Fingerprints of partial oxidation of biogenic magnetite from cultivated and natural marine magnetotactic bacteria using synchrotron radiation

Abstract

Magnetotactic bacteria are a multi-phyletic group of bacteria that synthesize membrane-bound magnetic minerals. Understanding the preservation of these minerals in various environments (e.g., with varying oxygen concentrations and iron supply) is important for understanding their role as carriers of primary magnetizations in sediments and sedimentary rocks. Here we present X-ray near edge structure (XANES) spectra for Fe in magnetotactic bacteria samples from recent sediments to assess surface oxidation and crystal structure changes in bacterial magnetite during early burial. Our results are compared with a XANES spectrum of cultivated Magnetofaba australis samples, and with magnetic properties, and indicate that oxidation of magnetite to maghemite increases with depth in the sediment due to longer exposure to molecular oxygen. These results are relevant to understanding magnetic signatures carried by magnetofossils in oxic sediments and sedimentary rocks of different ages.

Microbe‐Mediated Extracellular and Intracellular Mineralization: Environmental, Industrial, and Biotechnological Applications

“…Those present in magnetofossils also provide important information for reconstruction of the earth's archaic magnetic field. [ 61 ]…”

Diagenetic Fate of Biogenic Soft and Hard Magnetite in Chemically Stratified Sedimentary Environments of Mamanguá Ría, Brazil

“…Magnetite and hematite are also produced during pedogenesis, so that erosion and transportation of soil particles into the ría will contribute to sedimentary magnetism. High oxygen concentrations in the uppermost Mamanguá Ría sediment column cause oxidation of magnetite crystals, which is evident in synchrotron analyses that reveal progressive oxidation state changes of Fe (Rodelli et al, ). Magnetic analyses indicate little change from the magnetic signatures of pristine biogenic magnetite (Rodelli et al, ).…”

“…High oxygen concentrations in the uppermost Mamanguá Ría sediment column cause oxidation of magnetite crystals, which is evident in synchrotron analyses that reveal progressive oxidation state changes of Fe (Rodelli et al, ). Magnetic analyses indicate little change from the magnetic signatures of pristine biogenic magnetite (Rodelli et al, ). This is mainly due to the fact that magnetosome crystals in living magnetotactic bacteria are encapsulated by a protein membrane (Bazylinski et al, ).…”

“…This is mainly due to the fact that magnetosome crystals in living magnetotactic bacteria are encapsulated by a protein membrane (Bazylinski et al, ). Burial under oxidizing conditions will cause gradual oxidation of magnetite, but the magnetic properties and characteristic morphologies and sizes of magnetite magnetosomes remain detectable despite oxidation (e.g., Chang et al, ; Rodelli et al, ; Yamazaki & Shimono, ). In order to understand relationships between biogenic magnetite and the environments in which MTB lived, we assess variables that could have affected its formation and preservation.…”

Presence of biogenic magnetite in ferromanganese nodules

“…The FORC signatures were slightly wider at around 30 mT and narrower at 60 mT. FORC diagrams of magnetofossils from the literature, both cultivated and uncultivated predominantly have a narrow horizontal ridge with the primary peak in the region of 20–40 mT (Yamazaki, ; Abrajevitch and Kodama, ; Jovane et al ., ; Roberts et al ., , ; Rodelli et al ., ).…”