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Project Progress

Although the average crustal abundances and concentrations in surface waters of Fe, Mn, Zn, Ni, Cu, Co, and Mo are extremely low, each of these metals is used in bacterial enzymes, coenzymes, and cofactors. While it is well known that bacteria excrete siderophores to extract Fe from their environment, it is not understood how these siderophores attack minerals to provide the FeIII, nor is it understood how bacteria extract other micronutrients. We are investigating how soil microbes extract these metals from common minerals. Our work has progressed most rapidly with investigations of hornblende. Leaching of metals from hornblende by microbes is being investigated in order to 1) determine the mechanisms of metal mobilization by soil microbes 2) determine whether natural mineral surface chemistry documents biotic metal extraction 3) determine whether iron isotope ratios of leached Fe is diagnostic of bacterial activity.

Isolates from an Adirondack soil containing hornblende were cultured in enriched medium. Partial sequencing of the 16s rRNA gene (Nucleic Acid Facility, Life Sciences Consortium, Penn State) of two aerobes capable of mobilizing Fe from hornblende showed that the two isolates are probably a streptomycete and an arthrobacter. In buffered media, the streptomycete and arthrobacter significantly increased the Fe release rate from hornblende over abiotic controls. Two different catechol siderophores produced by the isolates and characterized by high performance liquid chromatography (HPLC) and mass spectrometry (MS) are presumed to cause this Fe release enhancement. X-ray photoelectron spectroscopy (XPS) of hornblende planchets after dissolution in the presence of the arthrobacter revealed a substantial drop in the Fe/Si ratio of the hornblende surface after removal of the bacteria as compared to control samples treated in media w/o bacteria.