Enhancing Chlamydomonas reinhardtii growth and metabolite biosynthesis using organic dyes as spectral converters

Abstract

The availability of light and its efficient utilisation is a major limiting factor in large scale algal cultures. While algae predominantly use the blue and red spectral regions, a significant amount of incoming light energy remains untapped outside these ranges. Converting this unused light into usable wavelengths could enhance photosynthesis. This study aimed to identify the optimal spectral converter among Lumogen Red (LR), Rhodamine 8G (R8G), and Lumogen Yellow (LY), providing efficient light utilisation for algal cultivation. Chlamydomonas reinhardtii was cultivated in double-jacketed cylindrical photo-bioreactors (PBRs) using 30% UV-a and 5% UV-b fluorescent tubes. The R8G dye displayed a slight wavelength shift with a sharp peak at about 498 nm. The LY dye demonstrated several sharp peaks at the green and blue light spectra evident of photo-degradation. The LR dye maintained better photo-stability compared to R8G and LY. Carbohydrate, lipid and protein were produced early, whereas biomass increased after day 4, as a result of photo-acclimation. The LR dye converted and emitted 3.17 × 10-19 J photon-1, enhancing biomass production and increasing photochemical energy utilisation [Y(II)] while decreasing regulated energy dissipation [Y(NPQ)]. Pigment biosynthesis was initially increased and then reduced to counteract heightened irradiation as a means of photo-protection. LR had a 1.6- and 2.9-fold up-regulation of the RuBisCo gene expression. The dye-based system correlated with improved growth, lipid, protein, carbohydrate, and pigment production. The dye-based wavelength conversion system was interlinked to the sustainable development goals addressing environmental, economic, and social aspects.