Extracellular polysaccharides are involved in the attachment of Azospirillum brasilense and Rhizobium leguminosarum to arbuscular mycorrhizal structures

Arbuscular mycorrhizal (AM) fungi, one of the most important component of t he soil microbial community, establish physical interactions with naturally occurring and genetically modified bacterial biofertilizers and biopestici des, commonly referred to as plant growth-promoting rhizobacteria (PGPR). W e have used a genetic approach to investigate the bacterial components poss ibly involved in the attachment of two PGPR (Azospirillum and Rhizobium) to AM roots and AM fungal structures. Mutants affected in extracellular polys accharides (EPS) have been tested in in vitro adhesion assays and shown to be strongly impaired in the attachment to both types of surfaces as well as to quartz fibers. Anchoring of rhizobacteria to AM fungal structures may h ave special ecological and biotechnological significance because it may fac ilitate colonisation of new rhizospheres by the bacteria, and may be an ess ential trait for the development of mixed inocula.