Of the two nanocrystal (magnetosome) compositions biosynthesized by magnetotactic bacteria (MTB), the magnetic properties of magnetite magnetosomes have been extensively studied using widely available cultures, while those of greigite magnetosomes remain poorly known. Here we have collected uncultivated magnetite-and greigite-producing MTB to determine their magnetic coercivity distribution and ferromagnetic resonance (FMR) spectra and to assess the MTB-associated iron flux. We find that compared with magnetite-producing MTB cultures, FMR spectra of uncultivated MTB are characterized by a wider empirical parameter range, thus complicating the use of FMR for fossilized magnetosome (magnetofossil) detection. Furthermore, in stark contrast to putative Neogene greigite magnetofossil records, the coercivity distributions for greigite-producing MTB are fundamentally left-skewed with a lower median. Lastly, a comparison between the MTB-associated iron flux in the investigated estuary and the pyritic-Fe flux in the Black Sea suggests MTB play an important, but heretofore overlooked role in euxinic marine system iron cycle.
Bibliographical noteFunding Information:
This work was supported by the Higher Degree Research fund from Department of Environment and Geography, Macquarie University, and a visiting fellowship to the Institute for Rock Magnetism (IRM) to A.P.C. We thank the WHOI mooring team for the anchor and buoys loan, C. Lamborg (WHOI) for the sediment trap and YSI sensor loan, S. Simmons (MBL) for GeoPump loan and useful discussion, M. Johnson (WHOI) for site suggestion and access to the compound microscope, L. Kerr (MBL) for TEM fixative and phosphate buffer, D. Birch (Macquarie University) for helpful discussion and access to TEM, C. Taylor and Z. Mlodzinska (WHOI) for providing bench space for filtration and cell fixation, J. Sepulveda and F. Schubotz (MIT) for HgCl2 and access to freeze dryer, Princeton Measurement Corp for access to AGFM, A. Newell (North Carolina State University) for data and code for plotting putative sedimentary magne-tofossils dimensions, R. Egli (Central Institute for Meteorology and Geodynamics) for making available CODICA and GECA, R. Harrison (University of Cambridge) for making available FORCinel v.2.01, J. Parker for the bathymetry map for Upper Pond, and D. Barry and S. Barry for discussion. The IRM is supported by the Instruments and Facilities Program of the NSF Division of Earth Science. This is IRM contribution 1404.