Ultraviolet radiation-induced generation of reactive oxygen species, DNA damage and induction of UV-absorbing compounds in the cyanobacterium Rivularia sp. HKAR-4

• UVR induced the generation of reactive oxygen species (ROS) in Rivularia sp.
• Growth of Rivularia sp. was adversely affected by UV-B radiation.
• UVR interfered with genome integrity of Rivularia sp.
• Rivularia sp. has some photoprotective machinery to overcome the effects of UVR.
• UVR induced the synthesis of UV-absorbing compounds in Rivularia sp.

The effects of ultraviolet radiation (UVR) on certain biochemical processes were studied in the cyanobacterium Rivularia sp. HKAR-4. The generation of reactive oxygen species (ROS) was investigated under 295, 320 and 395 nm cut-off filters using the ROS sensing probe 2′,7′-dichlorodihydrofluorescein diacetate (DCFH-DA). Contrary to photosynthetically active radiation (PAR) and PAR + UV-A (PA) radiation, ROS signals were more prominent under PAR + UV-A + UV-B (PAB) radiation. The low levels of ROS were also detected in the cells growing under dark as well as normal light conditions. The integrity of genomic DNA, the amplification of 16S rDNA and random amplified polymorphic DNA (RAPD) profile were considerably affected by PAB radiation. The formation of cyclobutane thymine dimers (T<>T) was observed under PAR as well as PA and PAB radiations but the intensity was found to be the highest under UV-B radiation. The formation of T<>T under PAR as well as PA radiation has not previously been reported in cyanobacterial systems. Furthermore, the synthesis of UVR-absorbing/screening compounds such as mycosporine-like amino acids (MAAs) was investigated under PAR and PAB. Dose-dependent induction of MAAs, mycosporine-glycine (MG; λmax310 nm) as well as an unknown UV-absorbing compound (λmax 335 nm) was observed under both PAR as well as UVR. The concentration of unknown MAA (hereafter, M-335) was higher than MG. Overall, in response to harmful effects of solar UVR, cyanobacteria have developed some photoprotective machinery to overcome its impact to grow in the adverse natural environments.