Current view of iron biomineralization in magnetotactic bacteria.

Biomineralization is the process of mineral formation by living organisms. One notable example of these organisms is magnetotactic bacteria (MTB). MTB are Gram-negative bacteria that can biomineralize iron into magnetic nanoparticles. This ability allows these aquatic microorganisms to orient themselves according to the geomagnetic field. The biomineralization process takes place in a specialized sub-cellular membranous organelle, the magnetosome. The magnetosome contains a defined set of magnetosome-associated proteins (MAPs) that controls the biomineralization environment, including iron concentration, redox, and pH. Magnetite formation is subjected to a tight regulation within the magnetosome that affects the nanoparticle nucleation, size, and shape, leading to well-defined magnetic properties. The formed magnetite nanoparticles have unique characteristics of a stable, single magnetic domain with narrow size distribution and high crystalline structures, which turned MTB into the subject of interest in multidisciplinary research. This graphical review provides a current overview of iron biomineralization in magnetotactic bacteria, focusing on Alphaproteobacteria. To better understand this complex mechanism, we present the four main steps and the main MAPs participating in the process of magnetosome formation.