18 Fungal and Bacterial Volatile Organic Compounds: An Overview and Their Role as Ecological Signaling Agents

Abstract

Both fungi and bacteria emit many volatile organic compounds (VOCs) as mixtures of low molecular mass alcohols, aldehydes, esters, terpenoids, thiols, and other small molecules that easily volatilize. Most determination (separation and identification) of VOCs now relies on gas chromatography–mass spectrometry (GC-MS) but developments in “electronic nose” technology promise to revolutionize the field. Microbial VOC profiles are both complex and dynamic: the compounds produced and their abundance vary with the producing species, the age of the colony, water availability, the substrate, the temperature, and other environmental parameters. The single most commonly reported volatile from fungi is 1-octen-3-ol which is a breakdown product of linoleic acid. It functions as a hormone within many fungal species, serves as both an attractant and deterrent for certain species of arthropods, and exhibits toxicity at relatively low concentrations in model systems. Bacterial and fungal VOCs have been studied by scientists from a broad range of subdisciplines in both theoretical and applied contexts. VOCs are exploited for their food and flavor properties, their use as indirect indicators of microbial growth, their ability to stimulate plant growth, and their ability to attract insect pests. Because these compounds can diffuse a long way from their point of origin, they are excellent chemical signaling molecules (semiochemicals) in non-aqueous habitats and facilitate the ability of microbes to engage in “chemical conversations.” The physiological effects of bacterial and fungal VOCs in host–pathogen relationships and in mediating interspecific associations in natural ecosystem functioning is an emerging frontier for future research.