Photoregulated carotenoid biosynthesis in non-photosynthetic microorganisms.

Photoregulated carotenoid biosynthesis consists of an initiating photoactivation which bestows carotenogenic competence upon photochromogenic microorganisms. Subsequent carotenoid biosynthesis is light independent but requires microbial growth. Experimental systems have been developed for several photochromogcnic microorganisms to separate the primary photoact from the following carotenogenic reactions. investigations with Flavobacterium dehydrogenans have shown that photoactivated carotenogenesis is one aspect of a photoresponse which includes RNA-controlled protein biosynthesis, qualitative changes in lipids and fatty acids and a general metabolic shift-down. It is probable that the fundamental photoresponse is a readjustment of the bacterial physiology to allow existence in light and this centres upon a need to biosynthesize carotcnoid for photoprotection against photodynamic damage of the cell.