Molecular Identification of Some Selected Cyanobacteria and Their Antioxidant Activities

Cyanobacteria, photosynthetic prokaryotes, are promising sources of biologically active compounds with antioxidant properties, attracting interest in their potential applications in the food, pharmaceutical, and cosmetic sectors. This present study aimed to use 16S rRNA sequences for identification of some selected strains of cyanobacteria which were previously morphologically identified. The investigation of their antioxidant activities was also performed by ABTS radical scavenging assay, ORAC-fluorescein assay and metal chelating assay in this study. Molecular identification of 8 isolates revealed 1 Calothrix sp., 2 Nostoc sp., 2 Amazonocrinis sp., 2 Aulosila sp., and 1 from the Hapalosiphonaceae family. Aulosila sp. exhibited the highest ABTS inhibition (IC50: 18.87 µg/µL), followed by a Hapalosiphonaceae cyanobacterium (19.11 µg/µL) and Calothrix sp. (21.74 µg/µL). The ORAC-fluorescein assay showed Nostoc sp. TUBT05 and a Hapalosiphonaceae cyanobacterium had the highest peroxyl radical scavenging with TE values of 0.22 and 0.21 µg/µL, respectively. Nostoc sp. TUBT01 demonstrated the highest metal chelating activity (IC50: 36.48 µg/µL). The combined analysis of selected cyanobacteria revealed insights into the relationship between their taxonomy and antioxidant profiles, highlighting their potential as natural antioxidant sources. HIGHLIGHTS 16S rRNA sequencing, BLAST, and phylogenetic analysis successfully reclassified previously morphologically identified cyanobacterial isolates. Eight cyanobacterial strains were found to have antioxidant activity, indicating their potential as a source of antioxidants. Antioxidant profiling of the selected cyanobacteria classified them into 3 major groups, revealing interesting correlations between taxonomic classification and antioxidant potential. GRAPHICAL ABSTRACT