/mL, while a slight stimulation of Moniliophthora roreri was shown by the extracts of T. reesei (C2A) and T. harzianum (C4A) at higher concentrations. The inhibitory activity could be related to alkaloids, lactones, quinones, flavonoids, triterpenes, and sterols, as indicated by chemical screening and antifungal compounds, such as widdrol, β-caryophyllene, tyrosol, butyl isobutyrate, sorbic acid, palmitic acid, palmitelaidic acid, linoleic acid, and oleic acid, which were identified by gas chromatography-mass spectrometry (GC-MS). The results showed that the extracts, particularly T. spirale (C10), have the potential as biocontrol agents against witches' broom disease; however, further studies are needed to confirm their effectiveness.

Volatile Organic Compounds: A Promising Tool for Bed Bug Detection

The recent decades' resurgence of bed bugs as a public health concern in industrialized countries has driven an increased interest on new sustainable insecticide-free methods to monitor and control these ectoparasites. Current methods of detection rely mainly on visual inspection or canine scent detection, which are methods that are time-consuming, require experience, are non-specific or require costly mission repetitions. Volatile organic compounds (VOCs) are considered an environmentally friendly alternative and a promising approach for bed bug detection. An overview of the released literature on VOCs, their chemical characteristics and their role in bed bugs' intra- and inter-species communications allowed us to highlight the identification of 49 VOCs in Cimex lectularius (23 molecules) and C. hemipterus (26), which are emitted by both sexes during diverse compartments including aggregation (46), mating (11), defense (4), etc., and all life stages including exuviae or dead bed bugs as a principal indicator of infestation. The latter has a great importance for application of these semiochemicals in successful detection and control management of bed bugs and to prevent their further dispersion. This approach has the advantage of more reliability compared to conventional detection methods with no need for repeated inspections, household furniture moving or resident rehousing for bed bugs' VOC detection, which are commonly performed by active or passive sampling with absorbing tubes and analyzed by gas chromatography-based analytical platforms.

Deciphering the antimicrobial activity of multifaceted rhizospheric biocontrol agents of solanaceous crops viz., Trichoderma harzianum MC2, and Trichoderma harzianum NBG

The Solanaceae family is generally known to be the third most economically important plant taxon, but also harbors a host of plant pathogens. Diseases like wilt and fruit rot of solanaceous crops cause huge yield losses in the field as well as in storage. In the present study, eight isolates of Trichoderma spp. were obtained from rhizospheric micro-flora of three solanaceous crops: tomato, brinjal, and chili plants, and were subsequently screened for pre-eminent biocontrol activity against three fungal (Fusarium oxysporum f. sp. lycopersicum, Colletotrichum gloeosporioides, and Rhizoctonia solani) and one bacterial (Ralstonia solanacearum) pathogen. Morphological, ITS, and tef1α marker-based molecular identification revealed eight isolates were different strains of Trichoderma. Seven isolates were distinguished as T. harzianum while one was identified as T. asperellum. In vitro antagonistic and biochemical assays indicated significant biocontrol activity governed by all eight isolates. Two fungal isolates, T. harzianum MC2 and T. harzianum NBG were further evaluated to decipher their best biological control activity. Preliminary insights into the secondary metabolic profile of both isolates were retrieved by liquid chromatography-mass spectrometry (LC-MS). Further, a field experiment was conducted with the isolates T. harzianum MC2 and T. harzianum NBG which successfully resulted in suppression of bacterial wilt disease in tomato. Which possibly confer biocontrol properties to the identified isolates. The efficacy of these two strains in suppressing bacterial wilt and promoting plant growth in the tomato crop was also tested in the field. The disease incidence was significantly reduced by 47.50% and yield incremented by 54.49% in plants treated in combination with both the bioagents. The results of scanning electron microscopy were also in consensus with the in planta results. The results altogether prove that T. harzianum MC2 and T. harzianum NBG are promising microbes for their prospective use in agricultural biopesticide formulations.

