Improvement of photosynthesis in dense microalgal suspension by reduction of light harvesting pigments

The effects of light-harvesting pigments (LHP) in microalgal cells on photosynthetic activity in a dense cell suspension were examined. The results suggest that a lower LHP content should result in higherphotosynthetic productivity under high light intensity. The idea was first proposed by Lien and San Pietro in 1975 that photosynthesis could be improved by reducing the LHP content in microalgal cells, but this has not been demonstrated in detail. Experiments to evaluate the idea were conducted with Synechocystis PCC 6714 and Chlorella pyrenoidosa. In the experiments with PCC 6714, photosynthesis of a phycocyanin-deficient mutant was compared with that of the wild type. In the experiments with C. pyrenoidosa, the LHP content was controlled by the light intensity in the algal culture. The maximum photosynthetic activity was 20-30% higher in the dense suspension of cells having a lower LHP content with both organisms. These results indicate that the idea of reducing the LHP content could he applicable to a wide variety of photosynthetic organisms.