Electron microscope study of the interaction of epibiontic bacteria withChromatium minus in natural habitats.

Epibiontic cells on the surface of the photosynthetic purple sulfur bacteriumChromatium minus, collected several times during the year from 3 different Spanish lakes, were examined using scanning and transmission electron microscopy. The cells attached to theC. minus cell wall by an electron-dense pad, but did not enter the cell. They were ovoidal (about 0.6Μm wide) when free, and slightly curved rods (0.3×0.6Μm) when undergoing division. Division only occurred when cells remained attached toChromatium. 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.