Program Book - 27th Fungal Genetics Conference

CONCURRENT SESSION ABSTRACTSThe mixed fungal and bacterial origin of truffle aroma. Richard Splivallo 1 , Aurélie Deveau 2 , Nayuf Valdez 1 , Nina Kirchhoff 1 , Pascale Frey-Klett 2 , PetrKarlovsky 1 . 1) Molecular Phytopathology and Mycotoxin Research, Georg-August University of Goettingen, Grisebachstrasse 6, Germany; 2) UMR1136INRA Université de Lorraine "Interactions Arbres/Micro-organismes", Labex ARBRE, IFR110 EFABA, Centre INRA of Nancy, 54280 Champenoux, France.Truffles are symbiotic ectomycorrhizal fungi which develop on plant roots. Their fruiting bodies are highly appreciated by humans for their aroma, whichtypically comprises twenty to fifty volatiles per truffle species. The biosynthetic routes leading to characteristic truffle volatiles have not yet been fullycharacterized. By similarity to yeasts, volatile synthesis in truffles most likely involves amino acid and fatty acid catabolism. Truffle fruiting bodies furthercontain a diverse microbial community which might be able to generate volatiles or biotransform volatile-precursors on its own. Our aim was toinvestigate the formation of sulphur containing volatiles in truffles, because sulphur volatiles play a major role in the truffle ecology and are determinantof their quality (for humans). We demonstrate that sulphur volatiles characteristic of the white truffle T. borchii are actually produced by bacteriacolonizing truffle fruiting bodies. Under laboratory bioassays, sulphur containing compounds (thiophenes volatiles) resulted from the transformation bybacteria of non-volatile precursor(s) into volatiles. Interestingly in our assays thiophene volatiles were detectable only from bacteria and not from trufflemycelium, while other compounds such as dimethyl disulfide were detectable from both organisms. This indicates that some volatiles might be producedby both truffle mycelium and bacteria, but thiophene volatiles most likely originate from bacteria only. Characterization of the bacterial population byFluorescence In Situ Hybridization highlighted that the concentration of thiophene volatiles correlated with the bacterial density inside fruiting bodies. Thisgives further ground to the bacterial origin of thiophene volatiles. Additionally the production of thiophene volatiles was suppressed upon treating trufflefruiting bodies with antibacterial or antifungal agents, suggesting that the precursors of thiophene volatiles might be synthesized by both fungi andbacteria. These unexpected results disprove the earlier belief that truffles were able to synthesize their aroma on their own. They add a new dimension toplant-fungal interactions by highlighting the importance of the bacterial community associated to truffle fruiting bodies.60