Adhesiveness and root hair deformation capacity of Azospirillum strains for wheat seedlings

Abstract

A binding assay for Azospirillum cells adsorbed to wheat roots was developed. It consisted of incubation exposing germinating seedlings to bacterial cells in liquid Fahreaus solution at 30°C for 2 h. The seedlings were removed and washed four times in Fahreaus solution followed by centrifugation for 15 min at 300 rev min −1 after every washing. The number of Azospirilla that remained attached to the roots was estimated by plating serial dilutions on agar media of root homogenates to enable colony counts. Optimal assay conditions for inoculum size, pH, age of the cultures and exposure time were determined. Binding kinetic data best fitted a Langmuir adsorption isotherm thus indicating a saturable, specific number of available sites on the roots for the adsorption of Azospirillum brasilense Sp245. Competition assays with different Rhizobium species were carried out showing a preferential adsorption for Azospirillum.