Genomic and phylogenomic analyses of Bradyrhizobia associated with Tuber magnatum

Jacopo Vujovic ¹, Simone Graziosi ¹, Benucci Gian ², Federico Puliga ¹, Mirco Iotti ³, Antonella Amicucci ⁴, Gregory Bonito ², Alessandra Zambonelli ¹

Università di Bologna ¹, Michigan state University ², Università degli studi dell'Aquila ³, Università di Urbino ⁴

The white truffle (Tuber magnatum Picco) is the most prized truffle, but cultivating it on a large scale remains challenging compared to other valuable Tuber species. Moreover, the mycelium of T. magnatum has not been successfully cultivated until recently, posing significant challenges in experimental settings. In our recent work Graziosi et al. 2024, we identified beneficial interactions between T. magnatum mycelium and Bradyrhizobia. These interactions enable the successful in vitro growth of T. magnatum mycelium. Both the isolated T. magnatum and the associated bacteria showed a mutual dependency on modified Woody Plant Medium (mWPM). Neither the bacteria nor the T. magnatum mycelium could grow independently on mWPM. Phylogenetic analyses using 16S rRNA, glnII, recA and nifH genes revealed that these bacterial strains are a monophyletic group, distributed across five subgroups. These strains belong to a previously undescribed lineage within the Bradyrhizobium jicamae supergroup of the Bradyrhizobium genus. In this study, we sequenced the genomes of two bacterial strains (17.3.1;41.3.2), which were associated with the most vigorous T. magnatum isolate (TMG5072). Using Element AVITI system we generated 150 bp paired-end reads. Phylogenomic analyses, conducted with over 400 single-copy orthologous genes conserved in bacteria (BUSCO), confirmed the placement within the B.jicamae supergroup. These strains are positioned in a new sister clade alongside the recently described species B. roseum. The ongoing analysis of the first two sequenced genomes aims to explore the metabolic potential of these bacteria, focusing on understanding their potential role in promoting the in vitro growth of T. magnatum, particularly in relation to carbohydrate and nitrogen metabolism. Establishing stable T. magnatum mycelial cultures and gaining a deeper understanding of the associated bacteria could lead to the development of new biotechnologies for cultivating the white truffle. Furthermore, this knowledge may provide a foundation for further studies on the biology of this species. Graziosi, S., Puliga, F., Iotti, M., Amicucci, A. & Zambonelli, A. (2024) In vitro interactions between Bradyrhizobium spp. and Tuber magnatum mycelium. Environmental Microbiology Reports, 16(3), e13271. https://doi.org/10.1111/1758-2229.13271

Main author career stage: Postdoc / Fellow

Contribution type: Talk

First choice session: 5. Genetics, genomics, and bioinformatics

Second choice session: 2. Ecology