Endophytic species of Induratia from coffee and carqueja plants from Brazil and its potential for the biological control of toxicogenic fungi on coffee beans by means of antimicrobial volatiles

Several endophytic fungi have been reported to have produced bioactive metabolites. Some of them, including the Induratia species, have the capacity to emit volatile compounds with antimicrobial properties with broad spectrum against human and plant pathogens. The present study aimed to prospect the Induratia species producing volatile organic compounds (VOCs), in carqueja plants used in alternative medicine and coffee plants in Brazil. A total of 11 fungal isolates producing volatile metabolites were obtained by a parallel growth technique, using I. alba 620 as a reference strain. Phylogenetic relationships revealed the presence of at least three distinct species, I. coffeana, I. yucatanensis, and Induratia sp. SPME/GC/MS analyses of the VOCs in the headspace above the mycelium from Induratia species cultured for 10 days on PDA revealed the volatile profile emitted by I. coffeana CCF 572, I. coffeana COAD 2055, I. yucatanensis COAD 2062, and Induratia sp. COAD 2059. Volatile organic compounds produced by I. coffeana isolates presented antimicrobial activity against Aspergillus ochraceus, A. sclerotiorum, A. elegans, A. foetidus, A. flavus, A. tamari, A. tubingensis, A. sydowii, A. niger, A. caespitosus, A. versicolor, and A. expansum, sometimes by decreasing the growth rate or, mainly, by fully inhibiting colony growth. Fifty-eight percent of the target species died after 6 days of exposure to VOCs emitted by I. coffeana CCF 572. In addition, VOCs emitted by the same fungus inhibited the growth in A. ochraceus inoculated into coffee beans, which indicates that plants which have I. coffeana as an endophyte may be protected from attacks by this plant pathogen.

Volatile Organic Compounds from Pythium oligandrum Play a Role in Its Parasitism on Plant-Pathogenic Pythium myriotylum

The oomycete Pythium oligandrum is a soil-inhabiting parasite and predator of both fungi and oomycetes, and uses hydrolytic enzymes extensively to penetrate and hydrolyze its host or prey. Other mechanisms have been studied less, and we investigated the contribution of P. oligandrum-produced volatile organic compounds (VOCs) to parasitism. The growth-inhibiting activity of P. oligandrum VOCs was tested on Pythium myriotylum-a host or prey of P. oligandrum-coupled with electron microscopy, and biochemical and transcriptomic analyses. The P. oligandrum-produced VOCs reduced P. myriotylum growth by 80% and zoospore levels by 60%. Gas chromatography-mass spectrometry (GC-MS) identified 23 VOCs, and methyl heptenone, d-limonene, 2-undecanone, and 1-octanal were potent inhibitors of P. myriotylum growth and led to increased production of reactive oxygen species at a concentration that did not inhibit P. oligandrum growth. Exposure to the P. oligandrum VOCs led to shrinkage of P. myriotylum hyphae and lysis of the cellular membranes and organelles. Transcriptomics of P. myriotylum exposed to the P. oligandrum VOCs at increasing levels of growth inhibition initially showed a strong upregulation of putative detoxification-related genes that was not maintained later. The inhibition of P. myriotylum growth continued immediately after the exposure to the VOCs was discontinued and led to the reduced infection of its plant hosts. The VOCs produced by P. oligandrum could be another factor alongside hydrolytic enzymes contributing to its ecological role as a microbial parasite in particular ecological niches such as in soil, and may also contribute to the biocontrol of diseases using P. oligandrum commercial preparations. IMPORTANCE Microbe-microbe interactions in nature are multifaceted, with multiple mechanisms of action, and are crucial to how plants interact with microbes. Volatile organic compounds (VOCs) have diverse functions, including contributing to parasitism in ecological interactions and potential applications in biocontrol. The microbial parasite P. oligandrum is well known for using hydrolytic enzymes as part of its parasitism. We found that P. oligandrum VOCs reduced the growth of, and caused major damage to, the hyphae of P. myriotylum (a host or prey of P. oligandrum). Transcriptomic analyses of P. myriotylum exposed to the VOCs revealed the upregulation of genes potentially involved in an attempt to detoxify the VOCs. The inhibitory effects of the VOCs had a knock-on effect by reducing the virulence of P. myriotylum toward its plant hosts. The P. oligandrum VOCs could contribute to its ecological role as a microbial parasite. The VOCs analyzed here may also contribute to the biocontrol of diseases using P. oligandrum commercial preparations.

