Fungal Volatile Organic Compounds: More Than Just a Funky Smell?

Many volatile organic compounds (VOCs) associated with industry cause adverse health effects, but less is known about the physiological effects of biologically produced volatiles. This review focuses on the VOCs emitted by fungi, which often have characteristic moldy or "mushroomy" odors. One of the most common fungal VOCs, 1-octen-3-ol, is a semiochemical for many arthropod species and also serves as a developmental hormone for several fungal groups. Other fungal VOCs are flavor components of foods and spirits or are assayed in indirect methods for detecting the presence of mold in stored agricultural produce and water-damaged buildings. Fungal VOCs function as antibiotics as well as defense and plant-growth-promoting agents and have been implicated in a controversial medical condition known as sick building syndrome. In this review, we draw attention to the ubiquity, diversity, and toxicological significance of fungal VOCs as well as some of their ecological roles.

Marvellous Muscodor spp.: Update on Their Biology and Applications.

Nearly 20 years ago, the first report appeared on the discovery of a novel genus-Muscodor. This organism was isolated as an endophyte from a cinnamon tree that had been introduced to Honduras from Sri Lanka in the early part of the last century. Characteristically, the original Muscodor albus, and all of its species isolated since that time are non-spore producers and each one exudes a characteristic spectrum of volatile bioactive compounds. The majority have a whitish mycelium, which is sometimes coiling, intertwined and decorated with variously shaped structures. Presently, there are at least 22 type species known/documented and each has been described as an endophyte from various plant families with widely varying habitats. An enormous variety of volatile organic compounds (VOCs) are produced by Muscodor spp. and some of these include esters, acids, aldehydes, ketones, aromatics, alkanes, alcohols, nitrosamides and terpenoids. The VOCs are both inhibitory and lethal to a wide variety of fungi and bacteria including some major pathogens of plants and humans. Interestingly, in almost all cases studied, no one compound by itself can mimic the bioactivity of the complete gas mixture, suggesting that the volatiles are acting in a synergistic manner and this has been tested with individual as well as the VOCs in various mixtures and concentrations. This review will discuss some of the recent findings in all aspects of this unique fungal genus whilst at the same time pointing out some of the major questions that remain about its biology, ecology and its applications in agriculture, medicine and other sectors. Most importantly, the authors provide arguments supporting the claim that Muscodor is taxonomically distinct from Induratia, a recently proposed change to its nomenclature.

Mycofumigation through production of the volatile DNA-methylating agent N-methyl-N-nitrosoisobutyramide by fungi in the genus Muscodor.

Antagonistic microorganisms produce antimicrobials to inhibit the growth of competitors. Although water-soluble antimicrobials are limited to proximal interactions via aqueous diffusion, volatile antimicrobials are able to act at a distance and diffuse through heterogeneous environments. Here, we identify the mechanism of action of Muscodor albus, an endophytic fungus known for its volatile antimicrobial activity toward a wide range of human and plant pathogens and its potential use in mycofumigation. Proposed uses of the Muscodor species include protecting crops, produce, and building materials from undesired fungal or bacterial growth. By analyzing a collection of Muscodor isolates with varying toxicity, we demonstrate that the volatile mycotoxin, N-methyl-N-nitrosoisobutyramide, is the dominant factor in Muscodor toxicity and acts primarily through DNA methylation. Additionally, Muscodor isolates exhibit higher resistance to DNA methylation compared with other fungi. This work contributes to the evaluation of Muscodor isolates as potential mycofumigants, provides insight into chemical strategies that organisms use to manipulate their environment, and provokes questions regarding the mechanisms of resistance used to tolerate constitutive, long-term exposure to DNA methylation.

Antifungal activity of volatile and non-volatile metabolites of endophytes of Chloranthus elatior Sw.

