Spore associated bacterial communities display patterns related to the arbuscular mycorrhizal host genotype in Mediterranean sand dunes

BACKGROUND: Arbuscular mycorrhizal fungi (AMF) are beneficial microorganisms establishing symbioses with the roots of most plants, supporting their nutrition and health, mainly in nutrient-poor and harsh environments. AMF spores host diverse bacterial communities whose distribution in the different taxa is poorly understood. To this aim we determined the entire diversity of spore associated bacteria thriving in Ammophila arenaria rhizosphere from Mediterranean maritime sand dunes by Illumina sequencing. RESULTS: The two most abundant AMF species, Racocetra fulgida and Racocetra persica disclosed a highly heterogeneous composition of spore bacterial communities. The endosymbiont Ca. Moeniiplasma glomeromycotorum was abundant in both AMF species and detected in R. fulgida for the first time. Ca. Glomeribacter gigasporarum was present only in R. persica. Distinct highly diversified spore-associated bacterial communities were also identified, with 251 Amplicon Sequence Variants (ASVs) affiliated to 69 and 34 genera in case of R. persica and R. fulgida, respectively. The regular detection of Actinomycetota confirmed a relatively stable relationship with AMF spores. Most of the identified bacteria belonged to culturable genera and species, reported to possess key beneficial activities. CONCLUSIONS: Our study showed that different AMF genotypes differentially recruited highly diversified and rich spore associated bacterial communities in a natural sand dune system. The isolation in pure culture of such bacteria could boost in-depth studies aimed at revealing their functional role in the complex interactions between AMF, associated bacteria and host plants and their possible exploitation in harsh agroecosystems.