Characterization of mycosporine-like amino acids in the cyanobacterium Nostoc verrucosum.

The aquatic cyanobacterium Nostoc verrucosum forms macroscopic colonies in streams, and its appearance is superficially similar to that of the terrestrial cyanobacterium Nostoc commune. N. verrucosum is sensitive to desiccation, unlike N. commune, although these Nostoc cyanobacterial species share physiological features, including massive extracellular polysaccharide production and trehalose accumulation capability. In this study, water-soluble sunscreen pigments of mycosporine-like amino acids (MAAs) were characterized in N. verrucosum, and the mysABCD genes responsible for MAA biosynthesis in N. verrucosum and N. commune were compared. N. verrucosum produced porphyra-334 and shinorine, with porphyra-334 accounting for >90% of the total MAAs. Interestingly, porphyra-334 is an atypical cyanobacteial MAA, whereas shinorine is known as a common and dominant MAA in cyanobacteria. Porphyra-334 from N. verrucosum showed little or no radical scavenging activity in vitro, although the glycosylated derivatives of porphyra-334 from N. commune are potent radical scavengers. The presence of the mysABCD gene cluster in N. commune strain KU002 (genotype A) supported its porphyra-334 producing capability via the Nostoc-type mechanism, although the genotype A of N. commune mainly produces the arabinose-bound porphyra-334. The mysABC gene cluster was conserved in N. verrucosum, but the mysD gene was not included in the cluster. These results suggest that the mysABCD gene products are involved in the biosynthesis of porphyra-334 commonly in these Nostoc species, and that the genotype A of N. commune additionally acquired the glycosylation of porphyra-334.