Transcriptional Expression ofEscherichia coliGlutamate-Dependent Acid Resistance GenesgadAandgadBCin anhns rpoSMutant

Abstract
Resistance to being killed by acidic environments with pH values lower than 3 is an important feature of both pathogenic and nonpathogenicEscherichia coli. The most potentE. coliacid resistance system utilizes two isoforms of glutamate decarboxylase encoded bygadAandgadBand a putative glutamate:γ-aminobutyric acid antiporter encoded bygadC. Thegadsystem is controlled by two repressors (H-NS and CRP), one activator (GadX), one repressor-activator (GadW), and two sigma factors (σSand σ70). In contrast to results of previous reports, we demonstrate thatgadtranscription can be detected in anhns rpoSmutant strain ofE. coliK-12, indicating thatgadpromoters can be initiated by σ70in the absence of H-NS.