Changes in cyanobacterial growth and photosynthetic pigment under different conditions

Today, cyanobacteria, as the first photosynthetic microorganisms, play an undeniable role in ecosystems and global markets. In this research, the biomass and photosynthetic pigment production under environmental and nutritional factors in Calothrix and Microchaete were investigated. Photoperiod did not influence biomass production, while both strains produced maximum biomass at a light intensity of 100 µmol photons m^-2 s^-1. Although 100 mM NaCl and 25 mM NaNO₃ increased the biomass in both cyanobacteria, urea at 1 mM inhibited the growth of Calothrix, in contrast to Microchaete. On the other hand, exposure to 10 mM hydrogen peroxide (H₂O₂) reduced Microchaete growth but did not affect Calothrix biomass. Both strains exhibited a significant increase in chlorophyll and carotenoid content under 16 h (in Microchaete) and 8 h (in Calothrix) of light exposure. Elevated NaCl concentrations (100 mM) and lower urea levels (1 mM) stimulated chlorophyll and carotenoid synthesis, while a decrease was observed under H₂O₂ treatment. The highest concentrations of total phycobiliproteins were observed at 10 and 50 µmol photons m^-2 s^-1 for Calothrix and Microchaete, respectively. While photoperiod changes did not affect total phycobiliprotein production in Microchaete, the optimal photoperiod for Calothrix was 8 h. Optimal phycobiliprotein production in Calothrix was achieved with 50 mM NaCl, 5 mM NaNO₃, and 1 mM urea, whereas Microchaete responded best to 50 mM NaCl. At 10 mM H₂O₂, the total phycobiliprotein level in Microchaete remained unchanged, while Calothrix showed decreased total phycobiliproteins. Overall, Calothrix demonstrated superior production of phycobiliproteins, including phycoerythrin and phycocyanin, compared to Microchaete, highlighting its potential for pigment-based biotechnological applications.IMPORTANCEThis research provides critical insights into the metabolic flexibility of two cyanobacteria by investigating the effect of key environmental factors-light, salinity, nitrogen source, and induced oxidative stress-on the composition of photosynthetic pigment and biomass. The observed dynamic changes in photosynthetic metabolites, especially phycobiliproteins, reveal the interesting regulatory mechanisms these strains employ for photoacclimation and stress tolerance. Understanding these metabolite relationships is important for biotechnological applications. It allows for the optimized production of valuable natural pigments and the enhancement of biomass for biofertilizers. Furthermore, the study establishes a basic model for manipulating culture conditions to direct metabolic flux toward desired compounds, offering a strategic framework for further research on microalgae and other valuable microorganisms.