Phenotypical analysis searching for PGPR activities in Burkholderia species isolated from Argentinean soils

BIALER, M.; ANTONICH, N. ; DEGROSSI, J.; WALL, L.G.; DRAGHI W. O.; ZORREGUIETA, A.

Rosario

Congreso; IX Congreso Argentino de Microbiología General; 2013

Sociedad Argentina de Microbiología General

Burkholderia are ubiquitous bacterial species able to occupy a wide range of niches in nature, as soils, water sources, plantsand mammalians, and fulfilling diverse functions in their habitats, from beneficial agents to pathogenic behavior against plants or humans. The phylogenetic analysis of the genera allows classifying the species into two main clusters: the Burkholderia cepacia complex (BCC), which includes human and plant pathogen species, and Plant associated beneficial and environmental group (PBE), which is composed by species showing PGPR or xenobiotic-degradation traits.In the context of the BIOSPAS research consortium (Biología del Suelo para una Agricultura Sustentable), we performed asurvey in central Argentinean soils to characterize the actual biodiversity of Burkholderia species present in agricultural soils, and the effect that different crop practices have on the diversity status of this bacterial genus. We found that the diversity of species from Burkholderia genus decreases in soils with non-sustainable agricultural practices, while an augmented proportion of BCC species was observed.During the surveys we isolated 90 strains belonging to PBE group. These strains isolates belong to B. phymatum, B. terricola, B.graminis, B. tuberum, B. caribensis and B. caledonica species. With this set of strains we performed different experimental approaches to determine the presence of plant growth promoting traits. In vitro assays allowed us to determine severalsignificant properties to plant growth promotion: protease activity, phosphate solubilization and production of fluorescent compounds. The results showed that 10% of the strains exhibit proteolytic activity in skim milk agar. Besides, 45% formed a clear halo around the colony in Pikovskaya Agar, which is used for detection of phosphate-solubilizing soil microorganisms. The production of fluorescent compounds on King B medium, which indicates the synthesis of fluorescein, was not detected. We also carried out in planta experiment with the aim to observe the growth promotion activity of strains on wheat seedling. The results showed that 9% of isolates promote root growth in wheat seedlings through an increased development of root surface  area.We are particularly interested in strains that demonstrate more than one activity, as for example inorganic phosphorussolubilization and promotion of root development in wheat. Further studies on larger scales must be performed in order toconfirm the PGPR activity of the strain candidates and evaluate them as potential biofertilizers for crops.