Effective colonization of spinach root surface by Rhizobium

Abstract

Plant growth-promoting rhizobacteria are a group of bacteria able to promote plant growth and increase crop productivity. For a successful and effective bacteria-plant association, microorganism colonization and its arrangement and abundance on plant root surfaces are very important. Here, we analysed the ability of the strain PEPV12 identified as Rhizobium sp., to colonize spinach (Spinacia oleracea) root surfaces, and evaluated three parameters of in vitro plant growth promotion: (i) siderophore production, (ii) phosphate solubilization and (iii) indole acetic acid production. Moreover, we tested in vitro cellulose production and biofilm formation. Our results showed that this strain colonizes effectively and adheres to abiotic surfaces. Root colonization and adherence events were observed under fluorescence microscopy by using GFP-tagged PEPV12 strain, which was inoculated on spinach seedlings. Interestingly, we observed morphologic changes in root hairs, such as deformations and redirections at the tip in early stages of plant development of PEPV12 inoculated plants. Furthermore, we proceeded to evaluate in vitro plant development after inoculation of spinach seedlings with the strain of this study, showing significant differences in shoot length with respect to uninoculated plants. Our results showed that Rhizobium sp. PEPV12 actively and successfully colonizes spinach root surfaces, producing changes in root hairs and an increase in plant growth, suggesting its potentiality as a biofertilizer for Spinacia oleracea.