Anaerobic photosynthetic bacteria carotenoid

Table 2. Types of reactions seen in the carotenoid biosynthesis within anaerobic photosynthetic bacteria, and cloned genes from photosynthetic bacteria and other bacteria ...

More than ten genera including about 30 species of aerobic photosynthetic bacteria have now been found (Table 9). They are distinguished from typical anaerobic photosynthetic bacteria in that they synthesize BChl only under the aerobic conditions and can not grow without even in the light. In some species, photosynthetic activities have been demonstrated. The low content of BChl, unique composition of carotenoids, and presence of non-... 

The final class of photosynthetic bacteria, the green sulfur bacteria, are named because of differences in the chemical structure of their bacte-riochlorophyll and carotenoids, giving rise to a different set of absorption bands in whole cells from their purple counterparts. This has little to do with their actual color but refers to the direction of shift of absorption wavelengths in the infrared. As photoautotrophic, strict anaerobes using sulfide or thiosulfate as an electron source, they resemble the purple sulfur bacteria and have similar electron transport chains. The sulfur that is formed as an intermediate between sulfide and sulfate is deposited out-... 

A small amount of lycopene is found in Rpi. globiformis (Table 3 S. Takaichi, unpublished) and in the diphenylamine-inhibited cultures of Chr. okenii (Schmidt et al, 1963). However in diphenylamine-inhibited cultures of Rpi. globiformis, lycopene was not reported (Schmidt and Liaaen-Jensen, 1973). Although small amounts of the intermediates of phytoene desaturase are usually found in photosynthetic bacteria, if the activity of the C-1,2 hydratase is high, lycopene as the substrate may not be found. Therefore, the carotenogenesis pathways of okenone and / .g.-keto carotenoids could possibly start from lycopene rather than from neurosporene (Fig. 7). Nothing is known about how the keto group is introduced under the anaerobic conditions. 

Erythrobacter species synthesize photosynthetic pigments including bacteriochlorophyll a and several carotenoids under highly aerobic conditions, but they can not grow anaerobically even in the light in contrast to typical photosynthetic bacteria [1]. 

A Cl transfer in the synthesis of a carotenoid has been demonstrated for the synthesis of spirilloxanthin by the photosynthetic bacterium Rhodo-spirillum rvbrum. Of labeled formate added to anaerobic, washed suspensions of the bacterium, 25 % appeared in the two methoxyl groups (Braith-waite and Goodwin, 1958) 76% was unaccounted for. Spirilloxanthin is the major photosynthetic pigment in R. rvbrum. Methoxy carotenoids have not been found outside the photosynthetic bacteria. 

---