The effect of sodium bicarbonate supplementation on growth and biochemical composition of marine microalgae cultures

The addition of bicarbonate (NaHCO3; 0, 1, or 2 g L-1) to microalgal cultures has been evaluated for two species (Tetraselmis suecica and Nannochloropsis salina) in respect of growth and biochemical composition. In batch cultures, addition of bicarbonate (1 g L-1) resulted in significantly (P < 0.05) higher final mean cell abundances for both species. No differences in specific growth rates (SGRs) were recorded for T. suecica between treatments; however, increasing bicarbonate addition decreased SGR values in N. salina cultures. Bicarbonate addition (1 g L-1) significantly improved nitrate utilisation from the external media and photosynthetic efficiency (F (v) /F (m) ) in both species. For both T. suecica and N. salina, bicarbonate addition significantly increased the cellular concentrations of total pigments (3,432-3,587 and 19-37 fg cell(-1), respectively) compared to cultures with no additional bicarbonate (1,727 and 11 fg cell(-1), respectively). Moreover, final concentrations of total cellular fatty acids in T. suecica and N. salina cultures supplemented with 2 g L-1 bicarbonate (7.6 +/- 1.2 and 1.8 +/- 0.1 pg cell(-1), respectively) were significantly higher than those cells supplemented with 0 or 1 g L-1 bicarbonate (3.2-3.5 and 0.9-1.0 pg cell(-1), respectively). In nitrate-deplete cultures, bicarbonate addition caused species-specific differences in the rate of cellular lipid production, rates of change in fatty acid composition and final lipid levels. In summary, the addition of sodium bicarbonate is a viable strategy to increase cellular abundance and concentrations of pigments and lipids in some microalgae as well as the rate of lipid accumulation in nitrate-deplete cultures.