ARTICLE

THE PHOTOSYNTHETIC APPARATUS OF RHODOSPIRILLUM MOLISCHIANUM

Sarah P. Gibbs ¹, W. R. Sistrom ¹, and Patricia B. Worden ¹

¹ From the Department of Bacteriology, University of Edinburgh, Edinburgh, Scotland, the Department of Biology, University of Oregon, Eugene, and The Biological Laboratories, Harvard University, Cambridge, Massachusetts.

Dr. Gibbs' present address is Division of Biological Sciences, McGill University, Montreal, Canada. Dr. Worden's present address is Department of Connective Tissue Research, The Retina Foundation, Boston

By varying the light intensity and temperature during growth it is possible to obtain cultures of Rhodospirillum molischianum in which the specific bacteriochlorophyll contents differ by as much as fivefold. We used such cultures to compare the changes in the electron microscopic appearance of the cells with the changes in the amount and bacteriochlorophyll content of chromatophore material isolated from cell extracts. The cells contained a variable number of internal membranes which are invaginations of the cell membrane. The shape, size, number, and arrangement of the infoldings varied as the specific bacteriochlorophyll content of the cells changed. In cells with little bacteriochlorophyll, the invaginations were mostly tubular. In cells with larger amounts of bacteriochlorophyll, the invaginations were disc-shaped and the discs were appressed together in stacks of 2 to 10 discs each. Variations in the number of discs per stack could be accounted for by a simple statistical model. The average area per disc increased with increasing bacteriochlorophyll content. Quantitative estimations of the relative volumes occupied by membranes in cells with four different bacteriochlorophyll contents showed that the amount of internal membrane alone had no direct relationship with the bacteriochlorophyll content of the cells; however, the total amount of membrane (cell membrane plus internal membrane) was directly proportional to the bacteriochlorophyll content. The specific bacteriochlorophyll content of isolated chromatophore material was proportional to the bacteriochlorophyll content of whole cells; the total amount of chromatophore material was independent of the bacteriochlorophyll content of whole cells. Several possible explanations of this paradoxical discrepancy between the electron microscope observations and the analytical results are discussed.

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This article has been cited by other articles:

• Sojka, G. A., Baccarini, A., Gest, H. (1969). Energy Flux and Membrane Synthesis in Photosynthetic Bacteria. Science 166: 113-115 [Abstract]  
• Eakin, R. M. (1965). Evolution of Photoreceptors. Cold Spring Harb Symp Quant Biol 30: 363-370 [Abstract]  

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