The Accumulation of O-Succinylhomoserine by Escherichia coli and Salmonella typhimurium

Abstract

After growth of E. coli strain 7/9, the culture fluid and organisms contained an amino-acid which was shown to be O-succinylhomoserine believed to be a methionine precursor. Its accumulation indicated that it was formed in large amounts by the growing organisms. Its formation occurred equally well in the presence or absence of added homoserine and succinate, but when the succinate was added to grwoth media, synthesis occurred preferentially from it and the utilization of endogenously-formed succinate was diminished. Without added homoserine, the extent of accumulation was such (up to 440 mg O-succinylhomoserine/l) that homoserine synthesis may have increased above normal to provide the required quantities (up to 240 mg/l) of homoserine. Methionine completely suppressed accumulation of O- succinylhomoserine, threonine and lysine had no effect. A cystathionine-requiring mutant of S. typhimurium also accumulated O-succinylhomoserine; the amount (20[long dash]30 mg/l) being only about 5% of that by E. coli, and methionine prevented its accumulation by this organism. The methionine synthesis pathway in S. typhimurium which is very similar to that in E. coli is subject to end-product control.