Effect of ammonium concentration on the cultivation of recombinant Escherichia coli producing penicillin G acylase

The effect of ammonium on the cultivation of r E. coli UP1, a penicillin G acylase (PGA) hyper-producer, was investigated. While r E. coli UP1 was gro wn under three different concentrations of ammonium, i.e., 0.5%, 3% and 5% ammonium sulfate, respectively, it was found that the higher the ammonium s ulfate concentration, the longer the lag phase. Cell growth and PGA activit y expression were not inhibited in the 0.5-3% ammonium sulfate cases, where as significant regulation of cell growth was found in the 5% ammonium sulfa te case. The time profile of organic acids was affected by the ammonium sul fate concentration in the medium. In the 3% ammonium case, a higher amount of lactic acid was observed. In contrast, traces of pyruvic acid were detec ted during fermentation except for the case with 5% ammonium sulfate, where pyruvic acid accumulated significantly from 10 h of fermentation.