احسان نظیفی

The terrestrial cyanobacterium Nostoc commune is a well-known species of the genus Nostoc and a cosmopolitan species that is distributed from the tropics to the polar regions of the Earth. The studies of functional molecules in N. commune, molecular taxonomical studies have revealed that N. commune can be classified into four genotypes based on differences in the 16S rRNA gene sequences. The sequence differences are not great enough to be recognized as distinct species. However, they are significantly different and allow the description of genotype A to D. These genotypes are difficult to distinguish morphologically and there are no ecophysiological differences allowing us to separate them. In this study, during the characterization of mycosporine-like amino acids (MAAs) in field isolated colonies of N. commune, three types of N. commune colonies whose water extracts resulted in different UV-absorbing spectra were found. According to an analysis of the 16S rRNA gene sequence, the N. commune colonies with absorption maxima at approximately 335, 312 and 325 nm in their water extracts were identified as genotypes A, B and D, respectively. Characterization of their MAA contents indicated that these genotypes of N. commune colonies produce structurally distinct MAAs; the genotype A produces the 478-Da, 464-Da, 508-Da and 346-Da MAAs; the genotype B produces the 1050-Da, 880-Da and 273-Da MAAs; the genotype D produces the 612-Da, 508-Da and 450-Da MAAs. These results show that three genotypes of N. commune exclusively produced their own characteristic MAAs, which supports that MAA composition could be a chemotaxonomic marker for the classification of N. commune.