The orphan regulator ReiD of Salmonella enterica is essential for myo‐inositol utilization

Abstract

SummaryIn Salmonella enterica serovar Typhimurium (S. Typhimurium), the genomic island GEI4417/4436 is responsible for the utilization of myo-inositol (MI) as carbon and energy source. Here, we report the characterization of a novel, island-encoded positive autoregulator termed ReiD (STM4423) that is specific to certain S. enterica strains and Escherichia coli strain ED1a able to use MI. ReiD was essential for growth with this polyol and also contributed to S. Typhimurium proliferation in swine caecum content. Providing higher copy numbers of ReiD reduced the long lag phase of 2 days during growth of S. Typhimurium in MI medium by 50%. In a heterologous host, expression of ReiD activated the transcription from the promoter of iolE/ iolG, whose products catalyse the initial two steps in MI degradation. Episomal expression of iolE/iolG1 rescued the otherwise zero growth phenotype of a reiD deletion mutant in MI medium. Gel mobility shift assays with purified ReiD demonstrated directed interaction of ReiD with its own promoter and that of iolE. The repressor IolR bound the reiD promoter, implying that reiD is part of the IolR regulon. Taken together, the regulator ReiD is a trigger to accelerate the switch from more easily accessible nutrients to MI utilization by S. Typhimurium.

High binding affinity of repressor IolR avoids costs of untimely induction of myo-inositol utilization by Salmonella Typhimurium

“…The binding of IolR to most iol promotor regions was demonstrated previously236. To delineate a molecular model for the interaction of IolR and its target sites, we here performed EMSAs using different-length promoter fragments that represented possible IolR binding regions.…”

“…Next, 5-deoxy-glucuronic acid is isomerized by IolB to 2-deoxy-5-keto-D-gluconic acid, which is in turn phosphorylated by the kinase IolC and degraded to dihydroxyacetone phosphate, acetyl coenzyme A and CO 2 . The activator ReiD has been shown to interact with the promoter of iolE and thus to positively regulate iol gene expression3.…”

Identification of a Repressor for the Two iol Operons Required for Inositol Catabolism in Geobacillus Kaustophilus

“…The process of regulation of iol genes by IolR homologs could be conserved among a number of bacterial species, including Gram-negative bacteria. For instance, Sinorhizobium meliloti belonging to Alphaproteobacteria, was shown to possess the iol genes regulated by its IolR ortholog [9], and in Salmonella enterica, belonging to Gammaproteobacteria, its IolR ortholog was found to regulate not only the transcription of iol genes [10] but also an orphan regulator encoded by reiD involved in myo-inositol utilization [11].…”

Regulation of fucose and 1,2-propanediol utilization by Salmonella enterica serovar Typhimurium

“…Proliferation of S. Typhimurium was impaired in gnotobiotic mice by a lack of sialic acids due to co-colonization with a sialidase-deficient Bacteroides thetaiotaomicron strain ( Ng et al, 2013 ). The iol genes responsible for the degradation of myo -inositol ( Kröger and Fuchs, 2009 ; Kröger et al, 2011 ; Rothhardt et al, 2014 ) are thought to contribute to the virulence of S. Typhimurium in mice, pigs, chickens, and calves ( Lawley et al, 2006 ; Carnell et al, 2007 ; Chaudhuri et al, 2009 , 2013 ). Growth attenuation has been reported in food, nematodes, and mice for S. Typhimurium deficient in ethanolamine utilization ( Stojiljkovic et al, 1995 ; Srikumar and Fuchs, 2011 ; Thiennimitr et al, 2011 ).…”