30 THE BACTERIAL PHOTOCHEMICAL APPARATUS 



AEROBIC OXIDATION 



ANAEROBIC OXIDATION 



H3C 



^3^. 



51 



Gl 



OH 



71 



Fig. 5. Hypothetical scheme for the introduction of the conjugated 

 keto-group in carotenoids of photosynthetic bacteria. 



The cyclization step is still a major unsolved problem. The bicyclic 

 /?- carotene constitutes a minor component of the carotenoid complex 

 of Rhodomicrohium vannielii (18,19), The monocyclic 7-carotene has 

 been claimed to be the major carotenoid produced by Chlorobiiim 

 limicola and Chlorobiuni thiosulfatophilum; a hydroxy derivative of 

 7-carotene present in the two latter bacteria was identified as rubixan- 

 thin (3- OH- r- carotene) by Goodwin and Land (17). A preliminary re- 

 investigation could not confirm their findings. The major carotenoid 

 of the two Chlorobiuni spp, exhibited an absorption spectrum in visible 

 light analogous to that of 7- carotene, but was more strongly retained 

 on aluminum oxide- containing paper than was synthetic 7- carotene. 

 The hydroxy derivative of 7-carotene from C/;ioro6?7/;» spp, can easily 

 be separated from rubixanthin; its hydroxyl group seems to be tertiary. 

 The latter pigment therefore probably represents a r,2'-dihydro-l'- 

 OH-y-carotene. We intend to investigate these findings in more detail. 

 However, the occurrence togetherof cyclic carotenoids and carotenoids 

 with aliphatic end-groups hydroxylated in 1-positions in the two CJiloro- 

 bium spp, and in Rhodomicrobium vannielii is interesting. Future 

 studies might reveal whether the latter represent intermediates or 

 alternative side-paths to the cyclic compounds. The cyclization is 

 referred to as reaction type 8 (Fig, 6), 



