Study of amino acids as nitrogen source in Chlamydomonas reinhardtii

All five L‐amino acids tested (L‐serine, L‐lysine, L‐leucine, L‐cysteine and L‐arginine) were used by Chlamydomonas reinhardtii as sole nitrogen source. Among these, L‐Cys was special as it has not been reported before. While these amino acids could be used in the dark only in the presence of acetic acid, in conditions of light they could support the growth of C. reinhardtii without the supplementation of acetic acid. When cultured in the TAP‐N medium, the chlorophyll content was found to be lower in the dark, but higher in the light for the cells grown with L‐Arg than with other four amino acids. Exogenously supplied L‐Ser and L‐Lys did not accumulate in the cells, demonstrating that they were used by supplying ammonium to the cells from the activity of an extracellular deaminase. Further results showed that the induction of the extracellular deaminase activity required a period of nitrogen starvation, regardless of the medium containing acetic acid or not. Results also showed that the uptake of L‐Cys was similar to L‐Leu, most likely via passive diffusion. When L‐Cys and L‐Leu were supplied together to the nitrogen‐starved cells, the absorption of L‐Cys did not affect the uptake of L‐Leu.