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.

E-Nose Technology for Mycotoxin Detection in Feed: Ready for a Real Context in Field Application or Still an Emerging Technology?

Mycotoxin risk in the feed supply chain poses a concern to animal and human health, economy, and international trade of agri-food commodities. Mycotoxin contamination in feed and food is unavoidable and unpredictable. Therefore, monitoring and control are the critical points. Effective and rapid methods for mycotoxin detection, at the levels set by the regulations, are needed for an efficient mycotoxin management. This review provides an overview of the use of the electronic nose (e-nose) as an effective tool for rapid mycotoxin detection and management of the mycotoxin risk at feed business level. E-nose has a high discrimination accuracy between non-contaminated and single-mycotoxin-contaminated grain. However, the predictive accuracy of e-nose is still limited and unsuitable for in-field application, where mycotoxin co-contamination occurs. Further research needs to be focused on the sensor materials, data analysis, pattern recognition systems, and a better understanding of the needs of the feed industry for a safety and quality management of the feed supply chain. A universal e-nose for mycotoxin detection is not realistic; a unique e-nose must be designed for each specific application. Robust and suitable e-nose method and advancements in signal processing algorithms must be validated for specific needs.

Volatile compounds for biotechnological applications produced during competitive interactions between yeasts and fungi

Fungi, yeasts and bacteria produce volatile compounds during their metabolism. In this study, the volatile compounds produced by yeast strains (Saccharomyces cerevisiae and Rhodotorula mucilaginosa) and fungal strains (Aspergillus carbonarius and Aspergillus ochraceus) during competitive interactions were investigated by solid-phase microextraction coupled with gas chromatography-mass spectrometry. Fifty-six volatile compounds were identified representing alcohols, aldehydes, esters, ketones, aromatic compounds, acids, furans, phenols, and nitrogen compounds, being the largest amount in the class of esters and alcohols. Eight compounds were identified only in interactive culture conditions such as 2-amino-1-propanol, isopropylamine, dimethylamine, pentyl propanoate, ethyl-2-aminopropanoate, acetone, oxalic acid, and β-elemene and five of these were produced in cocultures including A. carbonarius. These will be developed for future biotechnological applications such as in the pharmaceutical and biological industry to produce drugs. Antimicrobial and antifungal activities; Solvent and herbicide; flavoring ingredient; solvent, plastic synthesis, nail polish remover and thinner, pesticide and herbicide; important in the complexation of minerals in the soil; and plant-environment interactions, defending predators, pathogens, and competitors.

Application of Ceriporia lacerata HG2011 as biocontrol agent against multiple phytopathogenic fungi and oomycetes

Overuse of fungicides to control crop diseases results in ecological damage, environmental pollution, and human health risks. Biocontrol is an increasingly popular alternative in plant disease management due to sustainability and environmental friendliness. Herein, antagonistic tests and greenhouse experiments were conducted to investigate the antagonism of a self-isolated white-rot fungus Ceriporia lacerata HG2011 against phytopathogens in vitro, the underlying mechanism exerted by this fungus, and disease control efficiency in the greenhouse. The results demonstrated that both soluble and volatile substances produced by this fungus suppressed the growth of all test phytopathogen fungi and oomycetes in vitro, with the inhibitory rates of 10.4-60.6% for soluble metabolites and 30.3-52.9% for volatiles. C. lacerata HG2011 could grow in and gradually spread on living phytopathogenic colonies, concurrently deformed and lysed pathogenic hyphae in dual culture, which were associated with the release of hydrolase (cellulose, chitinase, β-glucanase, and protease) from this biocontrol fungus for the use of the pathogens as nutrient sources. The chitinolytic and cellulolytic production by C. lacerata HG2011 presents the specific response to the cell wall of pathogenic fungi and oomycetes, and β-glucanase was triggered by carbon competition. Consequently, C. lacerata HG2011 successfully controlled eggplant stem blight and cucumber vine blight (control efficacy 67.9-70.9%) in the greenhouse experiments. C. lacerata HG2011 showed multiple antagonistic mechanisms against the phytopathogenic fungi and oomycetes concurrently. Our results provided information about a new potential use of this fungus as a biocontrol agent to control plant diseases in modern agriculture beyond medical purposes, wastewater treatment, and biofuel production.

