Constitutive mutations of the Salmonella enterica serovar typhimurium transcriptional virulence regulator phoP

The PhoP-PhoQ two-component system is necessary for the virulence of Salmon ella spp, and is responsible for regulating several modifications of the li popolysaccharide (LPS). Mutagenesis of the transcriptional regulator phoP r esulted in the identification of a mutant able to activate transcription of regulated genes similar to 100-fold in the absence of PhoQ. Sequence analy sis shelved two single-base alterations resulting in amino acid changes at positions 93 (S93N) and 203 (Q203R), These mutations were individually crea ted, and although each resulted in a constitutive phenotype, the double mut ant displayed a synergistic effect both in the induction of PhoP-activated gene expression and in resistance to antimicrobial peptides. The constituti ve phoP gene was placed under the control of an arabinose-inducible promote r to examine the kinetics of PhoP-activated gene induction and the resultan t modifications of LPS. Gene induction and 2-hydroxymyristate modification of the lipid A were shown to occur within minutes of the addition of arabin ose and to peak at 4 h. As the first constitutive mutant of phoP identified , this allele will be invaluable to future genetic and biochemical studies of this and likely other regulatory systems.