Bistability in myo -Inositol Utilization by Salmonella enterica Serovar Typhimurium

Abstract

The capability of Salmonella enterica serovar Typhimurium strain 14028 (S. Typhimurium 14028) to utilize myo-inositol (MI) is determined by the genomic island GEI4417/4436 carrying the iol genes that encode enzymes, transporters, and a repressor responsible for the MI catabolic pathway. In contrast to all bacteria investigated thus far, S. Typhimurium 14028 growing on MI as the sole carbon source is characterized by a remarkable long lag phase of 40 to 60 h. We report here that on solid medium with MI as the sole carbon source, this human pathogen exhibits a bistable phenotype characterized by a dissection into large colonies and a slow-growing bacterial background. This heterogeneity is reversible and therefore not caused by mutation, and it is not observed in the absence of the iol gene repressor IolR nor in the presence of at least 0.55% CO 2 . Bistability is correlated with the activity of the iolE promoter (P iolE ), but not of P iolC or P iolD , as shown by promoter-gfp fusions. On the single-cell level, fluorescence microscopy and flow cytometry analysis revealed a gradual switch of P iolE from the "off" to the "on" status during the late lag phase and the transition to the log phase. Deletion of iolR or the addition of 0.1% NaHCO 3 induced an early growth start of S. Typhimurium 14028 in minimal medium with MI. The addition of ethoxyzolamide, an inhibitor of carboanhydrases, elongated the lag phase in the presence of bicarbonate. The positive-feedback loop via repressor release and positive induction by bicarbonate-CO 2 might allow S. Typhimurium 14028 to adapt to rapidly changing environments. The phenomenon described here is a novel example of bistability in substrate degradation, and, to our knowledge, is the first demonstration of gene regulation by bicarbonate-CO 2 in Salmonella.

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

“…1A). The length of this lag phase was characterized by a low level reproducibility, which was reflective of the stochastic and heterogeneous growth behaviours under this condition as indicated by high standard deviations4. In contrast, when strain 14028 was pregrown on MM/MI agar plates, adjusted to an OD 600  = 0.8 and diluted as described, the resulting culture exhibited a much shorter lag phase of 8 h, which could be attributed to the fact that the cells had already adapted to MI utilization.…”

“…Typhimurium cells harbouring P iolE in the ON status is remarkably low in the absence of MI4. Therefore, in light of the high binding affinity of IolR, we speculated that a strong selective force acts on the cells.…”

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

“…This electrolyte is secreted at large amounts by the proximal duodenum (Sewell and Young, ; Hogan and Isenberg, ) and serves probably as an in vivo signal to appropriately activate the MI degradation cascade. When growing on MI as carbon and energy source, strain 14028 exhibits a bistable phenotype that is characterized by the dissection of a population into few distinct colonies and a slow‐growing background (Kröger et al ., ). This phenotype is reversible, and bistability is not observed with iolR ‐negative strains or in the presence of bicarbonate.…”

In Vivo Tracking of Streptococcal Infections of Subcutaneous Origin in a Murine Model

“…BLAST search of this hypothetical protein is 100 % homologous to a protein identified in the M1 strain of GAS as a sugar phosphate isomerase or epimerase ( iolE ) involved in carbohydrate transport and metabolism. Fluorescence microscopy studies of green fluorescence protein (GFP) driven under the iolE promoter in Salmonella enterica subspecies 1 serovar Typhimurium strain 14028 revealed strict repression of GFP-expression when grown on D-glucose-rich medium [30]. Therefore, we assayed the bioluminescence production of Xen20 cells, washed, and resuspended in M9 minimal medium with a range of D-glucose concentrations from 0 to 6 mM (Fig.…”