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 glucos e fluctuations that may occur in large-scale fed-batch cultivations. T he concentration of ppGpp was measured in laboratory-scale glucose lim ited fed-batch cultivations. Starvation zones were imitated by using a n 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 consumptio n of the residual glucose in dependence on the test system, which is m uch 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 contro l cultivations. Possible physiological consequences by an enhanced str ingent response in cultivations with limited mass transfer have to be considered.