Impact of nitrogen and drought on phycobiliprotein content in terrestrial cyanobacterial strains

Cyanobacteria are highly adaptable microorganisms, characterized by an ability to survive in different environments with unfavorable conditions. In order to determine the content and composition of phycobiliproteins in cyanobacterial strains, depending on environmental factors, such as drought, darkness, and lack of nutrients in the substrate, the quantity of these pigments was investigated in 21 cyanobacterial strains. The study was conducted with terrestrial, filamentous, N₂-fixing cyanobacterial strains, which belong to Nostoc and Anabaena genera, isolated from different soil types in the Vojvodina region (Serbia). All strains were cultivated in nitrogen-free medium, medium with nitrate concentration of 2 g?L^?1 in the presence of light, and in drought conditions (water activity less than 0.5 %), on inorganic substrate, in the dark. Statistically significant differences of phycocyanin and allophycocyanin contents were found in the case of strains cultivated in nitrogen-free medium compared to strains grown in the medium containing nitrogen. There were no statistically significant differences in phycoerythrin and total phycobilin contents between strains grown in media with and without nitrogen. The results suggest that nitrogen availability affects composition of phycobiliproteins in the tested strains without affecting the total phycobiliprotein content, which implies maintenance of balanced pigment abundance as cyanobacterial response to nitrogen source. Significantly lower concentrations of the studied pigments, which varied from 0.8 to 16.9 μg mg^?1 dry weight, were detected in strains exposed to dry and dark conditions. These data indicate the presence of preserved phycobiliproteins after a period of 10 years of cyanobacterial exposure to drought and darkness, which can be of great importance for the study on their stability under unfavorable environmental conditions.