STRUCTURE OF PHOTOSYNTHETIC BACTERIA 103 



THE INTERNAL ORGANIZATION OF THE CHLOROBIUM CELL 



Fine structure studies on green bacteria have so far been very lim- 

 ited, Vatter and Wolfe (4) published one micrograph of a thin section of 

 Chlorobium limicola. The cytoplasm contained numerous very electron- 

 dense bodies, which the authors equated with chromatophores, despite 

 the fact that these bodies showed no resemblances to the vesicular 

 elements of purple bacteria. They could perhaps be more reasonably 

 interpreted as deposits of polyphosphate. Bergeron and Fuller (24) 

 have published a micrograph of a thin section of Chlorobium thiosul- 

 fatophilum, which shows, according to the authors, that the fine struc- 

 ture of this bacterium is essentially indistinguishable from that of 

 an ordinary nonphotosynthetic true bacterium such as £s c/zencMa coZ/. 

 Bergeron and Fuller (24) also made the first detailed study of the lo- 

 cation of the pigment system in cell-free extracts of a green bacterium. 

 They broke the cells of C. thiosulfatophilum by a highly comminutive 

 treatment: sonic oscillation of cells suspended with a fine synthetic 

 sapphire abrasive. The bulk of the pigment system in such extracts 

 was associated with particles about 150 A in diameter, difficultly 

 separable from ribosomes, and having a molecular weight of approxi- 

 mately 1,5 million. Since the most conspicuous cytoplasmic elements 

 observable in their thin sections were also particles with an approxi- 

 mate diameter of 150 A, Bergeron and Fuller assumed the identity of 

 their isolated "holochrome" with these cellular elements. 



We have recently collaborated with Dr. Norbert Pfennig on a study 

 of the fine structure of five strains of Chlorobium. The strains in- 

 cluded representatives of the limicola 3nA thiosulfatophilum physiologi- 

 cal types, and also of the two sub-groups which can be distinguished on 

 the basis of the chlorobium chlorophyll that they contain. They are thus 

 representative of the group as a whole. 



Although our work on these organisms is still in progress, the find- 

 ings to date, with respect both to the structure of the intact cell and to 

 the properties of the pigment system in extracts, differ in major re- 

 spects from the findings of Bergeron and Fuller (24). The green bac- 

 teria that we have examined all share a highly distinctive and complex 

 fine structure, quite unlike that found in purple bacteria— or, indeed, 

 in any other type of bacterium so far studied by modern techniques of 

 electron microscopy. Thin sectionsof three different strains are shown 

 in Figs, 13-15. 



The cell wall has the double- layered structure characteristic of 

 Gram-negative bacteria, with a thin, sharply defined inner layer, and 

 a thicker, less dense outer layer. In some strains, it is ornamented by 

 rod-shaped extensions about 300 A wide, with a helically patterned 

 surface structure (Figs. 13 and 14); the presence of these elements on 

 the wall seems to be characteristic of strains that give a slimy type of 

 growth in liquid media. Underlying the wall is a complex membrane 



