Start Date: Feb 28, 2012
End Date: Mar 14, 2015
Experiments will be conducted in plastic microcosms containing sterile soil amended with grains of sand coated with radioactively labeled iron or manganese. The sand will be prepared by established procedures and characterized for surface area, porosity, microscopic morphology (SEM), structure (x-ray diffraction) and iron (Fe) and manganese (Mn) concentration. Plastic columns filled with soil and containing each labeled sand will be sown with wheat seeds inoculated with Pseudomonas fluorescens strain 2-79 or a mutant deficient in the production of phenazine-1-carboxylic acid (PCA). Soils will be maintained at different water potentials. Controls will be sterilized soil plus sand (coated or noncoated) with and without plants. After several weeks of growth, shoots and roots will be harvested, washed free of adhering soil or sand and extracted to remove and quantify extracellular Fe and Mn. Roots and shoots will be prepared for liquid scintillation counting of labeled and total Fe and Mn. The ratio of the radioisotope to the total will allow calculation of the fraction of metal supplied by the coated sand. The growth medium will be extracted with water for determination of total soluble Fe and Mn. Sand grains will be separated from the soil by dry sieving and analyzed to determine final Fe and Mn concentrations and any physical, structural or morphological changes of the oxide coatings. Individual grains differing in distance from the root and root apex also will be selected in order to determine if dissolution of the oxide is dependent on location. Populations of PCA-producing strain 2-79 or the non-producing mutant strains will be determined and PCA produced in situ will be extracted and quantified.