Chemosystematic evaluation of the genus <i>Scytonema</i> (Cyanobacteria) based on occurrence of phycobiliproteins, scytonemin, carotenoids and mycosporine-like amino acid compounds

Forty unicyanobacterial cultures of the genus Scytonema, isolated from terrestrial habitats worldwide (Europe, America, Southeast Asia, Australia and Africa), were investigated. The pigments detected were four phycobiliproteins (allophycocyanin, phycocyanin, phycoerythrocyanin and phycoerythrin), scytonemin, six carotenoids (β-carotene, canthaxanthin, echinenone, isozeaxanthin, myxoxanthophyll and zeaxanthin) and14 different mycosporines, including shinorine, stanierine and asterina-330. Cluster analyses indicated three groups among the isolates which were not related to their biogeographical origins. The first was composed of isolates with allophycocyanin and phycocyanin; β-carotene, canthaxanthin, echinenone and zeaxanthin; and scytonemin but no MAAs. These isolates had disc-shaped or elongated cells with blue-green cytoplasm and slight meristematic zones. The second group comprised isolates containing allophycocyanin, phycocyanin and phycoerythrin; β-carotene, canthaxanthin, echinenone, isozeaxanthin and myxoxanthophyll; and also both MAAs and scytonemin. Here, the cells were elongated with brown-violet cytoplasm and marked meristematic zones. The third group comprised isolates with allophycocyanin, phycocyanin and phycoerythrocyanin; β-carotene, canthaxanthin and echinenone; shinorine-type MAA, but no scytonemin. The cells were elongate with blue-green cytoplasm and marked terminal meristematic zones, and the organisms grew in dimly lit places. Multivariate statistical analyses were performed to identify compounds with especial value for taxonomy. Allophycocyanin, phycocyanin, phycoerythrin and phycoerythrocyanin; scytonemin; isozeaxanthin, myxoxanthophyll and zeaxanthin; and shinorine, asterina-330 and mycosporine 13, showed statistically significant variations among the three groups of Scytonema unicyanobacterial cultures. These results, and the fact that the biomarkers studied were conserved, even during long-term cultivation, suggest that these compounds can be used as chemotaxonomic markers in taxonomic and phylogenetic studies of Scytonema.