Magnetotactic bacteria are able to align their swimming direction to the geomagnetic field lines because they possess a magnetic moment. These bacteria biomineralize magnetic nanoparticles, magnetite or greigite, inside a membrane. The membrane + nanoparticle set is known as magnetosome and intracellular magnetosomes are disposed in a linear chain. Cytoskeleton-like filaments are resposible for the mechanical stability of this chain. The genes responsible for the magnetosome membrane and for the cytoskeleton proteins have been largely studied: the mam genes. The magnetosome chain also confers to the bacterial body a magnetic moment that can be measured through different physical techniques. Because of their response to magnetic field inversions, magnetotactic bacteria are good models to study bacterial motion. Theoretical and experimental studies show that magnetotactic bacteria swim following a trajectory similar to cylindrical helix. Magnetotactic microorganisms have been observed avoiding regions with UV or violet-blue light of high intensity. If the intensity is lower, magnetotactic microorganims show photokinesis, increasing their velocity in the presence of red light and decreasing their velocity in the presence of green light, both relative to the velocity with blue light.
Part of the book: Microorganisms
Biomineralization in the microbial realm usually gives origin to finely structured inorganic nanomaterials. Perhaps, one of the most elegant bioinorganic processes found in nature is the iron biomineralization into magnetosomes, which is performed by magnetotactic bacteria. A magnetosome gene cluster within the bacterial genome precisely regulates the mineral synthesis. The spread and evolution of this ability among bacteria are thought to be a 2,7-billion-year process mediated by horizontal gene transfers. The produced magnetite or greigite nanocrystals coated by a biological membrane have a narrow diameter dispersibility, a highly precise morphology, and a permanent magnetic dipole due to the molecular level control. Approaches inspired by this bacterial biomineralization mechanism can imitate some of the biogenic nanomagnets characteristics in the chemical synthesis of iron oxide nanoparticles. Thus, this chapter will give a concise overview of magnetosome synthesis’s main steps, some hypotheses about the evolution of magnetosomes’ biomineralization, and approaches used to mimic this biological phenomenon in vitro.
Part of the book: Materials at the Nanoscale