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

Natural biological magnetitenanoparticles are widely distributed from microorganisms to humans. It is found to be very important in organisms, especially in navigation. Moreover, purified magnetitenanoparticles 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 biomineralizationof magnetosomein MTB involves a serious of genes located on a large unstable genomic region named magnetosomeisland, which specially exists in MTB. The magnetitecore of magnetosomeformed via a Fe (III) ion intermediates, for instance, α-Fe2O3 and ferrihydrite. Though the biosynthesisof magnetosomerepresents a general biomineralizationmechanism of biogenic magnetite, knowledge of magnetosome biosynthesisand biomineralizationremains very limited. 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 biosynthesiscondition. 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. In this study, we identified a novel intermediate phase, e-Fe2O3, during the magnetitematuration process in MTB via kinetic analysis. Unlike α-Fe2O3, which has been reported as a precursor during magnetosome biosynthesisin MTB before, e-Fe2O3, due to its thermal instability, is a rare phase with scarce natural abundance. This finding confirmed that e-Fe2O3 is an important novel intermediate during the biomineralizationof magnetosomein MTB, and shed new light on the magnetosome biosynthesispathway.