Perfume Guns: Potential of Yeast Volatile Organic Compounds in the Biological Control of Mycotoxin-Producing Fungi

Pathogenic fungi in the genera Alternaria, Aspergillus, Botrytis, Fusarium, Geotrichum, Gloeosporium, Monilinia, Mucor, Penicillium, and Rhizopus are the most common cause of pre- and postharvest diseases of fruit, vegetable, root and grain commodities. Some species are also able to produce mycotoxins, secondary metabolites having toxic effects on human and non-human animals upon ingestion of contaminated food and feed. Synthetic fungicides still represent the most common tool to control these pathogens. However, long-term application of fungicides has led to unacceptable pollution and may favour the selection of fungicide-resistant mutants. Microbial biocontrol agents may reduce the incidence of toxigenic fungi through a wide array of mechanisms, including competition for the ecological niche, antibiosis, mycoparasitism, and the induction of resistance in the host plant tissues. In recent years, the emission of volatile organic compounds (VOCs) has been proposed as a key mechanism of biocontrol. Their bioactivity and the absence of residues make the use of microbial VOCs a sustainable and effective alternative to synthetic fungicides in the management of postharvest pathogens, particularly in airtight environments. In this review, we will focus on the possibility of applying yeast VOCs in the biocontrol of mycotoxigenic fungi affecting stored food and feed.

The Health and Clinical Benefits of Medicinal Fungi

The human uses of mushrooms and cultured mycelium products for nutrition and medicine are detailed and supported by available human studies, which in many cases are clinical trials published in peer-reviewed journals. The major medically active immunomodulating compounds in the cell walls-chitin, beta-glucans, and glycoproteins, as well as lower weight molecules-nitrogen-containing compounds, phenolics, and terpenes-are discussed in relation to their current clinical uses. The nutritional content and foods derived from mushrooms, particularly related to their medical benefits, are discussed. High-quality major nutrients such as the high amounts of complete protein and prebiotic fibers found in edible and medicinal fungi and their products are presented. Mushrooms contain the highest amount of valuable medicinal fiber, while dried fruiting bodies of some fungi have up to 80% prebiotic fiber. These fibers are particularly complex and are not broken down in the upper gut, so they can diversify the microbiome and increase the most beneficial species, leading to better immune regulation and increasing normalizing levels of crucial neurotransmitters like serotonin and dopamine. Since the growth of medicinal mushroom products is expanding rapidly worldwide, attention is placed on reviewing important aspects of mushroom and mycelium cultivation and quality issues relating to adulteration, substitution, and purity and for maximizing medicinal potency. Common questions surrounding medicinal mushroom products in the marketplace, particularly the healing potential of fungal mycelium compared with fruiting bodies, extraction methods, and the use of fillers in products, are all explored, and many points are supported by the literature.

Antagonism of volatile organic compounds of the Bacillus sp. against Fusarium kalimantanense

Fusarium kalimantanense is a genetic lineage of Fusarium oxysporum f. sp. cubense (Foc) and belongs to the Fusarium oxysporum species complex (FOSC). This pathogen is a causative agent of Panama disease, an infection that has caused damage to the banana crop worldwide. Bacillus sp. (LPPC170) showed preliminary antagonist activity against F. kalimantanense (LPPC130) in vitro tests from the cultivation of axenic culture and co-culture with inhibition of mycelial growth of phytopathogen of 41.23%. According to these findings, volatile organic compounds (VOCs) emitted from Bacillus sp. were obtained by solid-phase microextraction and identified by gas chromatography coupled with a mass spectrometer (GC-MS). The multivariate data analysis tool (PLS-DA and Heatmap) identified short-chain organic acids as the main antagonistic VOCs responsible for inhibiting the mycelial growth of LPPC130. Acetic acid, propanoic acid, butanoic acid, valeric acid, and isovaleric acid exhibited a strong inhibitory effect on the mycelial growth of LPPC130, with inhibition of 20.68%, 33.30%, 26.87%, 43.71%, and 53.10%, respectively. Scanning electron microscopy revealed that VOCs caused damage to the vegetative and reproductive structures of the fungus. These results suggest Bacillus LPPC170 as an excellent biocontrol tool against the phytopathogen causative agents of Panama disease.

