Bacteria associated with a commercial AMF inoculum: community composition and multifunctional activity as assessed by Illumina sequencing and culture-dependent tools. Bacteria associated with a commercial AMF inoculum

The most important players of soil biological fertility are represented by arbuscular mycorrhizal fungi (AMF), beneficial soil microorganisms, able to modulate biochemical and physiological soil processes, and to affect its biological and nutritional characteristics. AMF, establishing symbioses with the roots of most land plants, facilitate plant nutrient uptake, protect plants from biotic and abiotic stresses and provide essential ecosystem services. However, such beneficial services are the outcome of the synergistic action of AMF and the vast communities of mycorrhizospheric bacteria living strictly associated with their mycelium and spores. Two main strategies have been devised to exploit the benefits deriving from the mycorrhizal symbionts: the adoption of specific management practices and the use of AMF inoculation. Many types of commercial AMF inoculum are available on the market, obtained from greenhouse multiplication on mycotrophic trap plants where a rich community of bacteria thrive and exert important functional activities. Here, for the first time, we explored the bacterial metagenome of a commercially available AMF inoculum by Illumina high-throughput sequencing, a method able to provide information about culturable and unculturable members of the inoculum microbiota. Moreover, we isolated and characterized culturable bacteria showing important PGP traits, as the ability to produce IAA and siderophores, to be utilized, individually and/or in multispecies consortia with AMF as beneficial biofertilizers/bioenhancers in sustainable agroecosystems