Electron microscope study of the interaction of epibiontic bacteria with Chromatium minus in natural habitats

Epibiontic cells on the surface of the photosynthetic purple sulfur bacterium Chromatium minus, collected several times during the year from 3 different Spanish lakes, were examined using scanning and transmission electron microscopy. The cells attached to the C. minus cell wall by an electron-dense pad, but did not enter the cell. They were ovoidal (about 0.6 Μm wide) when free, and slightly curved rods (0.3×0.6 Μm) when undergoing division. Division only occurred when cells remained attached to Chromatium. A septum was formed, resulting in 2 or 3 curved rods surrounded by a common capsule. Detached daughter cells became ovoidal. The host ultrastructure changed as a result of epibiontic attachment, showing symptoms of cellular degradation. Simultaneously, plaques could be detected on cell lawns formed spontaneously upon cell sedimentation from field samples.