Biomineralization of ferrimagnetic greigite (Fe₃S₄) and iron pyrite (FeS₂) in a magnetotactic bacterium

Abstract

THE ability of magnetotactic bacteria to orientate and navigate along geomagnetic field lines is due to the controlled intracellular deposition of the iron oxide mineral, magnetite (Fe₃O₄)^1,2. The function and crystal chemical specificity of this mineral has been considered to be unique amongst the prokaryotes³. Moreover, the bacterial production of magnetite may represent a significant contribution to the natural remanent magnetism of sediments^4,5. Here we report, the intracellular biomineralization of single crystals of the ferrimagnetic iron sulphide, greigite (Fe₃S₄), in a multicellular magnetotactic bacterium common in brackish, sulphide-rich water and sediment. We show that these crystals are often aligned in chains and associated with single crystals of the non-magnetic mineral, iron pyrite (FeS₂). Our results have important implications for understanding biomineralization processes and magnetotaxis in micro-organisms inhabiting sulphidic environments. Furthermore, the biogenic production of magnetic iron sulphides should be considered as a possible source of remanent magnetization in sediments.