84 THE BACTERIAL PHOTOCHEMICAL APPARATUS 



Fig. 10. Electron micrograph of a thin section of Chromatiuni strain D grown 

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



A Striking change in the chlorophyll to protein ratio of the cells can 

 be seen. At low light intensities the amount of chlorophyll per mg pro- 

 tein doubles. These data are similar to those obtained by Cohen- 

 Bazire et al. (18), Sistrom (23), and Lascelles (24), who noted an in- 

 crease in the chlorophyll content of cells of Rhodopseudomonas 

 spheroides when grown at low light intensities. Of equal interest is 

 the rather striking increase in total lipids in cells grown at low light 

 intensity. This increase may represent structural lipids associated 

 with the chlorophyll-bearing structure. 



Although Chromatium strain D has always appeared to contain chro- 

 matophores at all stages of growth, electron microscopy of cells 

 exhibiting spectral and chemical differences was undertaken to ascer- 

 tain if the changes in the spectrum and chlorophyll-protein ratios 

 might be reflected in the structure of the photochemical apparatus. 



Fig, 5 illustrates the appearance in electron micrographs of Chro- 

 matium cells grown under conditions of low light intensity. The pres- 

 ence of chromatophores (-300 A in diameter) throughout the cell is in 

 conformity with the observations of other investigators. In contrast 

 to this, cells grown under conditions of high light intensity (7000 foot- 

 candles incident light) show marked structural alterations (Figs, 8 and 