Utilizing volatile organic compounds for early detection of Fusarium circinatum

Fusarium circinatum, a fungal pathogen deadly to many Pinus species, can cause significant economic and ecological losses, especially if it were to become more widely established in Europe. Early detection tools with high-throughput capacity can increase our readiness to implement mitigation actions against new incursions. This study sought to develop a disease detection method based on volatile organic compound (VOC) emissions to detect F. circinatum on different Pinus species. The complete pipeline applied here, entailing gas chromatography-mass spectrometry of VOCs, automated data analysis and machine learning, distinguished diseased from healthy seedlings of Pinus sylvestris and Pinus radiata. In P. radiata, this distinction was possible even before the seedlings became visibly symptomatic, suggesting the possibility for this method to identify latently infected, yet healthy looking plants. Pinus pinea, which is known to be relatively resistant to F. circinatum, remained asymptomatic and showed no changes in VOCs over 28 days. In a separate analysis of in vitro VOCs collected from different species of Fusarium, we showed that even closely related Fusarium spp. can be readily distinguished based on their VOC profiles. The results further substantiate the potential for volatilomics to be used for early disease detection and diagnostic recognition.

Weapons against Themselves: Identification and Use of Quorum Sensing Volatile Molecules to Control Plant Pathogenic Fungi Growth

Quorum sensing (QS) is often defined as a mechanism of microbial communication that can regulate microbial behaviors in accordance with population density. Much is known about QS mechanisms in bacteria, but fungal QS research is still in its infancy. In this study, the molecules constituting the volatolomes of the plant pathogenic fungi Fusarium culmorum and Cochliobolus sativus have been identified during culture conditions involving low and high spore concentrations, with the high concentration imitating overpopulation conditions (for QS stimulation). We determined that volatolomes emitted by these species in conditions of overpopulation have a negative impact on their mycelial growth, with some of the emitted molecules possibly acting as QSM. Candidate VOCs related to QS have then been identified by testing the effect of individual volatile organic compounds (VOCs) on mycelial growth of their emitting species. The antifungal effect observed for the volatolome of F. culmorum in the overpopulation condition could be attributed to ethyl acetate, 2-methylpropan-1-ol, 3-methylbutyl ethanoate, 3-methylbutan-1-ol, and pentan-1-ol, while it could be attributed to longifolene, 3-methylbutan-1-ol, 2-methylpropan-1-ol, and ethyl acetate for C. sativus in the overpopulation condition. This work could pave the way to a sustainable alternative to chemical fungicides.

Impact of Volatile Organic Compounds on the Growth of Aspergillus flavus and Related Aflatoxin B1 Production: A Review

Volatile organic compounds (VOCs) are secondary metabolites of varied chemical nature that are emitted by living beings and participate in their interactions. In addition, some VOCs called bioactive VOCs cause changes in the metabolism of other living species that share the same environment. In recent years, knowledge on VOCs emitted by Aspergillus flavus, the main species producing aflatoxin B1 (AFB1), a highly harmful mycotoxin, has increased. This review presents an overview of all VOCs identified as a result of A. flavus toxigenic (AFB1-producing) and non-toxigenic (non AFB1-producing) strains growth on different substrates, and the factors influencing their emissions. We also included all bioactive VOCs, mixes of VOCs or volatolomes of microbial species that impact A. flavus growth and/or related AFB1 production. The modes of action of VOCs impacting the fungus development are presented. Finally, the potential applications of VOCs as biocontrol agents in the context of mycotoxin control are discussed.

