Bioprospecting of cyanobacteria from Thai karstic caves as potential producers of phenolic compounds with antioxidant capacity

Abstract

Cyanobacteria are highly adaptable microorganisms that can survive in extreme environments. Survival of cyanobacteria in assorted habitats has positively impelled them to produce a range of bioactive compounds, which show a variety of beneficial biological activities. The karstic caves are harsh environments with low light and nutrient input and serve as a unique habitat for exploring cyanobacterial biodiversity as producers of natural products of economic and ecological importance. A total of 86 cyanobacterial strains isolated from 23 karstic caves in four regions of Thailand showed photosynthetic pigments correlated with growth performance and exhibited potential for producing phenolic compounds with significant antioxidant capacity. Based on DPPH scavenging efficiency per unit concentration of crude extract, Leptolyngbya sp. LKK14, Nostoc sp. SW02, and Leptolyngbya sp. LP01 exhibited the superior antioxidant potency. The highest contents of total phenolics (42.10 mgGAE/gCE) and flavonoids (395.90 mgQE/gCE) were found in Leptolyngbya sp. LP01 extract. The presence of phenolic compounds correlated with antioxidant activity; Leptolyngbya sp. LP01 showed the highest antioxidant activity, as measured by DPPH, ABTS, and FRAP assays, with respective values of 15.79, 20.87, and 42.69 mgAAE/gCE. Nine phenolic compounds were tentatively identified based on MS/MS fragmentation patterns compared with library data by LC-ESI-QTOF-MS/MS approach, suggesting that the extract of Leptolyngbya sp. LP01 contains valuable biological antioxidants. This study contributes to our current understanding of cyanobacterial biodiversity in poorly studied habitats, particularly in terms of their biotechnological potential as producers of secondary metabolites suitable for application in the food, pharmaceutical, and cosmetic industries.