STRUCTURE OF PHOTOSYNTHETIC BACTERIA 97 



of Vatter and Wolfe (4), vesicles are not completely absent from aero- 

 bically grown depigmented cells (Figs. 3 and?), although they are rare, 

 particularly in R. rubrum. 



These cytological studies lead us to the following interpretation of 

 the organization of the photosynthetic apparatus in the two species so 

 far discussed. The photosynthetic pigment system is incorporated into 

 a continuous unit membrane, which arises from the cytoplasmic mem- 

 brane and can intrude into the cytoplasm to a greater or lesser extent, 

 depending on the specific pigment content of the cell. Since structurally 

 indistinguishable membranous intrusions occur in aerobically grown 

 cells with a negligible pigment content, these intrusions are not nec- 

 essarily always associated with the presence of a functional photo- 

 synthetic apparatus. However, recent fine structure studies have shown 

 that a variety of membranous intrusions derived from the cytoplasmic 

 membrane may occur in nonphotosynthetic, aerobic bacteria (19). The 

 "simple intrusives" discovered by Murray (19) in the nonphotosynthet- 

 ic organism Spirillum serpens are quite similar in appearance and 

 intracellular position to the sparse, peripheral vesicles characteristic 

 of R. rubrum and Rkodopseudomonas spheroides grown aerobically in 

 the dark or anaerobically at high light intensities. A general functional 

 interpretation of these intrusions in aerobic and photosynthetic bac- 

 teria has been offered by Stanier (20). 



On the basisof a recent study of the fine structure of Rho do spirillum 

 molischianum, Giesbrecht and Drews (21) have proposed a very similar 

 interpretation of the organization of the photosynthetic apparatus in 

 this species. In cells sectioned after osmotic lysis, the physical con- 

 nection between the characteristic lamellar bundles and the cytoplasmic 

 membrane was clearly evident. 



THE FINE STRUCTURE OF SOME NEWLY ISOLATED 

 PURPLE SULFUR BACTERIA 



Thus far, fine structure studies on the sulfur purple bacteria have 

 been confined to a single strain, Chromatium strain D, the only 

 representative of this group which has been generally available in pure 

 culture. Recently, Dr. Norbert Pfennig has succeeded for the first 

 time in isolating and growing in pure culture a number of other types, 

 including Chromatium okenii and Thio spirillum jenense (22). Through 

 his kindness, we have been able to examine the fine structure of some 

 of the strains in his collection. C. okenii and T. jenense were of 

 particular interest, since their cells are much larger than those of 

 any other photosynthetic bacteria, with a volume about a thousand 

 times that of the cell of Rkodopseudomonas spheroides or R. rubrum. 

 Figs. 8 and 9 show typical thin sections of these two large purple sul- 



