Molar growth yields and enterotoxin B production of Staphylococcus aureus S-6 with amino acids as energy sources

Staphylococcus aureus S-6 was able to utilize glutamate, proline, histidine, aspartate, alanine, threonine, serine, or glycine as a major energy source, when these were added singly at a concentration of 2.5 g/liter to a base medium containing salts, vitamins, and 30 mg of each of 18 amino acids per liter. Molar growth yields (Y) for each of the eight amino acids were determined in aerobic batch cultures. Except with aspartate and serine, all molar growth yields decreased with increasing concentration of the energy source, whether or not it was present in excess. The average molar growth yields for both aspartate and serine were Y = 35 g/mol. The highest Y values obtained with the other amino acids were 79, 78, 56, 46, 58, and 21 g/mol for glutamate, proline, histidine, alanine, threonine, and glycine, respectively. Histidine was not utilized as an energy source at concentrations of less than 2 mM. Enterotoxin yields (mg of toxin per g [dry wt] of cells) higher than in the basal medium were obtained when proline, histidine, alanine, serine, and glycine were the major energy sources. When proline and alanine were the major energy sources, enterotoxin yields were not affected by the concentration, whereas toxin yields were reduced at high concentrations of the other six amino acids. The highest cell yields and Y values were obtained with glutamate, but its utilization as an energy source markedly reduced enterotoxin yields.