Bioavailability of dissolved free amino acids to alga Selenastrum capricornutum

In order to understand the incubation process of algae on the low concentrations of dissolved free amino acids (DFAA), the growth of Selenastrum capricornutum was studied in the laboratory. Six individual amino acids, i.e. serine, aspartic acid, glutamic acid, glycine, alanine and arginine, were used as the sole and mixed nitrogen sources for algal incubation under axenic conditions. The results showed that algae were able to utilize various amino acids for growth; meanwhile, algae could spread different amino acids in the incubation. DFAA concentration decreased with up to 90% in the 2 days, while the cells number of algae reached to the maximum in the 6-8 days, meaning that the growth of algae cell number lags behind the decrease of the of DFAA content. In the individual amino acids experiments, rank order of the use of amino acid was: arginine>alanine>glutamic acid>aspartic acid>serine>glycine. In the mixed amino acids experiments, the cell proliferation rate of algae was significantly higher than that of individual amino acid group; meanwhile with the increase of mixed amino acid concentration, the maximum number of algal cells was also increased. Selenastrum capricornutum can also release other kinds of amino acids in the use of the individual amino acid, among them, the main release amino acids are aspartic acid and glycine. Algae could use amino acid rapidly in the lack of inorganic nitrogen condition, which provided a theoretical basis to illustrate dissolved organic nitrogen promotes algae growth.