CARTENOIDS OF PHOTOSYNTHETIC BACTERIA 29 



enoid synthesis in these organisms proceeds along the same lines, 

 Rps. capsulata, however, does not seem to carry the synthesis beyond 

 the stage of OH-spheroidene and OH-spheroidenone. In Fig, 4 the 

 enclosures indicate the reaction points at each step, and the reaction 

 types, given in numbers, are still restricted to the five first categories 

 presented in Table 3, 



Turning now to the Thiorhodaceae carotenoids, it is evident that 

 additional reaction types occur. Previous reports available on the 

 carotenoid composition of Chromatium spp, (12,13) can probably be 

 interpreted in favour of a distribution pattern similar to that in R. 

 rubnim and Rps. palustris, i. e., of the normal spirilloxanthin series. 

 It should be stressed at this point that the presence of lycoxanthin and 

 lycophyll has not been satisfactorily proven in any of the photosyn- 

 thetic bacteria. The pigments isolated might well have been identical 

 with rhodopin and its di- hydroxy- analogue (7), Studies with labelled 

 carbon reported by Benedict, Fuller and Bergeron (13) seem to support 

 the same reaction sequence for the carotenoid synthesis in Chromatium 

 strain D as in i?. nibrum. 



The carotenoids of four new Thiorhodaceae species have recently 

 been examined in collaboration with H. CSchlegel's group in Gottingen, 

 Chrotnatium vinosiim exhibits presumably the same carotenoid com- 

 position as does Chromatium strain D, vfhevea.s Thio spirillum jenense 

 produces lycopene and rhodopin only, according to Schmidt (14). In- 

 teresting and new features have been encountered in Chromatium 

 warmingii, which synthesizes, in addition to lycopene and rhodopin, 

 three new carotenoids, i. c, two new keto- carotenoids and one which 

 presumably is a hydroxy derivative of rhodopin with a secondary hy- 

 droxyl group (16). The huge h2.c\.ev\\xm Chromatium okenii produces a 

 major new keto- carotenoid, named okenone (15). The structure of this 

 compound is not yet established; it represents presumably a new type 

 of keto- carotenoid with a tertiary methoxyl group (15). 



The introduction of the conjugated keto group in the keto- carotenoids 

 of Rps. spp. is strictly oxygen dependent (25,26,29,31). This raises 

 the question as to the mode of biosynthesis of keto- carotenoids in 

 obligately anaerobic bacteria, like Chromatium warmingii and Chro- 

 matium okenii (32), The distribution pattern and the present, although 

 incomplete, knowledge of the structures of the carotenoids in Chroma- 

 tium warmingii might give a clue to this question. To the left in Fig, 5 

 is depicted the molecular environment at the reaction point on intro- 

 duction of the keto-group of spheroidenone (XVI), OH-spheroidenone 

 (I), or 2-keto- spirilloxanthin (XVIII) (referred to as aerobic oxidation). 

 To the right is given the predicted route for the formation of the keto- 

 carotenoid under anaerobic conditions in Chromatium warmingii by a 

 hydroxy lation (type 6), followed by a subsequent oxidation of the ally lie, 

 secondary alcohol group (type 7), 



