Tailored illumination augmenting growth and phycocyanin production by Spirulina platensis: A mixture design approach

To enhance biomass and pigments production by Spirulina platensis, a cyanobacterium known for its high phycocyanin formation, monochromatic (100), balanced (50-50) and disproportionate (70-30) dichromatic lightings of red (R), white (W) and blue (B) were examined in a 1-L glass photobioreactor. Preliminary experiments showed the positive effect of monochromatic light intensity (50, 100 and 200 mu mol/m2.s) on growth, with the highest biomass (3.95 g/L) belonging to red at intensity of 200 mu mol/m2.s. A simplex mixture design was subsequently applied to investigate biomass, phycocyanin, chlorophyll a and carotenoids concentrations as well as nutrients removal under the designed lightings at total intensity of 200 mu mol/m2.s over 30 days. The highest concentration of biomass (8.8 g/L), phycocyanin (1.41 mg/mL), chlorophyll a (0.118 mg/mL), and carotenoids (0.0345 mg/mL) corresponded to dichromatic red and blue lighting (70R-30B), showing that a small proportion of blue light alongside red is crucial for enhancing both growth and pigments production. Although the lowest concentrations belonged to monochromatic blue, phycocyanin content and nutrients (nitrate and phosphate) uptake yields on biomass were the highest for this strategy, showing the adverse effect of decreasing blue in dichromatic red and blue lighting on the overall pigments content of cell. This phenomenon can be attributed to the high photon energy of blue light, which induces cellular stress and subsequently triggers an upregulation of phycocyanin biosynthesis as a protective response. Since cultivation at industrial-scale requires the highest pigments productivity rather than cell contents of pigments, 70R-30B proved itself as the most economical strategy.