Catabolite repression in Escherichia coli is a phenomenon in which the presence of certain carbon sources hinders the utilization of other carbon sources. It is understood that cyclic nucleotide cAMP is an allosteric effector of the global transcriptional regulatory protein CRP, which in turn regulates transport and utilization of many carbon sources. Since the glucose-specific active transport system (glucose PTS) exerts negative control on the cAMP-catalyzing enzyme adenylate cyclase (AC) and thus cAMP level, this phenomenon was aptly termed the “glucose effect”. More recently, new insights such as inducer exclusion, cAMP-independent repression, and autoregulation have increased the knowledge base on the underlying mechanisms behind catabolite repression.

A derepressed phenotype (simultaneous instead of sequential sugar consumption) would be a desired characteristic of industrial biocatalysts. We are pursuing a comprehensive strategy to engineer derepressed phenotypes in E. coli based on established knowledge of regulatory cascades, as applied to the glucose-xylose model: (1) replacement of CRP-dependent promoters of the divergent xylose operons (xylAB and xylFGHR) with constitutive synthetic promoters, (2) engineering of cAMP-insensitive CRP (CRP*) in place of wild-type CRP, (3) engineering of glucose PTS-insensitive AC (cyaA*) in place of wild-type AC, and (4) systematic inactivation of the glucose PTS components (ptsG, ptsHIcrr). Inactivation of the glucose PTS (ΔptsG) results in derepressed phenotype, at the expense of growth rate (0.11 vs. 0.29 hr^-1 in wild-type). Complementation of this strain with alternative, passive glucose transport (galactose permease galP and glucokinase glk) restores growth and glucose uptake rates. Transcriptional profiling of ΔptsG vs. wild-type strains confirms the upregulation of xylose-related genes, and as indicated by the downregulation of flagellar genes, suggests a novel link between catabolite repression and biofilm formation.