Amor Matthieu, Wan Juan, Egli Ramon, Carlut Julie, Gatel Christophe, Andersen Ingrid Marie, Snoeck Etienne, Komeili Arash
Department of Plant and Microbial Biology, University of California, Berkeley, CA, USA.
Aix-Marseille Université, CEA, CNRS, BIAM, Saint-Paul-lez-Durance, France.
J Geophys Res Solid Earth. 2022 Jan;127(1). doi: 10.1029/2021jb023239. Epub 2021 Dec 28.
Magnetotactic bacteria (MTB) produce single-stranded or multi-stranded chains of magnetic nanoparticles that contribute to the magnetization of sediments and rocks. Their magnetic fingerprint can be detected in ancient geological samples and serve as a unique biosignature of microbial life. However, some fossilized assemblages bear contradictory signatures pointing to magnetic components that have distinct origin(s). Here, using micromagnetic simulations and mutant MTB producing looped magnetosome chains, we demonstrate that the observed magnetofossil fingerprints are produced by a mixture of single-stranded and multi-stranded chains, and that diagenetically induced chain collapse, if occurring, must preserve the strong uniaxial anisotropy of native chains. This anisotropy is the key factor for distinguishing magnetofossils from other populations of natural magnetite particles, including those with similar individual crystal characteristics. Furthermore, the detailed properties of magnetofossil signatures depend on the proportion of equant and elongated magnetosomes, as well as on the relative abundances of single-stranded and multi-stranded chains. This work has important paleoclimatic, paleontological, and phylogenetic implications, as it provides reference data to differentiate distinct MTB lineages according to their chain and magnetosome morphologies, which will enable the tracking of the evolution of some of the most ancient biomineralizing organisms in a time-resolved manner. It also enables a more accurate discrimination of different sources of magnetite particles, which is pivotal for gaining better environmental and relative paleointensity reconstructions from sedimentary records.
趋磁细菌（MTB）产生单链或多链的磁性纳米颗粒，这些颗粒有助于沉积物和岩石的磁化。它们的磁指纹可以在古老的地质样本中被检测到，并作为微生物生命的独特生物特征。然而，一些化石组合具有相互矛盾的特征，表明磁性成分有不同的来源。在这里，我们使用微磁模拟以及产生环状磁小体链的突变趋磁细菌，证明观察到的磁化石指纹是由单链和多链的混合物产生的，并且如果发生成岩作用导致的链塌陷，必须保留天然链的强单轴各向异性。这种各向异性是区分磁化石与其他天然磁铁矿颗粒群体的关键因素，包括那些具有相似单晶特征的颗粒。此外，磁化石特征的详细性质取决于等轴状和拉长状磁小体的比例，以及单链和多链的相对丰度。这项工作具有重要的古气候、古生物学和系统发育学意义，因为它提供了参考数据，以便根据趋磁细菌的链和磁小体形态区分不同的趋磁细菌谱系，这将能够以时间分辨的方式追踪一些最古老的生物矿化生物体的进化。它还能够更准确地区分磁铁矿颗粒的不同来源，这对于从沉积记录中获得更好的环境和相对古强度重建至关重要。
