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In Escherichia coli K-12, components of the phosphoenolpyruvate-dependent phosphotransferase systems (PTSs) represent a signal transduction system involved in the global control of carbon catabolism through inducer exclusion, mediated by EIIACrr (=EIIAGlc), and catabolite repression, mediated by the cAMP∙CRP global regulator. We measured, in a systematic way, the relation between cellular growth rates and the key parameters of catabolite repression, i.e. the EIIACrr~P level and the cAMP levels, using in vitro and in vivo assays. Different growth rates were obtained by using either various carbon sources, or by growing the cells with limited concentrations of glucose, sucrose, and mannitol, in continuous bioreactor experiments. The ratio of EIIACrr to EIIACrr~P and the intracellular cAMP concentrations, deduced from the activity of a cAMP.CRP-dependent promoter, correlated well with specific growth rates between 0.3 h-1 and 0.7 h-1, corresponding to generation times of about 138 and 60 min, respectively. Below and above this range, these parameters were increasingly uncoupled from the growth rate, which perhaps indicates an increasing role executed by other global control systems, in particular the stringent-relaxed response system.
Copyright © 2013 by the American Society for Microbiology. [accessed 2013 July 16th]
