Keylab Experimentelle Biogeochemie

Soft X-ray scanning transmission X-ray microscopy (STXM) was used to measure the Fe L_{2, 3} X-ray magnetic circular dichroism (XMCD) signal from individual, 30 nm diameter magnetosomes in a magnetotactic bacterium, specifically the marine vibrio strain MV-1. The Fe L_{2, 3} spectra recorded with circularly polarized X-rays from an elliptically polarizing undulator were very similar in shape and magnitude to those of fully saturated magnetite (Fe₃O₄). As previously determined by other techniques, our results show that the magnetic moments of individual magnetosomes arranged in linear chains in intact cells of strain MV-1 are all oriented in the same direction. The magnitude of the XMCD signal averaged over a chain of 9 magnetosomes in one cell is similar to that of single crystal magnetite. The spectral shape is slightly different, and indicates that magnetosomes have excess Fe^(II), as noted in previous bulk studies of biogenic magnetite. To our knowledge, this is the first measurement of the XMCD of individual magnetosomes in magnetotactic bacteria.