Response of a rice-field cyanobacterium Anabaena sp. HKAR-7 upon exposure to ultraviolet-B radiation and ammonium chloride

• Published in: Environmental Sustainability 2021-03, Vol.4 (1), p.95-105
• Main Authors: Singh, Deepak Kumar, Pathak, Jainendra, Pandey, Abha, Singh, Vidya, Ahmed, Haseen, Kumar, Deepak, Rajneesh, Sinha, Rajeshwar Prasad
• Format: Article
• Language: English
• Subjects: Absorption spectra; Amino acids; Ammonium; Ammonium chloride; Anabaena; Biosynthesis; Carotenoids; Chlorides; Chlorophyll; Climate Change; Cyanobacteria; Earth and Environmental Science; Electron transport; Environment; Environmental Management; Exposure; Gene amplification; High performance liquid chromatography; Ionization; Light; Liquid chromatography; Mass spectrometry; Mass spectroscopy; Maximum likelihood method; Mycosporine-like amino acids; Natural Resources; Nitrogen; Original Article; Photosynthetic pigments; Photosynthetically active radiation; Photosystem II; Phycocyanin; Phylogenetics; Pigments; Proteins; Quantum efficiency; Sustainable Development; Transport rate; Ultraviolet radiation
• ISSN: 2523-8922; 2523-8922
• DOI: 10.1007/s42398-020-00146-6

Interactive effects of ultraviolet radiation (UVR), photosynthetically active radiation (PAR) and exogenously supplied ammonium chloride (NH 4 Cl) was studied in the rice-field cyanobacterium Anabaena sp. HKAR-7. The cyanobacterium was cultured under varying NH 4 Cl concentrations i.e., 0, 50, 200, 500, 1000 and 5000 μM and 200 μM (concentration) was found to be optimum for the growth of the cyanobacterium. Detrimental effects of UV-B exposure were observed on photosynthetic pigments such as chlorophyll a (Chl a ), carotenoids and phycocyanin (PC). However, damage to these pigments was less in the cyanobacterial samples supplemented with NH 4 Cl. Contents of Chl a and PC in cyanobacterial cells decreased upon UV-B exposure but decrement was less in the samples supplemented with NH 4 Cl. Upon UV-B exposure, carotenoids content enhanced initially (till 15 days) during the course of treatment (21 days) but significant decrease (in carotenoids content) was observed in later phase of the experiment. From the results of photosynthetic activity, maximum quantum efficiency of PSII ( Fv/Fm ) and maximum electron transport rate (ETR max ), it could be concluded that exogenous supplementation of NH 4 Cl (optimum concentration) helped in protecting the cyanobacterial cells from highly energetic UVR to certain extent. Another interesting observation was significantly higher levels of biosynthesis and accumulation of mycosporine-like amino acids (MAAs) in the cyanobacterial cells supplemented with NH 4 Cl in comparison to non-supplemented cells. The purified MAA was identified to be phorphyra-334 as evidenced by UV/VIS absorption spectra, high performance liquid chromatography (HPLC) and electrospray ionization-mass spectrometry (ESI–MS).