Isolation and Characterization of Microorganisms that may Play a Role in White Truffle Mycorrhization and Fruitbody Production

Truffles are ascocarps produced from ectomycorrhizal ascomycetes belonging to Tuber spp.. Among all truffles, Tuber magnatum Pico is the most appreciated because of its peculiar taste and aroma. However, basic aspects of the biology of this Tuber species have not been fully elucidated. To date, cultivation of T. magnatum (white truffle) is still challenging and the reason is still unclear. In fact both the life cycle and soil/environmental conditions stimulating mycorrhizae and ascocarps formation in Tuber magnatum still remain unknown. Several studies have suggested a role played by bacteria, fungi and yeasts in the development of truffle fruit bodies and aromas but data are lacking for white truffle. The aim of this study was to describe the whole microbial composition present in two different natural orchards. The analysis was carried out on nine ascocarps and on soil samples collected at four distances (from 0.20 to 2 meters) from the place where each ascocarp was retrieved. Microorganisms were isolated both from the inside and the outside of each ascocarp as well as from each soil sample. DNA was isolated from all colonies and used for molecular characterization: ITS (Internal Transcribed Spacer rDNA) for Fungi (including yeasts), and 16S for Bacteria. Our analyses revealed a high level of microbial diversity in these samples, which increased proportionally to the distance from the fruitbody. In contrast, low but distinct fungal and bacterial diversity level was found inside ascocarp indicating that truffle fruitbodies select for a distinct microbiome. For instance Hypocreales dominated, but Sarcoscyphaceae and Pyronemataceae were also isolated from the peridium, while Herpotrichiellaceae and Cladosporiaceae were isolated mostly from the gleba. These results will be discussed in more detail pertaining to the autecology and microbiology of Tuber magnatum.