STRUCTURE OF PHOTOSYNTHETIC SULFUR BACTERIA 85 



Fig. 11. Electron micrograph of a thin section of Chromatiutn strain D grown 

 at 7000 foot candles of incident light. Bar equals Ifl. (See text for details). 



9). Although chromatophores are still present, an intracytoplasmic 

 membrane system can also be observed. These intracytoplasmic mem- 

 branes are observed most frequently in the peripheral areas of the 

 cells. Close inspection of the plates reveal that these membranes are 

 paired. Each membrane (~ 100 A thick) corresponds to a unit membrane, 

 but this has not yet been clearly demonstrated by high resolution 

 studies. Fig. 10 is another micrograph of a cell grown under conditions 

 of high light intensity. It appears that chromatophore-like structures 

 are formed at the terminal ends of the invaginated paired membranes 

 (see arrow). Occasionally, cells groAvn under conditions of high light 

 intensity appear to have the intracellular membranes organized in a 

 lamellar system (Fig. 11). 



It was observed that when cells are grown under conditions which 

 induce the formation of intracellular membranes and cell-free ex-- 

 tracts prepared, the majority of the pigment-bearing particulate 

 material sediments at relatively low centrifugal forces as compared 

 to the situation encountered with "normal" cells. 



