Amino acid uptake by marine phytoplankters1,2

Axenic cultures of 25 species of unicellular marine algae were tested for their ability to utilize nine common amino acids, supplied at high concentrations in batch culture, as a nitrogen source; most species were able to use several amino acids, although growth was often slower than on nitrate nitrogen. The algae were also tested for their ability to take up 14 C‐labeled amino acids supplied at low, natural concentrations. In most cases, species that could grow on an amino acid at high concentration in culture could also take up amino acids at low concentrations. Uptake rates were higher in cells that had been deprived of nitrogen during growth. In some cases, uptake rates at low concentrations—if sustained—would be sufficient to support moderate growth rates. The ability to accumulate amino acids from dilute solution occurs in many phytoplankters, particularly in species that normally occur in inshore and littoral habitats.