Résumé
The glucose-xylose metabolic transition is of growing interest as a modelto explore cellular adaption since these molecules are the main substrates resultingfrom the deconstruction of lignocellulosic biomass. Here, we investigated the role ofthe XylR transcription factor in the length of the lag phases when the bacteriumEscherichia colineeds to adapt from glucose- to xylose-based growth. First, a variety oflag times were observed when different strains ofE. coliwere switched from glucoseto xylose. These lag times were shown to be controlled by XylR availability in the cellswith no further effect on the growth rate on xylose. XylR titration provoked long lagtimes demonstrated to result from phenotypic heterogeneity during the switch fromglucose to xylose, with a subpopulation unable to resume exponential growth, whereasthe other subpopulation grew exponentially on xylose. A stochastic model was thenconstructed based on the assumption that XylR availability influences the probability ofindividual cells to switch to xylose growth. The model was used to understand howXylR behaves as a molecular switch determining the bistability set-up. This work showsthat the length of lag phases inE. coliis controllable and reinforces the role of stochas-tic mechanism in cellular adaptation, paving the way for new strategies for the betteruse of sustainable carbon sources in bioeconomy.