Regulation and stimulation of photosynthesis of mixotrophically cultured Haematococcus pluvialis by ribose

Abstract The low cell growth rate of Haematococcus pluvialis is a major barrier to achieve low-cost production of the biomass. Our previous study demonstrated that ribose could significantly enhance the growth rate and cell activity of H. pluvialis under mixotrophic conditions. This study showed the photosynthetic rate of the algal cells cultured with ribose was two-fold higher than that of phototrophic after 2-day cultivation. The increased photosynthetic activity of the cells with mixotrophic culture using ribose occurred earlier than that with sodium acetate. Similar photosynthetic fluorescence characteristics was observed for cells grown in phototrophic and ribose-fed culture. Photosystem (PS) I of ribose-fed cells was enlarged relative to PS II after two days. The difference in rubisco activity and subunit gene (rbcL and rbcS) expression however, was not significant between phototrophic and mixotrophic cultivation. The photosynthetic rate of H. pluvialis doubled with ribose mainly due to the high reaction of the Calvin cycle. The results suggested that metabolites derived from ribose could provide additional substrates for the Calvin cycle. This study provides the evidence about unique ribose utilization patterns by H. pluvialis during photosynthesis processes in mixotrophic culture mode. By understanding the mechanism of ribose metabolism in H. pluvialis under mixotrophic cultivation, it offers a promising route for improvement of biomass accumulation.