Study of Products from Neutrophilic Iron Bacteria by Prompt Gamma/Neutron Activation Analysis and X-Ray Diffraction

Abstract

The Fe(II)-oxidizing bacteria (FeOB) and Fe(III)-reducing bacteria (FeRB) were among the first groups of microorganisms to be recognized for carrying out a fundamental geological process - the bacterial iron redox cycling. The deposition of iron ions by the bacteria from the Sphaerotilus-Leptothrix group of neutrophilic FeOB is extracellular in the form of biogenic products contained in tubular structures (sheaths). We report on the determination of the concentration of elements in these products and the relative amounts of biogenic iron oxides/(oxy) hydroxides resulting from the bacterial metabolism. The Fe(II)-oxidizing organism was isolated from freshwater wetland surface sediments in Vitosha Mountain. Biogenic nanostructured materials were obtained after growing the genus Leptothrix in SIGP and Adler’s nutrient media. Formation of sheaths was observed only in case of dynamic cultivation in SIGP medium. High enrichment level of iron was found by the PGAA and NAA techniques in the products of cultivated isolates as compared to the reference sample (product of nature). Three iron oxide phases were found after cultivation in Adler’s medium: lepidocrocite (γ-FeOOH), non-stoichiometric magnetite (Fe3-xO4) and goethite (α-FeOOH). The cultivation in the SIGP medium yielded a single phase bacterial product –lepidocricite of poor crystallinity.