AZOSPIRILLUM BRASILENSE AZ39 AND PANTOEA SP.: GFP- LABELLING AS A METHOD TO STUDY ROOT COLONIZATION

FAVALE N.; GROPPA M.D.; ROSELLO F.; ZAWOZNIK M.S.; DÍAZ HERRARA S.; BENAVIDES M.P.

Buenos Aires

Congreso; Reunión conjunta de sociedades de biociencias, LIII Reunión SAIB 2017; 2017

SAIB-SAIC-SAI-SAA-SAB-SAB-SAFE-SAFIS-SAH-SAP

Plant growth promoting rhizobacteria (PGPR) are associated with the roots of a wide variety of plant species leading to an increase of water and nutrients uptake, through diverse mechanisms.To obtain a tool for the study of root colonization by microorganisms, Azospirillum brasilense Az39 (a PGPR widely used in commercial formulations) and a strain of Pantoea sp. isolated from wheat were labelled with the green fluorescent protein (GFP). To demonstrate that bacterial labelling does not affect other bacterial properties, the dynamics of growth in liquid medium, biofilm formation (by violet crystal assay) and indole acetic acid (IAA) production (by Salkowski method) of wild type and GFP-labelled strains were studied. Preliminary results would indicate that GFP labelling did not affect IAA production of A. brasilense, whereas biofilm formation was lower in the transformed strain in LB medium. Great variability was observed in Nfb medium. The dynamics of in vitro multiplication, the growth in semisolid Nfb medium and the morphology of the colonies remained similar. Additionally, an inoculation assay of Arabidopsis thaliana plants was carried out. After 6 days of inoculation with A. brasilense, the plants showed an evident fluorescence in the roots denoting the presence of the bacteria. Fluorescence microscopy allowed to observe a great colonization of the surface root and a certain number of fluorescent cells arranged in a row inside a root segment, apparently colonizing a vascular bundle. While plants inoculated with labelled Azospirillum promoted root growth, inoculation with labelled Pantoea sp. negatively affected Arabidopsis plants and a significant chlorosis in the leaves was observed. Labelled strains are important tools to advance in the knowledge of the interaction between rhizospheric microorganisms and diverse crops of high economic impact for our country.