RELIEVING EFFECTS OF GLYCINE AND METHIONINE FROM ACETIC-ACID INHIBITION IN ESCHERICHIA-COLI FERMENTATION

Among amino acids screened for their potential to relieve wild and recombinant Escherichia coli from the negative effects of acetic acid, glycine, and methionine showed a sparing effect. In the presence of 2 g/L of acetic acid, addition of 0.5 g/L of glycine or methionine resulted in either a complete recovery or a further enhancement in the specific growth rate, while the enhancement was significant but not fully complete in the presence of 4 g/L of acetic acid. The addition of 0.5 g/L of methionine alleviated the negative effect of acetic acid on recombinant E. coli growth to produce more beta-lactamase, which was encoded by plasmid pUC18. In continuous fermentation the methionine effect on recombinant E. coli metabolism depended on dilution rate; at high dilution rates, above 0.4 h-1, the methionine addition enhanced beta-lactamase production and reduced acetic acid formation, while at low dilution rates, below 0.3 h-1, the effect was reversed. In fed-batch fermentation with wild-type E. coli, cell growth rate and cell yield from glucose were enhanced with methionine addition, while the acetic acid concentration reached over 4 g/L.