Distribution of colored carotenoids between light-harvesting complexes in the process of recovering carotenoid biosynthesis in Ectothiorhodospira haloalkaliphila cells

• We studied the recovery of Car biosynthesis in Car-less Ect. haloalkaliphila cells.
• We examined the Car composition of LH complexes during the recovery process.
• We found the selective Car accumulation in the LH1-RC and LH2 complexes.
• We hypothesize that the LH2 assembly sites are heterogeneous in the Car composition.

The processes of recovering colored-carotenoid (Car) biosynthesis in Car-less cells of the purple sulfur bacterium Ectothiorhodospira haloalkaliphila grown with diphenylamine (DPA-cells) have been studied. It has been found that (1) the rate of recovering colored-Car biosynthesis in the lag-phase is far ahead of the growth rate of the cells themselves; (2) several Cars (ζ-carotene, neurosporene etc.) act as intermediates in Car biosynthesis; (3) because filling the “empty” Car pockets in the LH1-RC complexes is faster than in LH2, available spirilloxanthin is preferentially incorporated into the nascent LH1-RC core particles; (4) as a consequence of the resulting lack of spirilloxanthin availability, the biosynthetic intermediates (anhydrorhodovibrin, rhodopin and lycopene) fill the empty nascent LH2 Car pockets. In the present report, we further discuss the process of colored Car incorporation into LH complexes during the recovery of Car biosynthesis in the DPA-cells of Ect.haloalkaliphila.