Volatile organic compounds of diverse origins and their changes associated with cultivar decay in a fungus-farming termite

Fungus-farming termites cultivate a Termitomyces fungus monoculture in enclosed gardens (combs) free of other fungi, except during colony declines, where Pseudoxylaria spp. stowaway fungi appear and take over combs. Here, we determined Volatile Organic Compounds (VOCs) of healthy Macrotermes bellicosus nests in nature and VOC changes associated with comb decay during Pseudoxylaria takeover. We identified 443 VOCs with unique volatilomes across samples and nest volatilomes mainly being composed of fungus comb VOCs with termite contributions. Few comb VOCs were linked to chemical changes during decay, but longipinocarvone and longiverbenone were only emitted during comb decay. These terpenes may be involved in Termitomyces defence against antagonistic fungi or in fungus-termite signalling of comb state. Both comb and Pseudoxylaria biomass volatilomes contained many VOCs with antimicrobial activity that may serve in maintaining healthy Termitomyces monocultures or aid in the antagonistic takeover by Pseudoxylaria during colony decline. We further observed a series of oxylipins that are known to serve diverse functions in the regulation of fungus germination, growth, and secondary metabolite production. Our volatilome map of the fungus-farming termite symbiosis provides new insights into the chemistry regulating complex interactions and serves as a valuable guide for future work on the roles of VOCs in symbioses.

Methods
This dataset contains the raw unprocessed .netCDF files from GC-MS analyses (with thermal desorption) of VOCs collected from Macrotermes bellicosus fungus-farming termite nests. Samples consists of headspace VOCs collected from three natural nests in-situ as well as healthy fungus combs, decaying combs and biomass from the stowaway competitor fungus, Pseudoxylaria originating from each of the three nests. All samples originate from M. bellicosus colonies in the area surrounding the Lamto Ecological Research Station (6°13′01.6″ N, 5°01′31.6″ W) in Côte d’Ivoire.

The VOC were collected with two different dynamic sampling systems on hydrophobic sorbent tubes (150 mg Tenax TA/200 mg Carbograph 1TD (#C2-AXXX-5032), Markes International, Llantrisant, UK). Nest headspace VOCs were collected with a Pocket pump (50 ml/min; TOUCH; SKC Ltd., Blandford Forum, UK) while Pseudoxylaria, fungus comb and decaying comb headspace VOCs were collected for 15 min with a push-pull headspace sampling system with the samples placed inside a pre-cleaned (60 min, 120 °C) Polyethylene terephthalate (PET) oven bag. Air inlets and outlet tubes were inserted through holes cut in opposite corners of the bag and secured tightly closed using metal wire to prevent contamination from ambient air. Air flows were controlled by battery-operated pumps (12 V; Rietschle Thomas, Puchheim, Germany) with flow rates of 200 ml/min for incoming air and 150 mL min-1 for outgoing sample air.