Effect of arsenic on the plant growth-promoting bacteria Azospirillum brasilense Az39

ARMENDARIZ AL; TALANO MA; MEDINA MI; AGOSTINI E

Workshop; II Workshop Latinoamericano sobre PGPR (2014); 2014

Effect of arsenic on the plant growth-promoting bacteria Azospirillum brasilense Az39. Armendariz Ana Laura, Talano Melina A., Medina María I, and Agostini ElizabethDepartamento de Biología Molecular, FCEFQyN, Universidad Nacional de Río Cuarto, Ruta Nacional 36 Km 601, CP 5800 Río Cuarto, Córdoba, ArgentinaContact: aarmendariz@exa.unrc.edu.ar IntroductionArsenic (As) is frequently found at high concentrations in Argentinean agriculture soils and groundwater. Particularly in soils, rhizospheric microorganisms play a crucial role since their metabolic abilities can affect As bioavailability, and consequently As phytotoxicity. The selection of symbiotic or free-living plant growth promoting rhizobacteria (PGPR) strains with remediation capabilities has been emphasized, because they can contribute with plant tolerance to As and/or limit the metalloid incorporation in their tissues. The aim of the present work was to study the effect of As on Azospirillum brasilense Az39, a PGPR strain with ability to increase the productivity of grain crops such as soybean, particularly: a) its growth under different As concentrations, b) exopolysaccharides (EPS) production, c) biofilm formation, d) motility and arsenic metabolism, since they could be considered as tolerance strategies.Materials and methodsTo analyze the effect of As on A. brasilense Az39 growth, the bacterium was grown in LB liquid medium supplemented with 25 µM, 500 µM and 5 mM of arsenate (AsV) and arsenite (AsIII). For that, DO620 nm values were registered during 26 h and also FCU/ml were determined. For other analyses 25 and 500 µM of both As salts were used, with the exception of As metabolic analysis where only 25 µM was used. The effect of As on EPS production was determined through Anthrone method from bacterial cultures grown during 24 h in LB medium. Biofilm analysis was carried out by a spectrophotometric method using violet crystal (Abs570nm) and the assay was carried out in tubes. Motility was analyzed in LB diluted solid medium supplemented with 25 and 500 µM of AsV or AsIII. Swarming and swimming rings were expressed as ring diameter (cm). Total residual As, species (AsV and AsIII) concentration in the culture medium as well as As accumulation in bacterial pellet were measured by a graphite furnace atomic absorption spectrophotometric (GF-AAS).ResultsA. brasilense Az39 was able to grow in all tested conditions even at high AsIII concentration (500 µM), with the exception of 5 mM AsIII where growth was completely inhibited. EPS and biofilm production showed statistically significant increase under 500 µM AsIII, coinciding with the condition at which growth and motility (swarming and swimming) were seriously affected. When A. brasilense Az39 was grown in the presence of AsV, it was able to reduce around 36% of initial AsV. Moreover, it showed higher efficiency for AsIII oxidation (around 53%) and was able to accumulate an 8.5% of the total As in cell biomass under this condition.ConclusionA. brasilense Az39 motility and biofilm/EPS production remained unchanged, which correlates with the observed higher tolerance of this strain to AsIII. Therefore, the higher AsIII tolerance, ability for AsIII oxidation and As accumulation of A. brasilense Az39 suggest that an inoculation strategy with this strain would improve the development of soybean plants under As stress. Areas temáticas propuestas: Aplicaciones ambientales y Bio-remediación [6] y Taxones PGPR [1].