Dissolved Amino Acids and Platymonas Nutrition

摘要

The marine flagellate Platymonas subcordiformis rapidly accumulated amino acids at concentrations likely to be found in nature. The relation between velocity of uptake and substrate concentration was determined and the apparent maximum uptake velocity estimated. Accumulated amino acids entered both synthetic and oxidative pathways. The contribution of the uptake mechanism at an ambient glycine concentration of 1.0 micromole/liter to the nitrogen requirement of the cell was about roughly 10% for optimal laboratory growth conditions in batch culture (North and Stephens, 1967). Cells were also cultured in a continuous flow apparatus at different levels of inorganic nutrient supply. This produced changes in cell nitrogen content and growth rate of the population. An eleven-fold increase in amino acid uptake rate was observed at low levels of inorganic nutrients. Thus amino acid uptake could fulfill the entire nitrogen requirement in Platymonas at free amino acid concentrations in the normal ecological range. We conclude that dissolved amino acids may be important in the nitrogen nutrition of some algae in the sea. (Author)