Electron Microscope Autoradiography of Bacteria Labeled with Iodine-125

The low-energy extranuclear electrons emitted by iodine-125 can be used for electron microscope autoradiography with results comparable to those obtained with tritium. Autoradiographs of tritium-labeled bacteria showed that 71 percent of all reacted grains localized on the cell. This figure was 86 percent when I(125)-labeled bacteria were used.