Response of guanosine tetraphosphate to glucose fluctuations in fed-batch cultivations of Escherichia coli.

A rapid transient increase of guanosine 3'-diphosphate 5'-diphosphate (ppGpp) in Escherichia coli was found in response to short-term glucose fluctuations that may occur in large-scale fed-batch cultivations. The concentration of ppGpp was measured in laboratory-scale glucose limited fed-batch cultivations. Starvation zones were imitated by using an intermittent feeding scheme or a two-compartment reactor system. The cellular concentration of ppGpp per biomass increased from 80 nmol to 300-600 nmol per g cell dry weight within only 1 min after consumption of the residual glucose in dependence on the test system, which is much faster than earlier described in literature. Readdition of glucose caused immediate reduction of the ppGpp to the basic level which did not differ in cultivations with simulated starvation zones from control cultivations. Possible physiological consequences by an enhanced stringent response in cultivations with limited mass transfer have to be considered.