Tracking the emergence and evolution of magnetotactic bacteria from the fossil record of magnetite – BIOMAG

Magnetotactic bacteria perform biomineralization of intracellular magnetite (Fe3O4) nanoparticles. Although they may be among the earliest microorganisms capable of biomineralization on Earth, identifying their activity in ancient sedimentary rocks remains challenging because of the lack of reliable biosignatures. Recently, it has been demonstrated that molybdenum possesses a strong affinity for magnetite produced by magnetotactic bacteria relative to abiotic magnetite samples. Such molybdenum enrichement in biological magnetite was proposed to be generated by molybdenum-dependent metabolic reactions that are necessary for energy production and magnetite formation in the bacteria. Accordingly, molybdenum is likely to undergo unique isotopic fractionations during incorporation into biological magnetite. The present project aims at establishing molybdenum as a reliable tool for the identification of the fossil remains of magnetotactic bacteria in ancient geological samples. In a first round of experiments, the isotope signatures of molybdenum in magnetite produced either by magnetotactic bacteria or from abiotic reactions will be calibrated. Their potential for surviving diagenetic and fossilization processes will then be assessed from experimental fossilization. Finally, key geological samples will be analyzed to determine the biological or abiotic origin of the magnetite crystals they contain from their chemical and isotopic molybdenum signatures.