3o8 J. A. BERGERON AND R. C. FULLER 



description of photosynthetic phosphorylation in chloroplast preparations 

 by Arnon et a/. [2, 3] suppHed direct evidence for the idea of Emerson et al. 

 [17] that the role of light is to produce energy-rich bonds and also 

 strengthened the belief that the fundamental photochemical events are the 

 same in all photosynthetic organisms. Since that time considerable 

 information has accumulated about various properties of pigmented 

 preparations of photosynthetic bacteria (see papers in this symposium and 

 review by Frenkel [21]). However, only two organisms have been studied 

 in any real detail, R. rubrinn and Chromatium, the purple sulphur bac- 

 terium. The chromatophore of Chromatium represents the simplest level 

 of structural organization which is known to support photophosphoryla- 

 tion. We have considered the structure and function of this chromatophore 

 in some detail previously [6, 7]. This system provides the perspective for 

 a study which is in progress of the photochemical apparatus of the green 

 sulphur bacterium, Chlorobiiim thiosulfatophilum. In the interest of 

 clarity, the data, of several kinds, are considered at successive levels of 

 organization; the organism, the crude extracts, and the purified pigmented 

 component. 



Results 



THE ORGANISM 



The green sulphur bacterium, Chlurobiuni thiosulfatophilum, is a strict 

 anaerobe and an obligate phototroph. It can use hydrogen sulphide, thio- 

 sulphate, tetrathionite, elementary sulphur, or molecular hydrogen as the 

 electron donor for carbon dioxide assimilation [29]. The quantum require- 

 ment of the light dependent process is 8 10 quanta for four hydrogen 

 atoms (or four electrons) moved with molecular hydrogen, thiosulphate or 

 tetrathionite as the reducing agent [30]. This agreement with the value 

 obtained with the other photosynthetic organisms implies a fundamental 

 similarity in the basic light-dependent events (cf. [34]). In the laboratory 

 the organism is cultured in an inorganic medium containing carbonate, 

 sulphide and thiosulphate [31]. Depending upon growth conditions and 

 age, the in vivo absorption spectrum shows differences due to variation in 

 the content of accessory pigment (Fig. i). All the data reported here are 

 based upon cultures with a moderate amount of accessory pigment. It has 

 recently been demonstrated [37] that contrary to previous assumptions, at 

 least two different molecular species of chlorophyll exist among the green 

 bacteria. The organism used in this study contains Chlorohium chlorophyll- 

 650 and is strain L. 



A representation of the submicroscopic morphology of this organism 

 can be obtained by electron microscopy of ultra-thin sections. Typically, 

 the organisms are fixed by exposure to osmium tetroxide at a concentration 



