Red Light Enhances Biomass and Bioactive Compounds Through Photosynthetic Acclimation in Anabaena variabilis

Area of Science:

• * Photosynthesis and photobiology
• * Cyanobacterial physiology and biotechnology

Background:

• * Light irradiance and spectral quality critically impact cyanobacterial growth, photosynthesis, and metabolism.
• * Understanding these responses is vital for optimizing cyanobacterial cultivation and bioactive compound production.

Purpose of the Study:

• * To investigate the effects of increasing white and PAR-red light irradiances on *Anabaena variabilis*.
• * To evaluate photosynthetic efficiency, biomass productivity, and antioxidant system modulation under varying light conditions.

Main Methods:

• * Repeated-batch cultures of *Anabaena variabilis* were subjected to increasing white and PAR-red light irradiances.
• * Control cultures were maintained under constant irradiance.
• * Measurements included chlorophyll fluorescence (F_V/F_M and JIP parameters), biomass productivity, and pigment content.

Main Results:

• * *A. variabilis* maintained optimal photosynthetic efficiency (F_V/F_M) across tested light conditions.
• * PAR-red light significantly enhanced biomass productivity and induced stronger photoacclimation than white light.
• * Increased irradiance led to modulation of energy fluxes, with PAR-red light promoting thermal energy dissipation and a 30% increase in phycocyanin content.

Conclusions:

• * *Anabaena variabilis* exhibits robust acclimation to varying light irradiance and quality through coordinated photoacclimation and antioxidant responses.
• * PAR-red light is particularly effective in enhancing biomass and phycocyanin production.
• * Findings underscore the physiological flexibility of *A. variabilis* for biotechnological applications, especially for phycobiliprotein production.