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.
Highlights
Bacterial pathogens often encounter limited availability of carbon, nitrogen and energy sources during their life cycles due to competition with the host organism and the commensal microbiota for nutrients
Typhimurium 14028 cultivated in minimal medium (MM) with MI is the manifestation of a heterogeneous growth phenotype that is abolished in the absence of the iol gene repressor IolR or the presence of at least 0.55% CO24
When strain 14028 was pregrown on MM/MI agar plates, adjusted to an optical density at 600 nm (OD600) = 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
Summary
Bacterial pathogens often encounter limited availability of carbon, nitrogen and energy sources during their life cycles due to competition with the host organism and the commensal microbiota for nutrients. Typhimurium 14028 cultivated in minimal medium (MM) with MI is the manifestation of a heterogeneous growth phenotype that is abolished in the absence of the iol gene repressor IolR or the presence of at least 0.55% CO24. This phenotypic heterogeneity correlates with the bistable expression of iolE and iolG, the products of which catalyze the first steps in MI degradation. Competitive growth assays suggested that induced cells suffer a growth disadvantage in the absence of MI, a constraint that might contribute to the tight repression of iol gene transcription in rich medium
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call