Untapped Potential of Terrestrial Unicellular Cyanobacteria as Potential Bioresource for Polyphenolics and...

Unicellular cyanobacteria due to their faster growth and ease of cultivation can be used as potential cell factories for different biotechnologically important metabolites. In the present study, methanolic extracts of twenty different terrestrial unicellular cyanobacteria were evaluated for antioxidant properties. DPPH activity ranged between 9.28 and 37.77% while ABTS activity was in a range of 48.22-100.00%. Fe^+ 2 chelating activity ranged from 39.62 to 98.66% and deoxyribose protection (DRP) activities ranged between 41.18 and 71.53%. Total phenolic content (TPC) and total flavonoid content (TFC) were found to be in the range of 17.87-81.67 µg GAEs g^- 1 FW and 0.30-7.46 mg QEs g^- 1 FW respectively. Aphanothece sp. K93 and Chroococcidiopsis sp. K63 had significant ABTS and DPPH radical scavenging activity. The ferrous ion chelating activity for these two isolates was recorded as 98.66 ± 0.53% and 90.846 ± 0.27% respectively, while the DRP was noted as 64.36 ± 0.23% and 62.482 ± 0.25% respectively. Aphanothece sp. K93 was recorded with the highest TPC (81.67 ± 0.84 µg GAE g^- 1 FW) whereas Cyanobacterium aponinum K17 showed the highest TFC (7.46 ± 0.12 mg QE g^- 1 FW). TPC was significantly positively correlated with DPPH, and ferrous ion chelating activity while TFC showed negative correlation with ABTS activity. Untargeted metabolite profiling of Aphanothece sp. K93 via LC-MS analysis, showed the abundance of bis(4-ethylbenzylidene)sorbitol; cetrimonium; ethyl-N-[(3alpha,7alpha,12alpha)-3,7,12-trihydroxy-24-oxocholan-24-yl]glycinate and myristoyl glutamic acid with known bioactive properties. Rare bioactive compounds like artemotil and militarinone A were also putatively annotated from the MS analyses. Due to the presence of high phenolics, radical scavenging activity and bioactive metabolites in unicellular cyanobacteria (like Aphanothece sp. K93), it can be further explored as potential cell factory for bioactive phenolic compounds for applications in pharmaceutical industries.