BACTERIAL PHOTOSYNTHESIS 203 



DISCUSSION 

 D. Waugh, J. A. Bergeron, A. C. Giese, M. V. Edds, Jr. 



Dr. Waugh (Massachusetts Institute of Technology): The properties 

 found for the chroinatophores themselves prompt me to ask about the physical 

 and chemical properties of the protein component alone. 



Dr. Bergeron: Our knowledge hasn't advanced sufficientlv for such a 

 study. However, the results of our initial attempts to obtain subunits by lysing 

 the chromatophores with disulfide-cleaving agents have been promising. If 

 we succeed in obtaining preparations which fulfill the criteria for subunits, 

 then we will be in a better position to study the protein itself. 



Dr. Giese (Stanford University): Does the proportion of one pigment to 

 another in the chromatophore vary with the quality of the light, or with other 

 conditions under which the culture is grown? 



Dr. Bergeron: As you know, the colored-carotenoid:bacteriochlorophyll 

 ratio can vary considerably. Since Stanier's evidence (1958) indicates that 

 under certain conditions colorless precursors are transformed in situ, it is con- 

 ceivable that there is a fixed ratio between bacteriochlorophyll and the C40 

 compounds, without specifying the degree of unsaturation. We believe that 

 the protein-bacteriochlorophyll relationship probably sets a limiting value, with 

 local conditions determining the kind and amount of carotenoids which are 

 built into the chromatophore. 



Dr. Edds (Brown University): Are you able to tell us anything about the 

 development of chromatophores? 



Dr. Bergeron: We know very little about the development of bacterial 

 chromatophores. There is the evidence that chromatophores form de novo in 

 cells of Rhodospirillum nihrum when these organisms are induced to photo- 

 synthesize after a period of total dependence upon aerobic metabolism in the 

 dark. We cannot perform similar experiments with Chromatium, which is an 

 obligate anaerobic phototroph. 



If chromatophores can appear in a cytoplasm which has been devoid of 

 these structures, then we can assume either that the new chromatophores are 

 derived by proliferation from other structures, such as the plasma membrane, 

 or the larger vesicles, or that the chromatophores are the morphological con- 

 sequence of the "homing instinct" of molecular subunits. Although, as oui 

 model indicates, we favor the idea of the subunit, it should be pointed out 

 that immunochemical data have been employed by Newton (1958) to infer a 

 specific relationship between the surface of the organism and the chromato- 

 phores, and we have observed evaginations from the larger vesicles. These 

 evaginations, if severed, would be morphologically indistinguishable from the 

 chromatophores. 



