Effect of spectral quality of light on growth and cell constituents of the wild-type (WT) and DCMU-tolerant strain of microalga Scenedesmus vacuolatus

Abstract

Wild-type (WT) and DCMU-tolerant mutant strain of microalga Scenedesmus vacuolatus were used to study the effect of different spectral quality of light on the growth and biochemical constituents. Results showed that overall growth, cell constituents and total organic carbon were higher in the mutant strain than the WT under all types of light irradiances. However, green and orange light conditions were found to be optimum for both WT and mutant strain, respectively. FTIR analysis of biomass of WT and the mutant strain showed the minor difference in the lipid/carbohydrate (0.82 ± 0.061, 0.71 ± 0.05, respectively) and lipid/protein (0.52 ± 0.026, 0.59 ± 0.040, respectively) ratios due to changes in the spectral quality of light. Flow cytometer analysis of WT and mutant cells, grown under green and orange light, respectively, exhibited maximum lipid content, but the lipid content in the mutant strain was higher than the WT. The PAM fluorimeter parameters ΔF/Fm′, Fv/Fo ABS/RC, RC/ABS and ET0/RC derived from chlorophyll fluorescence induction (OJIP) curve of WT and the mutant strain showed better photosynthetic performance (RC/ABS) in the green light-grown WT and orange light-grown mutant strain. However, a reduced level of growth, cell constituents and photosynthetic yield in the WT than the mutant strain might be attributable to the higher value of NPQ, indicating greater loss of absorbed photo-energy in the WT cells. Thus, efficient utilization of spectral quality of light irradiance by the microalga was strain-specific, depending upon the photosynthetic attributes of individual strain as evident from the comparison of photosynthetic properties of both wild-type and DCMU-tolerant mutant strain.