title: SoxS-dependent coregulation of ompN and ydbK in a multidrug-resistant Escherichia coli strain.
abstract: SoxS, MarA, and Rob are homologous transcriptional activators of numerous superoxide- and antibiotic resistance genes but many of the regulated genes are yet to be characterized. In this study, microarrays and RT-PCR analysis were used to show the overexpression of the ompN porin and its upstream gene, ydbK, in an Escherichia coli multidrug-resistant mutant and in a strain constitutive for SoxS. However, transcriptional fusions revealed that SoxS (not MarA or Rob) only activated the ydbK promoter but not the ompN upstream region. RT-PCR experiments showed the overexpression of a combined ydbK - ompN transcript in the SoxS-overexpressing strain. Surprisingly, a bioinformatic approach revealed no soxbox upstream of the ydbK promoter. Thus, the ydbK and ompN genes are coexpressed in an operon and are likely activated by SoxS indirectly. It is known that YdbK is involved in superoxide resistance. Thus, individual ompN and ydbK mutants were tested for superoxide susceptibility. Nonetheless, only the ydbK mutant was susceptible to paraquat, a superoxide generator. These mutants, as well as an OmpN-overproducing strain, were further tested for antibiotic resistance. No significant decreased susceptibility was observed. Thus, ydbK plays a role in superoxide resistance but no role for either gene is found in resistance to the antibiotics tested.
authors.affiliation: Barcelona Centre for International Health Research, CRESIB, Hospital Clínic-Universitat de Barcelona, Barcelona, Spain.
authors.forename: Anna
authors.initials: A
authors.lastname: Fàbrega
authors.forename: Judah L
authors.initials: JL
authors.lastname: Rosner
authors.forename: Robert G
authors.initials: RG
authors.lastname: Martin
authors.forename: Mar
authors.initials: M
authors.lastname: Solé
authors.forename: Jordi
authors.initials: J
authors.lastname: Vila
mesh_terms: D024901:Drug Resistance, Multiple, Bacterial; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D010088:Oxidoreductases / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism; D018272:Porins / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism; D011401:Promoter Regions, Genetic; D015534:Trans-Activators / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism
chemical_list: D029968:Escherichia coli Proteins; D018272:Porins; D015534:Trans-Activators; C113199:ompN protein, E coli; C070725:SoxS protein, E coli; D010088:Oxidoreductases