Bioprospecting rhizosphere microbial communities associated with plants living in Mediterranean coastal sand dunes for enhancing plant drought tolerance

Climate change and global warming have contributed to increase terrestrial drought, causing serious negative impacts on agricultural production and posing severe threats to worldwide food security. Drought stress may be addressed by using beneficial soil microorganisms associated with plant roots, able to improve plant water-use and nutrient uptake efficiency, such as arbuscular mycorrhizal fungi (AMF), that establish mutualistic symbioses with the roots of most food crops and the bacteria strictly associated with their spores and mycelium. The aim of this study was to isolate and characterize AMF associated with the xerophytic plant Ammophila arenaria, adapted to the extreme environment of maritime sand dunes, and mycorrhizosphere bacteria, in order to select the best performing strains. The dominant AMF species retrived were Acaulospora scrobiculata, Glomus spp., Racocetra fulgida, Racocetra persica, Racocetra sp., Scutellospora sp. Bacterial strains, selectively isolated for resistance to desiccation, rhizosphere competence and functionally characterized for PGP traits, showed multifunctional properties, suggesting that, acting in synergy with AMF, they may provide additional benefits, improving the performance of drought-stressed plants. In particular, bacteria producing EPS may be crucial for plant performance during drought, as EPS are able to condition the rhizosphere microenvironment and to favour water retention, thus protecting roots against desiccation. Among the bacteria identified, members of Actinobacteria were regularly retrieved from all AMF isolates, confirming their widespread occurrence in the mycorrhizosphere as promoters of AMF activity and functionality. Interestingly, diverse bacterial communities were associated with the different AMF, although originated from the same host plants and environmental conditions, showing that each AMF isolate recruits on its spores a different microbiota. This work makes available AMF and bacterial isolates to be further tested in the formulation of effective microbial consortia, able to positively affect water and nutrient use efficiency, in turn enhancing crop productivity and resilience toward drought stress.