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Project Progress

Metals such as Fe, Mn, Ni, Cu and Mo are extremely low in abundance in natural waters, but are used in bacterial enzymes and cofactors. While it is well known that microbes secrete siderophores to extract Fe from their environment, it is not understood how these siderophores attack minerals to extract the FeIII, nor how bacteria extract other micronutrients. We have shown previously that microbes can mobilize Mo (Azotobacter vinelandii), Ni (Methanobacterium thermoautotrophicum), and Cu (Bacillus sp.) from silicates. We have also observed that macronutrients such as P can be extracted from earth materials, and that elements found in minerals such as S and Fe can be used as electron acceptors. Our work investigates the mechanisms and isotopic effects of these processes as well. Graduate student Libby Hausrath has also been investigating basalt and olivine weathering in a Mars analog environment, as described below.

Libby Hausrath attended the 2005 Arctic Mars Analog Svalbard Expedition (AMASE) in Svalbard. The Sverrefjell volcano in Svalbard is considered a Mars analog, because of carbonate globules found there which are very similar to carbonate globules found in meteorites from Mars. Weathered basalt samples were collected for analysis of biotic and abiotic weathering, and the potential identification of biomarkers. Samples of glass and olivine were buried for re-collection at a later date and analysis of weathering processes on these samples. The analysis of the biological extent of weathering (e.g. by lichens and fungi) in the field samples and buried samples, including the effect of potential complexing agents or ligands, will help in the identification of potential biomarkers on basalts, and in understanding the ways in which organisms interact with minerals to obtain trace metals needed for life. Data generated thus far by microscopic and spectroscopic methods indicate that physical weathering plays a larger role than chemical weathering in this environment.

Of the metal micronutrients, Fe, Mo, Ni, and W, we have found that the prokaryotes studied only release ligands to extract Fe and Mo: no ligands have been found to extract Ni and W by methanogens and hyperthermophiles respectively. We hypothesize that these latter two types of organisms may live upon a chemical reaction that yields energy at a low enough level that it is not energetically feasible to release high affinity ligands. We have published a paper on production of a “molybdophore” and extraction of Mo from a silicate by Azotobacter vinelandii (Liermann et al., 2005, Chem. Geol. 220: 285-302); we have also published a paper on reduction of goethite by Shewanella oneidensis membrane fractions (Ruebush et al., 2006, Geochim. Cosmochim. Acta 70: 56 – 70) and a paper on isotopic fractionation of Cu during oxidation of chalcocite by Acidothiobacillus ferrooxidans (Mathur et al., 2005, Geochim. Cosmochim. Acta 69: 5233 — 5246). We have submitted a paper investigating the role of cyanobacterial biopolymers on apatite dissolution and P utilization (Schaperdoth et al., 2006, submitted to Geomicrobiology Journal), and a paper investigating the potential for Ni biomarkers by methanogens (Hausrath et al., 2006, accepted by Astrobiology).

Work by Alexander Neaman has shown that mobility patterns of Al, Fe, P and Cu provide good indicators of the presence or absence of organic ligands in soils and paleosols (Neaman et al., 2005, Geology 33: 117 — 120; Neaman et al., 2005, American J. Science 305: 147 — 185; Neaman et al., 2006, American J. Science, in press).