Evaluation of potent cyanobacteria species for UV-protecting compound synthesis using bicarbonate-based culture system

The present investigation evaluates the potential of three cyanobacteria species Anabaena cylindrica, Nostoc commune and Synechococcus BDUSM-13 for photo-protecting mycosporine-like amino acids (MAAs) synthesis using bicarbonate-based culture system. Current investigations witnessed noteworthy bicarbonate tolerance of all species (NaHCO₃; 0.5, 1 and 2 g L^{- 1}) in terms of their growth rate, chlorophyll content, biomass productivity and carbon fixation ability. Among all strains, Synechococcus BDUSM-13 showed maximum surge in specific growth rate (i.e. 0.72 day^-1) at 1 g L^-1, productivity (i.e. 0.92 ± 0.06 g day^-1 L^-1) and chlorophyll content (i.e. 0.09 g L^-1) at 2 g day^-1 L^-1. Synechococcus cells were also has the 0.48 g dw^-1 carbon content with highest CO₂ fixation rate (i.e. 0.653 g.CO₂ mL^-1 day^-1) at 2 g L^-1. Though, they were not able to produce MAAs after long UV-B exposure (i.e. 24 and 48 h). A. cylindrica strain was the most competent species for the bicarbonate-based approach, produced UV-protecting iminomycosporine compound (i.e. shinorine, λ _max at 334 ± 2 nm) along with carbon fixation (i.e. 0.49 g CO₂ mL^-1 day^-1) at 2 g L^-1 NaHCO₃. This suggests the bicarbonate supplementation during cultivation is a promising strategy to increase cellular abundance, biomass productivity and carbon fixation in cyanobacteria. However, UV-B irradiation may cause species-specific differences in the MAAs synthesis to produce UV-protecting compounds.