Although magnetoreception has been intensively studied in recent years and is one of the most amazing achievements in nature, the exact mechanism of magnetosome formation is still not fully understood. Several models have been proposed, including direct precipitation of magnetite or greigite from the cytoplasm, transformation of membrane-bound iron sulfides into magnetite, or more complicated processes involving the transport of iron and sulfur ions through the magnetosome membrane.
To shed light on the formation mechanism of magnetosomes, researchers from the Technical University of Munich (TUM) have studied the magnetotactic bacterium Magnetospirillum magneticum AMB-1 using synchrotron X-ray microscopy and spectroscopy at the Helmholtz-Zentrum Berlin (HZB). The combination of these techniques allowed them to analyze the elemental composition and magnetic properties of the magnetosomes with high spatial resolution.
The results show that the magnetosomes in Magnetospirillum magneticum AMB-1 are composed of a magnetite core surrounded by a thin membrane. The core contains approximately 50% iron and 50% oxygen, which are arranged in an inverse spinel structure. The membrane is composed of a mixture of lipids, proteins, and carbohydrates, and it is approximately 5 nm thick.
The researchers also found that the magnetosomes are formed by the direct precipitation of magnetite from the cytoplasm. This process is initiated by the accumulation of iron and oxygen ions inside the magnetosome membrane. The ions then react to form magnetite crystals, which grow until they reach their final size.
These findings provide new insights into the formation mechanism of magnetosomes and contribute to our understanding of how magnetotactic bacteria orient and navigate along the Earth's magnetic field lines.
