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Project Progress

Microbe-mineral interactions (dm)

Although the terrestrial 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 microbes 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. In previously reported work, we showed that microbes mobilize Fe from silicate minerals and that this Fe is isotopically light compared to the host mineral. In this past year, we have shown that microbes can mobilize Mo (Azotobacter vinelandii), Ni (Methanobacterium thermoautotrophicum), and Cu (Bacillus mycoides) from silicates. We are attempting to measure the isotopic signatures of these mobilized metals, using multi-collector inductively coupled plasma-mass spectrometry. We have also investigated mobilization of P from the common mineral apatite, and we have documented etch pit types formed as a consequence of biotic and abiotic etching. In this last project, we have also identified a technique to remove microbes from silicate surfaces without chemically or topographically disturbing the surface. Our progress has been very accelerated: we have found that every microbe tested has the ability to mobilize metals, when those metals are needed as micronutrients. Future work with isotopic measurements could identify a suite of biosignatures.