Microbial Membrane Protein Extracts Electrons from Iron Nanoparticles
Iron plays a vital role in environmental biogeochemistry, exchanging electrons with microorganisms to transform more soluble Fe(II) to less soluble Fe(III). The iron cycle is also coupled to the climatically relevant carbon and nitrogen cycles, as well as other elemental cycles. By pulling apart the kinetics and detailed interactions between iron particles and microorganisms, researchers hope to gain insights into which aspects of these processes are important at larger scales. A team of scientists from Pacific Northwest and Lawrence Berkeley National Laboratories used stopped-flow spectrometry and micro X-ray diffraction at the Environmental Molecular Sciences Laboratory (EMSL) and X-ray absorption and magnetic circular dichroism spectroscopies at the Advanced Light Source (ALS) to investigate the oxidation kinetics of iron nanoparticles exposed to a bacterial protein, decaheme c-type cytochrome (Mto). When MtoA from Sideroxydans lithotrophicus was exposed to iron nanoparticles, the MtoA extracted electrons from the structural Fe(II) in the nanoparticles starting at the surface and then continuing to the interior, leaving behind the Fe(III) and not damaging the crystal structure. The team intends to further investigate this process using proteins known to transfer electrons in other environmentally relevant microorganisms, and using other types of iron-containing minerals. This research provides the first quantitative insights into the transfer of electrons from minerals to microbes, and provides a clear picture of how microorganisms accelerate or control iron biogeochemistry and cycling in natural systems. This knowledge sheds light on elemental cycling processes coupled to the iron cycle, including carbon, nitrogen, sulfur, and other metals.
Liu, J., C. I. Pearce, C. Liu, Z. Wang, L. Shi, E. Arenholz, and K. M. Rosso. 2013. “Fe3-xTixO4 Nanoparticles as Tunable Probes of Microbial Metal Oxidation,” Journal of the American Chemical Society 135(24), 8896–907. DOI: 10.1021/ja4015343.