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

Abstract

Growth of Salmonella enterica serovar Typhimurium strain 14028 with myo-inositol (MI) is characterized by a bistable phenotype that manifests with an extraordinarily long (34 h) and variable lag phase. When cells were pre-grown in minimal medium with MI, however, the lag phase shortened drastically to eight hours, and to six hours in the absence of the regulator IolR. To unravel the molecular mechanism behind this phenomenon, we investigated this repressor in more detail. Flow cytometry analysis of the iolR promoter at a single cell level demonstrated bistability of its transcriptional activation. Electrophoretic mobility shift assays were used to narrow the potential binding region of IolR and identified at least two binding sites in most iol gene promoters. Surface plasmon resonance spectroscopy quantified IolR binding and indicated its putative oligomerization and high binding affinity towards specific iol gene promoters. In competitive assays, the iolR deletion mutant, in which iol gene repression is abolished, showed a severe growth disadvantage of ~15% relative to the parental strain in rich medium. We hypothesize that the strong repression of iol gene transcription is required to maintain a balance between metabolic flexibility and fitness costs, which follow the inopportune induction of an unusual metabolic pathway.

Identification of the conservediolgene cluster involved in rhizosphere competence inPseudomonas

“…Our analyses of publicly available genome-wide fitness data show that root colonization in vitro depends primarily on the iolR, iatABC, and dksA genes, while being seemingly independent of inositol consumption. Additionally, IolR does not affect inositol consumption, contrasting with previous results (Dong et al, 2020;Hellinckx et al, 2017;Kohler et al, 2011), but is required for root colonization and exhibits many links to metabolism of diverse carbon sources. Moreover, swimming motility appears to be inhibited by DksA, suggesting that the induction of swimming by inositol in our experiments might be due to an inositolinduced repression of DksA.…”

“…The IolCEBIDG enzymes potentially catalyze five consecutive reactions that transform the sugar alcohol myo-inositol successively into scyllo-inosose (IolG), trihydroxycyclohexadione (IolE), deoxyglucuronate (IolD), deoxy-keto-glucuronate (IolB), deoxy-keto-gluconate-6-phosphate (DKGP; IolC), and malonate semialdehyde and dihydroxyacetone phosphate (DHAP; IolC) (Figure 2d), which could theoretically enter other pathways or be directed towards anabolism as acetyl-CoA in a reaction catalyzed by MmsA/IolA, which is codified elsewhere in both pseudomonad genomes. The predicted transcriptional repressor of the locus, IolR, is inhibited by the interaction with the intermediate product DKGP, allowing the expression of the entire locus (Dong et al, 2020;Hellinckx et al, 2017;Kohler et al, 2011).…”

Metabolism in the Niche: a Large-Scale Genome-Based Survey Reveals Inositol Utilization To Be Widespread among Soil, Commensal, and Pathogenic Bacteria

“…The genome of Oceanobacillus oncorhynchi carries a 76-kb fragment with 34 genes predicted to be involved in inositol degradation. Many functions, including those of the two regulators ReiD and IolR, which play a pivotal role in the regulation of MI degradation ( 19 , 22 , 23 ), are encoded twice, and 12 putative dehydrogenases providing the substrate for IolE were identified ( Fig. 2b ).…”

IolR, a negative regulator of the myo-inositol metabolic pathway, inhibits cell autoaggregation and biofilm formation by downregulating RpmA in Aeromonas hydrophila

“…One of the most fundamental aspects of infectious diseases is microbial access to host nutrients. Bacterial pathogens often encounter a limited availability of carbon, nitrogen, and energy sources during infections while competing with other microorganisms for nutrients 3 . Increasing evidence suggests that pathogens have developed specific metabolic strategies to overcome these restrictions to increase their fitness in the nutrient-poor environments 4 .…”