Epsilon-Fe ₂ O ₃ is a novel intermediate for magnetite biosynthesis in magnetotactic bacteria

Abstract Background Natural biological magnetite nanoparticles are widely distributed from microorganisms to humans. It is found to be very important in organisms, especially in navigation. Moreover, purified magnetite nanoparticles also have potential applications in bioengineering and biomedicine. Magnetotactic bacteria (MTB) is considered one of the most abundant species around the world which can form intracellular membrane enveloped magnetic nanoparticles, referred to as magnetosomes. To our knowledge, the biomineralization of magnetosome in MTB involves a serious of genes located on a large unstable genomic region named magnetosome island, which specially exists in MTB. The magnetite core of magnetosome formed via a Fe (III) ion intermediates, for instance, α -Fe ₂ O ₃ and ferrihydrite. Though the biosynthesis of magnetosome represents a general biomineralization mechanism of biogenic magnetite, knowledge of magnetosome biosynthesis and biomineralization remains very limited. Method Cells used in this study were cultured in a 7.5-L bioreactor, samples for intermediate capture were taken each certain time interval after the generation of magnetosome biosynthesis condition. High-resolution transmission electron microscopy were used to analyze the detailed structure of magnetosomes. The parameters of the crystal structures were obtained by Fast Fourier Transform analyses. Results In this study, we identified a novel intermediate phase, ε -Fe ₂ O ₃ , during the magnetite maturation process in MTB via kinetic analysis. Unlike α -Fe ₂ O ₃ , which has been reported as a precursor during magnetosome biosynthesis in MTB before, ε -Fe ₂ O ₃ , due to its thermal instability, is a rare phase with scarce natural abundance. This finding confirmed that ε -Fe ₂ O ₃ is an important novel intermediate during the biomineralization of magnetosome in MTB, and shed new light on the magnetosome biosynthesis pathway.