The relationship between carotenoids and sunlight response in members of the family Micrococcaceae.

The aim of this study was to compare the photoprotective effect of carotenoids in phylogentically related bacteria, which synthesize structurally different pigments. Two organisms were isolated from the same environment. Their 16S rDNA sequences and phenotypic characteristics identified them as members of the family Micrococcaceae. Reverse phase HPLC and absorption spectroscopy revealed that one of them, designated RMB40, synthesized 3 carotenoids with 9 conjugated double bonds, whilst the other, designated RMB42, synthesized a single and more hydrophobic pigment carrying 11 conjugated double bonds. Survival curves were obtained during sunlight exposure for both organisms and for carotenoid deficient mutants derived from them. Increased sunlight sensitivity was found in the carotenoidless mutant derived from RMB42. In contrast, pigment depletion had no appreciable effect on the sunlight response of RMB40. It is concluded that the structure of bacterial carotenoid probably exert an important influence on the effectiveness of these compounds to provide photoprotection in vivo.