Pigment Carrying Structures of the Photosynthetic Non-sulphur Purple Bacterium Rhodopseudomonas Spheroides.

As observed under the electron microscope (6), aqueous extracts of photosynthetic bacteria contain grana-like structures; most probably, these organelles are built up of lamellae. Pardee, Schachman and Stanier (5) showed that the colored sediment obtained by centrifugation of aqueous extracts of Rhodospirillum rubrum consisted of the above-mentioned granalike structures. Niklowitz and Drews (4) prepared ultra-thin sections of Rhodospirillum rubrum. Electron microscopical examination revealed that this photosynthetic bacterium contains lamellated structures. This was confirmed by Elbers, Minnaert and Thomas (2). On the other hand, Vatter and Wolfe (9) observed spherical organelles packed throughout the bacterial cell. These organelles were considered to be chromatophores. Vatter and Wolfe (9, 10) stated that light is essential for the formation of these chromatophores. The latter authors studied a number of photosynthetic bacteria, among which was Rhodopseudomonas spheroides. Thus, the results seem to be conflicting. A private discussion, however, revealed that the age of the bacteria may be responsible for this discrepancy. Vatter and Wolfe used bacteria only a few days old, whereas Elbers et al studied 7to 10-day-old cultures which were still in a photosynthetically active state. Goedheer (3) studied polarization of bacteriochlorophyll fluorescence in Rhodospirillum rubrum and Chromatium. Since, be it only to a relatively small degree, polarization was found to occur, it was concluded that the pigment molecules are preferentially oriented. This conclusion favors the conception of the occurrence of flat lamellae rather than that of vesicles. In any case, if the bacteriochlorophyll molecules were attached to the surface of vesicles, these structures should be flattened in a preferential plane. It would be interesting to study polarization of bacteriochlorophyll in both young and aged cultures. Though it seems likely, evidence that bacteriochlorophyll is connected with lamellar structures in some way or another is so far lacking. Working with Hibiscus rosa sinensis, Thomas, Post and Vertregt (8) obtained the indication that, in the living cell, the occurrence of chlorophyll is restricted to the grana lamellae. They used the Molisch reaction, i.e. silver nitrate reduction in the presence of excited chlorophyll, as a tool for localization of this pigment. However, because of the small dimensions of the bacterial photosynthetic apparatus, the silver nitrate