Molecular and functional characterization of beneficial bacteria associated with AMF spores

In the years to come, a major challenge for agriculture will be the implementation of sustainable intensification of agricultural practice, to ensure sufficient food production for the growing global population and to reduce chemical and energy inputs. This aim may be pursued by promoting the efficient use of beneficial soil microorganisms that play fundamental roles in plant growth and health. Among them, arbuscular mycorrhizal fungi (AMF), and their associated microbiota, can be considered biofertilizers, bioenhancers, and biocontrol agents, showing diverse plant growth-promoting (PGP) properties. Here we focus on approaches for the study of the identity and function of bacteria associated with AMF spores, referred to as spore-associated bacteria (SAB). Culture-independent methods are essential for the identification of their diversity; however, only culture-dependent approaches allow the determination of SAB functional roles, and the selection of the best performing strains, to be tested in laboratory experiments, as well as in the field. The discovery of SAB functional activities, e.g., phosphate solubilization and nitrogen fixation, as well as production of phytohormones, siderophores, and antibiotics, is opening new avenues for their targeted management in agriculture. In this chapter the approaches, techniques, and results relevant to culture independent and culture-dependent studies on beneficial SAB will be reviewed. Significant case studies dealing with SAB utilization as inoculants in experimental trials will be discussed, with the aim of prospecting their utilization, individually or in specially designed multifunctional consortia, in sustainable and innovative food production systems.