The Effects of Light Sources on Nutrient Production in the Growth Phase of Chlamydomonas Reinhardtii

The development of microalgae as a source of energy, medicine, and food is widely recognized as valuable, but the process is very complex and the effects of each individual variable are not yet fully understood. Light source is one important variable that greatly affects the growth rate and nutrient composition of algae and could be a simple method to control them in scaled operations requiring unique outcomes. The purpose of this research is to compare the growth rates of Chlamydomonas reinhardtii, a model alga strain, under differing light sources: Cool White and Gro-Lux. Cool White lights have a more evenly distributed spectrum whereas Gro-Lux lights have very sharp peaks around 440 and 660 nm, which are substantially closer to the peak absorbances of chlorophylls a and b. The initial cell concentration, growth media composition, and electric power input to lights were controlled. The dry weight, as well as the concentrations of protein, carbohydrates, and chlorophylls a and b were measured during the growth phase. The dry weights did not differ significantly between the different light sources. This might give the impression that lights focused on the peak absorbances of chlorophylls a and b do not yield significantly greater growth; however, power input to the light sources does not necessarily correspond to real photon flux, which was 120 µmol m^-2 s^-1 for Cool White and 80 µmol m^-2 s^-1 for Gro-Lux. Even at roughly equal dry weights, there was significant variation in the composition of nutrients. Cool White lights yielded 288% more carbohydrates whereas Gro-Lux produced 188% more protein and about 108% more chlorophyll. These results show that nutrient composition is affected by changing light exposure wavelengths, and could lead to greater control or optimization in the future.