ETD

• AMF endosimbionts
• AMF spore-associated bacteria
• plant growth promoting bacteria
• Racocetra fulgida
• Racocetra persica

Arbuscular mycorrhizal fungi (AMF) are key plant symbionts enhancing plant nutrition and stress resilience. Their spores host diverse bacterial communities whose ecological and biotechnological roles remain poorly explored. This thesis investigated bacteria strictly associated with AMF spores isolated from the rhizosphere of Ammophila arenaria growing in coastal sand dunes. Metabarcoding showed that the spores of the two most abundant AMF species, Racocetra persica and Racocetra fulgida, harboured bacterial communities mainly belonging to Actinomycetota, Alphaproteobacteria and Gammaproteobacteria and to the endosymbionts Ca. Moeniiplasma glomeromycotorum and Ca. Glomeribacter gigasporarum. Community composition differed between species, with R. persica hosting the most complex microbiota. Culture dependent approaches allowed the screening of 246 bacterial isolates for plant growth promoting traits, including EPS production, salinity tolerance, ACC deaminase activity and IAA production. The molecular identification revealed Alkalihalobacillus rhizosphaerae, Bacillus mojavensis, Cytobacillus oceanisediminis, Duffyella gerundensis, Exiguobacterium spp., Niallia nealsonii, Peribacillus spp. and Priestia spp. as the 13 best performing bacterial isolates. Multivariate analysis highlighted Priestia sp. TSAT1 and Peribacillus sp. TSAT20 as the most promising multifunctional strains for potential use as biofertilizers.