Interactions between C and N metabolism in Dunaliella salina cells cultured at elevated CO2 and high N concentrations

The green algaDunaliella salina UTEX 200 was cultured at high (5 percnt;) [CO2] in a medium containing 10 mmol/L of either NO3− or NH4+ as the sole N source. Specific growth rate was 50 percnt; higher for NH4+-grown cells than for their counterparts cultured in the presence of NO3−. Cell size, protein content, Rubisco protein, phosphoenolpyruvate carboxylase (PEPC) activity, and light independent carbon fixation were enhanced by growth in the presence of NH4+. On the other hand, maximal photosynthetic rate and cell glycerol concentration were lower when N was supplied as NH4+. The activity of glutamine synthetase was affected very little by the N-source.D. salina UTEX 200 showed some peculiarities in its mechanism of adaptation to high [N] in comparison to other strains previously used for similar studies. This allowed dissection of the underlying mechanism of the growth response to high [N], highlighting the potential role of PEPC, the main anaplerotic enzyme, as a pivotal player in the adaptation of cells to these conditions.