Bacterial Intracellular Biomineralization Can Form Magnetic Nanofossils, Study Finds

In 1963, Italian scholar Bellini first discovered susceptibility bacteria in freshwater and published research results, but they did not attract attention. In 1975, when an American doctor of microbiology studied spirochetes in seafloor sludge, he accidentally found that this type of microorganism that can swim along the applied magnetic field and synthesize nanoscale ferric oxide crystal particles arranged in chains in the cells. He named them magnetotactic bacteria. This, however, attracted the attention of scientists and opened the prelude to magnetotactic bacteria research. In 1986, two groups in the United States and Germany discovered magnetic nanofossils–magnetosome fossils left after the death of magnetotactic bacteria in marine sediments, which directly prompted Earth scientists (especially researchers in the fields of paleomagnetism and marine magnetism) to join the study of magnetotactic bacteria and magnetosome fossils. In 1996, NASA scientists said the discovery of nanoscale magnetite particles suspected of magnetosome fossils in the Martian meteorite ALH84001, which once again set off an upsurge in the search for magnetosome fossils from ancient sediments and rocks for early life, paleoenvironment, and paleomagnetic research.

After many years of research, scholars in the fields of life sciences, geoscience, and material science have carried out research on the ecological distribution and species diversity of magnetotactic bacteria, magnetosome biomineralization processes and their molecular mechanisms, magnetosome fossil recognition and ancient geomagnetic applications, magnetosome bionics, and nanomedicine applications. The general path of magnetosome synthesis and multiple related genes and their functions have been clarified, and many rock magnetism, mineralogy and crystallography parameters have been proposed to identify magnetosome fossils.

However, the knowledge of the fine processes of magnetosome biomineralization (especially inorganic processes of crystal growth and magnetic changes) and their diversity is still insufficient in the academic community. It is still challenging to identify magnetosome fossils from geological records and use them to carry out paleomagnetic, paleoenvironmental and early life studies. The main reasons are: (1) the preliminary study of magnetosome crystal growth mechanism is only carried out in a few laboratory-cultivable magnetotactic bacteria, restricting the comprehensive understanding of magnetotactic bacterial magnetosome diversity and its biomineralization mechanism; (2) the magnetosome fossil recognition standards and methods established based on the study of a few magnetotactic bacteria are limited, and even some standards are not accurate, restricting the progress of finding and identifying magnetosome fossils, perfecting the original recognition standards and establishing new magnetosome fossil recognition standards is imminent; (3) the lack of systematic microbial molecular ecology, electron microscopy and nanomagnetism studies leads to the lack of establishing the internal relationship of "magnetotactic bacterial species-magnetosome biomineralization-magnetosome magnetic properties", resulting in that the current academic community cannot obtain the biological and ecological information of magnetotactic bacteria during the geological history from the magnetic properties and crystal structure characteristics of magnetosome fossils.

In response to the above problems, in recent years, the research team of the Geomagnetic Field and Biosphere Evolution Discipline Group of the Institute of Geology and Geophysics, Chinese Academy of Sciences, in conjunction with the Institute of Physics, Chinese Academy of Sciences, Paris Sixth University, France, and National University of Australia, carried out a multidisciplinary study of biogeomagnetism and geobiology on magnetotactic bacteria cultured in the environment. Researchers have established a new technology of "fluorescence-electron microscopy" (FISH-Sem and FISH-Tem), which combines the fluorescence microscope observation signal for the identification of magnetotactic bacteria and the electron microscope observation signal for the magnetosome structure observation. For the first time, the species identification and biomineralization research of uncultured magnetotactic bacteria has been realized at the single-cell level. Using this technology, researchers have studied lakes in Beijing and surrounding areas (such as Miyun Reservoir and Beihai), lakes in Xi'an and surrounding areas (such as Weiyang Lake, Moat, and Xianyang Lake), as well as the brackish water and marine environment along the coast of Qinhuangdao, Hebei, (Such as Tanghe, Shihe Estuary and Qilihai, etc.) and more than 20 new species of magnetotactic bacteria have been discovered in four categories; Synchrotron radiation technology was applied to carry out a comprehensive study from micronanometer size to atomic level for one cell of each magnetotactic bacterium.

Recently, researchers have studied the cell morphology, chemical composition and the crystal growth process of magnetosome of Magnetotactic bacteria WYHR-1 from the sediments of Weiyang Lake in Xi'an, and found that magnetotactic bacteria can mineralize and synthesize in cells Magnetite (Fe3O4) particles (also called magnetosomes) with "nano-size and unique crystal structure". The crystal growth process and crystal forms of magnetosomes are diverse, but they are unique in the same group or the same kind of magnetotactic bacteria.

Based on the above studies, the researchers proposed that the biomineralization patterns of magnetosomes (at least in terms of crystal growth) are diverse, but the crystal growth process is strictly regulated by different magnetotactic bacteria groups or strains/strains at the genetic level. The crystal form is therefore specific. Magnetotactic bacteria magnetosomes are potential magnetic nanofossils. In future research, the morphological characteristics of magnetosomal fossils in sediments and their corresponding magnetic properties can be analyzed to obtain information on the groups or types of ancient magnetotactic bacteria. In order to carry out research on "paleomagnetotactic bacteria, paleoenvironment and paleomagnetic field" at the same time.