Magnetic Biosignatures of Magnetosomal Greigite From Micromagnetic Calculation

Abstract

Magnetotactic bacteria (MTB) produce intracellular ferrimagnetic crystals (magnetosomes) consisting of magnetite (Fe 3 O 4 ) or greigite (Fe 3 S 4 ) aligned in chains (e.g., Faivre & Schüler, 2008). These magnetosomes provide MTB a permanent magnetic dipole that orients the bacteria along geomagnetic field lines (magnetotaxis) to navigate toward optimal living conditions . Signatures from MTB can be used to trace Earth surface environmental conditions and biogeochemical cycles (e.g.,

Self‐Reversed Magnetization in Sediments Caused by Greigite Alteration

“…Some T‐type samples show complex mixture behavior and have medium coercivity values between the S‐ and M‐type samples (Figures S1 and S3, Tables S1 and S2 in Supporting Information ). Magnetic properties for the studied samples here are also different from those of typical biogenic greigite which have a central‐ridge FORC signature (Bai, Chang, Pei, et al., 2022; Chang et al., 2014; Chen et al., 2014; Reinholdsson et al., 2013).…”

Micromagnetic calculation of the magnetite magnetosomal morphology control of magnetism in magnetotactic bacteria

“…Microstructure models of realistic intact chains were created based on TEM images of MTB using Trelis 16.3 (figure 1). The information about particle position, size and rotation angle of intact magnetosome chains (table 1) was obtained from TEM images using the computer vision library OpenCV-Python (figure 1d) following the approach of Bai et al [23]. Bullet-shaped crystals in chains have variable overlap in the two-dimensional images.…”

“…Recent development of micromagnetic methods enables quantitative calculations of the magnetic properties of magnetosome chains with changing morphological parameters [20,21], i.e. particle size, particle spacing, particle elongation and chain structure (straight chain, collapsed chain, and ringshaped chain) [22][23][24][25][26][27][28]. However, the majority of simulation work relies on approximated chain models, while micromagnetic models with realistic chains are scarce, especially for the rarely simulated bullet-shaped magnetosome chains.…”

Microbial biosignatures in ancient deep‐sea hydrothermal sulfides

“…These features include narrow size/shape distributions, diagnostic crystal morphologies (e.g., bullet‐shaped, elongated prismatic), an arrangement of crystals in chains, crystallographic perfection, major and trace element chemical purity, high Fe(II)/Fe(III) ratios, and isotopic fingerprints (e.g., Amor et al, 2015, 2016; Lam et al, 2010; Thomas‐Keprta et al, 2000). Greigite magnetosomes show distinctly different magnetic properties than abiotic greigite (Bai et al, 2022). Still, greigite magnetosomes exhibit more crystallographic defects and chemical impurities than magnetite magnetosomes, making their identification more difficult (Kopp & Kirschvink, 2008).…”

“…Consequently, Fe(III) ratios, and isotopic fingerprints (e.g., Amor et al, 2015Amor et al, , 2016Lam et al, 2010;Thomas-Keprta et al, 2000). Greigite magnetosomes show distinctly different magnetic properties than abiotic greigite (Bai et al, 2022). Still, greigite magnetosomes exhibit more crystallographic defects and chemical impurities than magnetite magnetosomes, making their identification more difficult (Kopp & Kirschvink, 2008).…”