The microbiome structure of the symbiosis between the desert truffle Terfezia boudieri and its host plant Helianthemum sessiliflorum

The desert truffle Terfezia boudieri forms mycorrhizal relations with the roots of its host plant Helianthemum sessiliflorum. In the symbiosis, the fungus enhances plant productivity by increasing minerals uptake, water supply and resistance to biotic and abiotic stresses. These activities requires the cooperation with soil bacteria forming tripartite relations. However, the diversity, composition, and roles of the bacterial community under field conditions in the Negev desert is unknown. Our overall goal is to study the contribution of soil microbial communities to the establishment of the mycorrhizal symbiosis.

Bacterial DNA was isolated from fruit bodies (internal and external), mycorrhizal roots and mycorrhizosphere soil. Meta-analyses of the 16S-rRNA revealed that bacterial communities of fruit bodies differ from those of roots and soil. Families of Actinobacteria, Planctomycetes, Proteobacteria, and Saprospiraceae are present in all four samples. Our hypothesis that host plants confer extensively to the microbial richness and diversity in the field was experimentally confirmed. The α-diversity analysis revealed that soil and roots contain significantly more bacterial species than fruit samples. Shanon index and Chao1 revealed that bacterial abundance in fruits internal samples was comparatively lower. Probably fruit internal factors restrict bacterial communities to form a specific population. Soil analyses indicate an increase in soluble potassium and nitrogen due to bacterial activity which is affected by bacterial composition and selection of population by the host plant.

Describing the bacterial structural diversity and functions is the basis for further studies to identify active bacterial strains that contribute to the symbiosis.