Electron microscopy of chromatophores of Rhodopseudomonas spheroides.

Gibson, K. D. (St. Mary's Hospital Medical School, London, England). Electron microscopy of Rhodopseudomonas spheroides. J. Bacteriol. 90:1059-1072. 1965.-Fixed and stained chromatophores and whole cells of anaerobically grown Rhodopseudomonas spheroides were examined in thin sections in the electron microscope. Both purified chromatophores and intracellular membrane-bound vesicles had exactly the same appearance, namely that of spheres or ellipsoids with a thin electron-dense shell surrounding an electron-lucent interior. The distribution of diameters in the two types of structure was also found to be the same, and was compatible with a normal distribution, with a mean of 570 A and a standard deviation 40 A. Negatively stained chromatophores appeared like discs or collapsed spheres. The presence of invaginations of the cytoplasmic membrane in this species was confirmed, and a new structure resembling a twin chromatophore was observed. The bearing of these results on theories of the origin of chromatophores is discussed, and it is concluded that they offer some support for each one of the three main theories about the origin of particulate organelles.