cAMP-Dependent Catabolite Repression is the Dominant Control Mechanism of Metabolic Fluxes under Glucose Limitation in Escherichia coli

Institute of Molecular Systems Biology, ETH Zurich, Zurich, Switzerland

^* To whom correspondence should be addressed. Email: sauer{at}imsb.biol.ethz.ch.

	Abstract

Although a whole arsenal of mechanisms are potentially involved in metabolic regulation, it is largely uncertain when, under which conditions, and to which extent a particular mechanism actually controls network fluxes and thus cellular physiology. Based on ¹³C-flux analysis in Escherichia coli mutants, we elucidated the relevance of global transcriptional regulation by ArcA, ArcB, Cra, CreB, CreC, Crp, Cya, Fnr, Hns, Mlc, OmpR and UspA on aerobic glucose catabolism in glucose-limited chemostat cultures at a growth rate of 0.1h^-1. The by far most relevant control mechanism was cAMP-dependent catabolite repression as the inducer of the PEP-glyoxylate cycle and thus low tricarboxylic acid cycle fluxes. While all other mutants and the reference E. coli exhibited high glyoxylate shunt and PEP carboxykinase fluxes, and thus high PEP-glyoxylate cycle flux, this cycle was essentially abolished in both the Crp and Cya mutants that lack the cAMP-CRP complex. Most other mutations were phenotypically silent and only the Cra and Hns mutants exhibited slightly altered flux distributions through PEP carboxykinase and tricarboxylic acid cycle, respectively. The Cra effect on PEP carboxykinase was probably the consequence of a specific control mechanism, while the Hns effect appears to be unspecific. For central metabolism, the available data thus suggest that a single transcriptional regulation process exerts the dominant control under a given condition and this control is highly specific for a single pathway or cycle within the network.