Agriculture crops that have fungal infections suffer significant economic losses and reduced crop output. Chemical fungicides are used to tackle the problem, although this has additional detrimental side effects. There is an urgent need for safe and novel antifungals. Volatiles from plant-beneficial endophytic fungi are considered promising alternatives for the biological control of fungal pathogens as a sustainable approach in an agroecosystem. In the present investigation, a volatile-emitting sterile endophytic fungus, Diaporthe sp. CEL3 with bio-fumigation activity, was isolated from leaves of the ethnomedicinal plant Chloranthus elatior Sw., collected from the Passighat forest of North-East India. The camphor odor volatiles of CEL3 showed an inhibitory effect against eight fungal pathogens in vitro and minimized the infections of Monilinia fructicola, a causal agent of cherry fruit rot, in VOC-exposed cherry fruits. Rhizoctonia solani, Botrytis cinerea, Pythium ultimum, and M. fructicola were maximally inhibited up to 51.5%, 55.8%, 61.9%, and 78.5%, respectively, in comparison to control by the volatiles. Another isolate, CEL7, identified as Curvularia sp., synthesized non-volatile, soluble antifungal metabolites in its cell-free extracts and exhibited antifungal action. Bioassay-guided fractionation revealed the presence of imidazole compounds- (2-aminoethyl)-1H-imidazole-2-carbaldehyde, Pyrazole 4, 5 imidazole, 1-formyl 3-ethyl, phenol compounds-Phenol, 4-[2-(methylamino) ethyl]-, 6-Nitro-3-chlorophenol, Phenol, 2,4,6-tri-tert-butyl-, etc., in the cell-free extracts, with a MIC value of 250-2,000 µg ml-1. Optimum VOC emission was achieved in a modified PDA medium with instantly smashed potato (150 g L-1), dextrose (20 g L-1), wheat husk (20 g L-1), and yeast extract (20 g L-1), with additional salts. Interestingly, endophytic CEL3 emitted different types of volatiles, and trans-verbenol (32.25%), geraniol (30.32%), trans-ocimenol (12.90%), and mentha-4,8-diene (5.16%) were the prime ones. These VOCs cause lethal leakage of protein and necessary intracellular molecules from the fungal pathogens. Thus, CEL3 could potentially be used as a bio-fumigating agent to control post-harvest infections caused by fungal pathogens. This study opens a new approach to the use of endophytic fungi in biocontrol.

Evaluation of Muscodor cinnamomi as an egg biofumigant for the reduction of microorganisms on eggshell surfaces and its effect on egg quality.

The presence of microorganisms on the eggshell surface is a factor of consideration in determining egg quality. These microorganisms can contribute to egg spoilage and can infect the egg. In this study, 18 morphotypes of microorganisms were isolated from eggshells. Morphological, biochemical, physiological and molecular analyses were used to identify these morphotypes into 7 species; Bacillus drentensis, Staphylococcus arlettae, Stap. cohnii, Stap. kloosii, Stap. saprophyticus, Stap. sciuri and Stap. xylosus. The potential of Muscodor cinnamomi to reduce the presence of microorganisms on eggshells by biological fumigation was investigated. The result showed that 16 strains of the tested microorganisms were inactivated after the exposure of the fungal volatile organic compounds. The most abundant compound was 2-methylpropanoic acid, followed by 3-methylbutan-1-ol. Our results indicated that a 24-h period of fumigation of 100g rye grain culture of M. cinnamomi was the minimum dose that could significantly reduce the number of microorganisms on the eggshell surface. Fumigated eggs from both box and cabinet fumigation trials showed significantly lower microbial numbers on the eggshell than non-fumigated eggs during the storage period of 14days. It was found that the values of the yolk index, albumen index and the Haugh unit of the eggs decreased during this storage time. However, those values of the fumigated eggs from both fumigation trials were found to be significantly higher than the non-fumigated eggs after the 24-h fumigation period and following storage for 5, 7 and 14days. However, the values of the albumen index were not found to have significantly increased over 5days of the box trial. This study is the first to report on mycofumigation activity for the purposes of reducing the presence of microorganisms on the surface of eggshells.

Muscodor kashayum sp. nov. - a new volatile anti-microbial producing endophytic fungus.

Muscodor kashayum (MycoBank no.: MB 803800; GenBank no.: KC481680) is a newly described endophytic fungus of a medicinal plant Aegle marmelos (Bael tree), growing in the tropical conserved rainforest in the Western Ghats of India. Muscodor kashayum possesses distinct morphological, molecular and physiological features from the earlier reported Muscodor species. The fungus forms characteristic rings of the ropy mycelium on potato dextrose agar medium. This sterile fungus is characterised by the presence of a pungent smell which is attributable to a blend of more than 23 volatile organic constituents, predominantly 3-cyclohexen-1-ol,1-(1,5-dimethyl-4-hexenyl)-4-methyl; 1,6-dioxacyclododecane-7,12-dione; 2,6-bis(1,1-dimethylethyl)-4-(1-oxopropyl) phenol; 2,4-di-tert-butylthiophenol and 4-octadecylmorpholine. In the in vitro anti-microbial assay using M. kashayum, growth of 75% of test fungi/yeasts and 72% of the test bacteria were completely inhibited. Therefore, M. Kashayum holds potential for future application to be used as a myco-fumigation agent.