Volatile organic compounds shape belowground plant-fungi interactions

Volatile organic compounds (VOCs), a bouquet of chemical compounds released by all life forms, play essential roles in trophic interactions. VOCs can facilitate a large number of interactions with different organisms belowground. VOCs-regulated plant-plant or plant-insect interaction both below and aboveground has been reported extensively. Nevertheless, there is little information about the role of VOCs derived from soilborne pathogenic fungi and beneficial fungi, particularly mycorrhizae, in influencing plant performance. In this review, we show how plant VOCs regulate plant-soilborne pathogenic fungi and beneficial fungi (mycorrhizae) interactions. How fungal VOCs mediate plant-soilborne pathogenic and beneficial fungi interactions are presented and the most common methods to collect and analyze belowground volatiles are evaluated. Furthermore, we suggest a promising method for future research on belowground VOCs.

Insect-Microorganism Interaction Has Implicates on Insect Olfactory Systems

Olfaction plays an essential role in various insect behaviors, including habitat selection, access to food, avoidance of predators, inter-species communication, aggregation, and reproduction. The olfactory process involves integrating multiple signals from external conditions and internal physiological states, including living environments, age, physiological conditions, and circadian rhythms. As microorganisms and insects form tight interactions, the behaviors of insects are constantly challenged by versatile microorganisms via olfactory cues. To better understand the microbial influences on insect behaviors via olfactory cues, this paper summarizes three different ways in which microorganisms modulate insect behaviors. Here, we deciphered three interesting aspects of microorganisms-contributed olfaction: (1) How do volatiles emitted by microorganisms affect the behaviors of insects? (2) How do microorganisms reshape the behaviors of insects by inducing changes in the synthesis of host volatiles? (3) How do symbiotic microorganisms act on insects by modulating behaviors?

Differential Expression of Genes Related to Growth and Aflatoxin Synthesis in Aspergillus flavus When Inhibited by Bacillus velezensis Strain B2

Aspergillus flavus is a saprophytic soil fungus that infects and contaminates seed crops with the highly carcinogenic aflatoxin, which brings health hazards to animals and humans. In this study, bacterial strains B1 and B2 isolated from the rhizosphere soil of camellia sinensis had significant antagonistic activities against A. flavus. Based on the phylogenetic analysis of 16SrDNA gene sequence, bacterial strains B1 and B2 were identified as Bacillus tequilensis and Bacillus velezensis, respectively. In addition, the transcriptome analysis showed that some genes related to A. flavus growth and aflatoxin synthesis were differential expressed and 16 genes in the aflatoxin synthesis gene cluster showed down-regulation trends when inhibited by Bacillus velezensis strain B2. We guessed that the Bacillus velezensis strain B2 may secrete some secondary metabolites, which regulate the related gene transcription of A. flavus to inhibit growth and aflatoxin production. In summary, this work provided the foundation for the more effective biocontrol of A. flavus infection and aflatoxin contamination by the determination of differential expression of genes related to growth and aflatoxin synthesis in A. flavus when inhibited by B. velezensis strain B2.

Fungal exposome, human health, and unmet needs: A 2022 update with special focus on allergy

Humans inhale, ingest, and touch thousands of fungi each day. The ubiquity and diversity of the fungal kingdom, reflected by its complex taxonomy, are in sharp contrast with our scarce knowledge about its distribution, pathogenic effects, and effective interventions at the environmental and individual levels. Here, we present an overview of salient features of fungi as permanent players of the human exposome and key determinants of human health, through the lens of fungal allergy and other fungal hypersensitivity reactions. Improved understanding of the fungal exposome sheds new light on the epidemiology of fungal-related hypersensitivity diseases, their immunological substratum, the currently available methods, and biomarkers for environmental and medical fungi. Unmet needs are described and potential approaches are highlighted as perspectives.

Variability in metabolites produced by Talaromyces pinophilus SPJ22 cultured on different substrates

BACKGROUND

Several metabolites released by fungal species are an essential source of biologically active natural substances. Gas chromatography high resolution time-of-flight mass spectrometry (GC-HRTOF-MS) is one of the techniques used in profiling the metabolites produced by microorganisms, including Talaromyces pinophilus. However, there is limited information regarding differential substrates' impacts on this fungal strain's metabolite profiling. This study examined the metabolite profile of T. pinophilus strain SPJ22 cultured on three different media, including solid czapek yeast extract agar (CYA), malt extract agar (MEA) and potato dextrose agar (PDA) using GC-HRTOF-MS. The mycelia including the media were plugged and dissolved in 5 different organic solvents with varying polarities viz.: acetonitrile, dichloromethane, hexane, 80% methanol and water, and extracts analysed on GC-HRTOF-MS.

