Fungal and Bacterial Diversity in the Tuber magnatum Ecosystem and Microbiome

Fungi belonging to the genus Tuber produce edible ascocarps known as truffles. Tuber magnatum Picco may be the most appreciated truffle species given its peculiar aroma. While its life cycle is not yet fully elucidated, some studies demonstrated an active role of microorganisms. The main goal of this study was to determine how the T. magnatum microbiome varies across space and time. To address this, we characterized microbial communities associated with T. magnatum through high-throughput amplicon sequencing of internal transcribed spacer (ITS) and 16S rDNAs in three productive natural sites in Italy across 2 years. At each site, four truffles were sampled as well as the soil underneath and at 40, 100, and 200 cm from the harvesting points, to assess for microbial variation between substrates, years, and sites. A statistically significant site-related effect on microbial communities was identified, whereas only the prokaryotic community was significantly affected by the distance of soil from the truffle. Significant differences between sampling years were also found, demonstrating a possible relation among rainfall precipitation and Firmicutes and Actinobacteria. Thirty-six bacterial OTUs in truffles and 11 bacterial OTUs in soils beneath truffles were identified as indicator taxa. As shown for other truffle species, the dominance of Bradyrhizobium, Rhizobium, and Ensifer spp. within the truffle fruiting body suggests an evolutionary adaptation of this microorganism to the genus Tuber. The present work offers novel and relevant insights into the microbial ecology of T. magnatum ecosystems and fruiting bodies. The function and role of these bacteria in the truffle microbiome and life cycle are in need of further investigation.