A nutrient medium for development of cell dense inoculum in mixotrophic mode to seed mass culture units of Dunaliella salina

Dunaliella salina is cultivated extensively in natural ponds or intensively in race way ponds for β-carotene production. The ponds are seeded with culture inoculum developed in laboratory conditions or in pilot plant. Because of its high light requirement for growth, D. salina cultures are very cell dilute. Therefore, a large volume of culture inoculum is required to seed mass culture units. The feasibility of culture of D. salina in mixotrophic mode to obtain cell dense inoculum was investigated with an Indian isolate – I3. The constituents of the mineral medium and their concentration were first standardized in growth assays. The optimized mineral medium was supplemented with organic carbon sources – glycerol, sodium acetate and malt extract and organic nitrogen sources – yeast extract and peptone to test for the best results of mixotrophic culture. A mineral medium with 100 mg L–1 potassium nitrate or urea, 0.35 mg L–1 potassium phosphate, 1 ml L–1 trace elements mix (Walne's medium) without borate and 12.5 % NaCl in sea water was found optimal. Malt and yeast extracts in the proportion of 1:3 g L–1 in optimized mineral medium was found to result in cell dense cultures. Mixotrophically cultured inoculum grown photoautotrophically in optimized mineral medium resulted in increased biomass production with higher carotene content than when photoautotrophically cultured. The production cycle decreased by 11 days compared to autotrophic cultures