RESULTS

The study revealed the presence of different classes of metabolites, such as fatty acids (2.13%), amides (4.26%), alkanes (34.04%), furan (2.13%), ketones (4.26%), alcohols (14.89%), aromatic compounds (6.38%), and other miscellaneous compounds (17.02%). Significant metabolites such as acetic acid, 9-octadecenamide, undecanoic acid methyl ester, hydrazine, hexadecane, nonadecane, eicosane, and other compounds reported in this study have been widely documented to have plant growth promoting, antimicrobial, anti-inflammatory, antioxidant, and biofuel properties. Furthermore, T. pinophilus grown on PDA and MEA produced more than twice as many compounds as that grown on CYA.

CONCLUSION

Thus, our result showed that the production of essential metabolites from T. pinophilus is substrate dependent, with many of these metabolites known to have beneficial characteristics, and as such, this organism can be utilised as a sustainable and natural source for these useful organic molecules.

Autotoxicity of Endogenous Organic Acid Stress in Two Ganoderma lucidum Cultivars

Ganoderma lucidum has been used as a rare medical mushroom for centuries in China, due to its health-promoting properties. Successive cropping obstacles are common in the cultivation of G. lucidum, although the remaining nutrients in the germ substrate are sufficient for a second fruiting. Here, we aimed to study the metabolite profile of G. lucidum via nontargeted metabonomic technology. Metabonomic data revealed that organic acids played an important role in the cropping obstacles of G. lucidum, which is accordance with the pH decrease in the germ substrate. A Kyoto encyclopedia of genes and genomes (KEGG) enrichment analysis indicated that most differential acids participated in the metabolic pathways. Five acids were all significantly upregulated by two MS with high energy (MSE) modes in two cultivars, among which 5-hydroxy-2-oxo-4-ureido-2,5-dihydro-1H-imidazole-5-carboxylic acid is also involved in purine metabolism regulation and microbial metabolism in diverse environments. Taken together, this work illustrated the organic acid stress generated by G. lucidum, which formed the autotoxicity feedback, and resulted in cropping obstacles. Determining the cause of the cropping obstacles in G. lucidum will promote the utilization rate of fungus substrate to realize the sustainable use of this resource.

Volatile Organic Compound (VOC) Profiles of Different Trichoderma Species and Their Potential Application

Fungi emit a broad spectrum of volatile organic compounds (VOCs), sometimes producing species-specific volatile profiles. Volatilomes have received over the last decade increasing attention in ecological, environmental and agricultural studies due to their potential to be used in the biocontrol of plant pathogens and pests and as plant growth-promoting factors. In the present study, we characterised and compared the volatilomes from four different Trichoderma species: T. asperellum B6; T. atroviride P1; T. afroharzianum T22; and T. longibrachiatum MK1. VOCs were collected from each strain grown both on PDA and in soil and analysed using proton transfer reaction quadrupole interface time-of-flight mass spectrometry (PTR-Qi-TOF-MS). Analysis of the detected volatiles highlighted a clear separation of the volatilomes of all the four species grown on PDA whereas the volatilomes of the soil-grown fungi could be only partially separated. Moreover, a limited number of species-specific peaks were found and putatively identified. In particular, each of the four Trichoderma species over-emitted somevolatiles involved in resistance induction, promotion of plant seed germination and seedling development and antimicrobial activity, as 2-pentyl-furan, 6PP, acetophenone and p-cymene by T. asperellum B6, T. atroviride P1, T. afroharzianum T22 and T. longibrachiatum MK1, respectively. Their potential role in interspecific interactions from the perspective of biological control is briefly discussed.

Mapping the human gut mycobiome in middle-aged and elderly adults: multiomics insights and implications for host metabolic health

OBJECTIVE

The human gut fungal community, known as the mycobiome, plays a fundamental role in the gut ecosystem and health. Here we aimed to investigate the determinants and long-term stability of gut mycobiome among middle-aged and elderly adults. We further explored the interplay between gut fungi and bacteria on metabolic health.

