Glutamate excretion in Escherichia coli: dependency on the relA and spoT genotype

Glutamate excretion due to amino acid starvation was investigated in "stringent" and "relaxed" strains of Escherichia coli. The observed excretion process is relA-dependent, carrier-mediated, and glutamate-specific. After induction, excretion was detected within less than 2 min and continued for more than 5 h with a rate of 7-10 nmol (mg dry weight)-1 min-1. Using carbonyl cyanide m-chlorophenylhydrazone or polymyxin B nonapeptide, together with valinomycin, it was shown that glutamate excretion is driven by the membrane potential.