TEM Image (IMAGE) Proceedings of the National Academy of Sciences Caption This is a TEM image of cells of magnetotactic bacteria aligned in a magnetic field at 140 millitesla. The dark crystals are made of biological magnetite. Credit PNAS Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.