DESIGN

The present study included 1244 participants from the Guangzhou Nutrition and Health Study. We characterised the long-term stability and determinants of the human gut mycobiome, especially long-term habitual dietary consumption. The comprehensive multiomics analyses were performed to investigate the ecological links between gut bacteria, fungi and faecal metabolome. Finally, we examined whether the interaction between gut bacteria and fungi could modulate the metabolic risk.

RESULTS

The gut fungal composition was temporally stable and mainly determined by age, long-term habitual diet and host physiological states. Specifically, compared with middle-aged individuals, Blastobotrys and Agaricomycetes spp were depleted, while Malassezia was enriched in the elderly. Dairy consumption was positively associated with Saccharomyces but inversely associated with Candida. Notably, Saccharomycetales spp interacted with gut bacterial diversity to influence insulin resistance. Bidirectional mediation analyses indicated that bacterial function or faecal histidine might causally mediate an impact of Pichia on blood cholesterol.

CONCLUSION

We depict the sociodemographic and dietary determinants of human gut mycobiome in middle-aged and elderly individuals, and further reveal that the gut mycobiome may be closely associated with the host metabolic health through regulating gut bacterial functions and metabolites.

Nondestructive classification of soft rot disease in napa cabbage using hyperspectral imaging analysis

Identification of soft rot disease in napa cabbage, an essential ingredient of kimchi, is challenging at the industrial scale. Therefore, nondestructive imaging techniques are necessary. Here, we investigated the potential of hyperspectral imaging (HSI) processing in the near-infrared region (900–1700 nm) for classifying napa cabbage quality using nondestructive measurements. We determined the microbiological and physicochemical qualitative properties of napa cabbage for intercomparison of HSI information, extracted HSI characteristics from hyperspectral images to predict and classify freshness, and established a novel approach for classifying healthy and rotten napa cabbage. The second derivative Savitzky–Golay method for data preprocessing was implemented, followed by wavelength selection using variable importance in projection scores. For multivariate data of the classification models, partial least square discriminant analysis (PLS-DA), support vector machine (SVM), and random forests were used for predicting cabbage conditions. The SVM model accurately distinguished the cabbage exhibiting soft rot disease symptoms from the healthy cabbage. This study presents the potential of HSI systems for separating soft rot disease-infected napa cabbages from healthy napa cabbages using the SVM model, especially under the most effective wavelengths (970, 980, 1180, 1070, 1120, and 978 nm), prior to processing. These results are applicable to industrial multispectral images.

Potential for Biological Control of Pythium schmitthenneri Root Rot Disease of Olive Trees (Olea europaea L.) by Antagonistic Bacteria

Several diseases affect the productivity of olive trees, including root rot disease caused by Pythium genera. Chemical fungicides, which are often used to manage this disease, have harmful side effects on humans as well as environmental components. Biological management is a promising control approach that has shown its great potential as an efficient eco-friendly alternative to treating root rot diseases. In the present study, the antagonistic activity of ten bacterial isolates was tested both in vitro and in planta against Pythium schmitthenneri, the causal agent of olive root rot disease. These bacterial isolates belonging to the genera Alcaligenes, Pantoea, Bacillus, Sphingobacterium, and Stenotrophomonas were chosen for their potential antimicrobial effects against many pathogens. Results of the in vitro confrontation bioassay revealed a high reduction of mycelial growth exceeding 80%. The antifungal effect of the volatile organic compounds (VOCs) was observed for all the isolates, with mycelial inhibition rates ranging from 28.37 to 70.32%. Likewise, the bacterial cell-free filtrates showed important inhibition of the mycelial growth of the pathogen. Overall, their efficacy was substantially affected by the nature of the bacterial strains and their modes of action. A greenhouse test was then carried out to validate the in vitro results. Interestingly, two bacterial isolates, Alcaligenes faecalis ACBC1 and Bacillus amyloliquefaciens SF14, were the most successful in managing the disease. Our findings suggested that these two antagonistic bacterial isolates have promising potential as biocontrol agents of olive root rot disease.