Effects of gluconate on biomass improvement and light stress tolerance of Haematococcus pluvialis in mixotrophic culture

Abstract Mixotrophic culture shows great potential for improving microalgal growth. Currently, the complex roles of organic carbon for biomass enhancement in mixotrophic culture remain a topic of investigation. In this study, the green microalgae Haematococcus pluvialis was cultured for biomass production under mixotrophic conditions using a new organic carbon source, sodium gluconate. Experiments feeding H. pluvialis with sodium gluconate, sodium acetate, and ribose were conducted. The best growth performance was achieved with sodium gluconate exposed to high light intensity. With the addition of 2 g/L gluconate, the maximum cell number achieved 2.43 × 106/mL at 105 ± 3 μmol m−2 s−1 light intensity, a five-fold increase over that of heterotrophic culture and 89.8% increase over ribose-fed mixotrophic culture. The maximum dry cell weight was 2.09 g/L with a specific growth rate of 0.48 d−1, an increase of 77.1% over that with optimal ribose conditions. The cellular motility of microalgae was affected by the culture age and light intensity. At lower light intensity (45 ± 3 μmol m−2 s−1), the highest motile cell number was 7.33 × 105/mL with gluconate. Under mixotrophic conditions, the culture with gluconate kept high numbers of motile cells with the increase of light intensity, 3.17 × 105/mL at 105 ± 3 μmol m−2 s−1. Even high light intensity caused decrease in cellular motility, gluconate-fed microalgae still had active cell activity with more motile cells compared with that fed with ribose. Microalgae with gluconate triggered resistant response against high light intensity under mixotrophic conditions. Moreover, H. pluvialis showed great potential in effective photosynthesis with higher chlorophyll content under high light condition. These results indicate that gluconate is an effective organic carbon source for improving biomass productivity, cell activity, and photosynthesis efficiency for H. pluvialis in mixotrophic culture.