92 THE BACTERIAL PHOTOCHEMICAL APPARATUS 



TABLE 1. 



Bacteria chlorophyll content of no nsul fur purple bacteria growing 

 under different environmental conditions 



Rhodospirillmn rubrum 



Photosynthetic growth at Chlorophyll content of cells, /Ug/mg 



light intensity of: cellular protein. 



50 foot-candles 25.0 



2000 foot-candles 10.2 



6000 foot-candles 5.6 



Respiratory growth conditions: 



Full aeration 0.2 



Full aeration, then limiting oxygen for 



3 hr. 3.3 



Rhodopseudomonas spheroides 



Photosynthetic growth at 

 light intensity of: 



50 foot-candles 66 



9500 foot-candles 5.9 



Aerobic growth 0.14 



classical profile of a photosynthetically grown cell with a vesicle- 

 filled cytoplasmic region, as first described for these two species by 

 Vatter and Wolfe (4), is characteristic only for cells which have been 

 grown at very low light intensities, and therefore have a high specific 

 chlorophyll content (Figs. 1 and 5), In sections of cells grown at pro- 

 gressively higher light intensities, the abundance of vesicles declines 

 systematically, and their location in the cell becomes increasingly 

 peripheral. In cells grown anaerobically at light intensities of 5000 

 foot-candles or higher, most of the cytoplasmic region in sections is 

 filled with a dense array of ribosomes, and the relatively rare 

 membrane-bounded vesicles occur exclusively in the neighborhood of 

 the cytoplasmic membrane (Figs, 2 and 6), Two other important struc- 

 tural features become evident in such cells. Firstly, the typical unit 

 membrane which bounds each vesicle is identical in thickness and 

 fine structure to the cytoplasmic membrane. Secondly, the membrane 

 that encloses a vesicle is sometimes sectioned in a plane that reveals 

 its continuity with adjacent regions of the cytoplasmic membrane. The 

 central, transparent area of such vesicles opens through a narrow 

 aperture into the space that lies between wall and membrane, and is 

 consequently external to the cytoplasm proper. Contrary to the report 



