nai

Project Progress

Fe, Mn, Zn, Ni, Cu, Co, and Mo are extremely low in abundance in natural waters, but each of these metals is used in bacterial enzymes, coenzymes, 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 provide the FeIII, nor is it understood how bacteria extract other micronutrients. In previously reported work, we have shown that microbes can mobilize Mo (Azotobacter vinelandii), Ni (Methanobacterium thermoautotrophicum), and Cu (Bacillus sp.) from silicates. In addition, we have 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. Specifics are given below.

We showed that methanogens can grow without dissolved Ni as long as Ni is present in a solid substrate. Over the last year we tested whether this growth was due to 1) release of a ligand that extracted Ni, 2) release of lysates after cell death, 3) release of extracellular proteins that interact with the Ni substrate, or 4) pH changes associated with growth of the methanogen. Graduate student L. Hausrath has clearly shown that the Ni extraction that occurs is due to pH changes related to utilization of carbon dioxide. We have found little to no other evidence for how methanogens condition their environment for growth. We have similarly observed no evidence for release of ligands by hyperthermophiles living in medium without dissolved W.

Anabaena, a cyanobacterium, was grown with fluorapatite as sole phosphorous (P-) source for 7 days. An inorganic control, apatite + medium was also run without inoculation. At the end of the experiment, fluorapatite grains from the various treatments were compared using scanning electron micrograph (SEM). Enhanced etching of the apatite in the presence of the cyanobacterium as compared to the abiotic control accompanies the enhanced clumping of the Anabaena when grown in the absence of soluble P. We are still investigating what controls the clumping and the etching.

We continue to analyze respiration of Fe oxides using an in vitro model for Shewanella oneidensis. A paper was submitted to Environ. Sci. Technol. on this topic. In addition, we have been investigating the isotopic fractionation of Cu during bacterial oxidation of chalcocite, and we are writing a paper on this topic.