Enzymatic and non-enzymatic defense mechanisms against ultraviolet-B radiation in two Anabaena species

•Defense strategies against UV-B radiation were studied in two strains of Anabaena.•SOD, CAT, APX and POD were over expressed in the UV-B irradiated cultures.•MAAs were characterized following spectroscopic, HPLC, ESI-MS, FTIR and NMR analyses.•Shinorine was the most common MAA present in both the Anabaena sp.•Porphyra-334 and mycosporine-glycine were present in Anabaena doliolum only. Enzymatic and non-enzymatic defense strategies against ultraviolet-B radiation (UV-B, 280–315nm) were studied in Anabaena doliolum and Anabaena strain L31, two of the most common strains of Indian cyanobacteria. Upon UV-B irradiation, both strains showed a 2–5-fold increase in antioxidative enzymes, such as superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and peroxidase (POD), as compared to non-irradiated control cultures. These enzymes scavenge damaging reactive oxygen species (ROS), generated by UV-B radiation inside the cells. In addition, these organisms also synthesize mycosporine-like amino acids (MAAs) which are able to carry out UV-screening and/at the same time as UV-quenching. The identification and characterization of three types of MAAs from both Anabaena species were performed using absorption spectroscopy, high performance liquid chromatography (HPLC), electro spray ionization-mass spectrometry (ESI-MS), Fourier Transform Infrared (FTIR) spectroscopy and Nuclear Magnetic Resonance (NMR) spectroscopy. Shinorine was found to be the most common MAA in both Anabaena species while porphyra-334 and mycosporine-glycine were present only in A. doliolum. The results of the present investigation clearly demonstrate that both enzymatic and non-enzymatic defense mechanisms are being employed by A. doliolum and Anabaena strain L31 to counteract the damaging effects of UV-B radiation.