This study examined the genes under the control of FlhDC and sigmaF in E. coli. Under defined steady-state growth condition, we used two different genetic approaches to alter the modulator concentration in cells; (1) moderately expressing FlhDC or sigmaF from anhydrotetracycline (aTc) inducible and Tet repressor-controlled PLtet promoter in a plasmid-borne flhDC or fliA gene; (2) disrupting the expression of FlhDC or sigmaF in flhDC or fliA deletion mutant strains. Samples were taken from culture with wild-type or deletion strains at mid log phase (OD=0.2) or from overexpression strains at mid log phase (OD=0.2) before or 5 minutes after moderate induction. Samples were then RNA-stabilized using Qiagen RNAProtect Bacterial Reagent (Qiagen). Total RNA was then isolated using MasterPure kits (Epicentre Technologies). Purified RNA was reverse-transcribed to cDNA, labeled and hybridized to Affymetrix GeneChip E. coli Antisense Genome Arrays as recommended in the technical manual (www.affymetrix.com). Meanwhile, we characterized, when growth conditions decline, CRP activation allows E. coli to devote progressively more of its limited reserves to actively search for better conditions. This sample is taken from wild-type strain at mid-log phase to serve as control.
