Dynamic control of arabinose and xylose utilization inE. coli

Tailoring Escherichia coli BL21 (DE3) for preferential xylose utilization via metabolic and regulatory engineering

Xylose is the most abundant pentose in nature. However, it is usually obtained in mixtures with glucose, leading to carbon catabolite repression in many microorganisms. Among E. coli lineages, significant metabolic and regulatory differences exist, requiring distinct metabolic engineering strategies to develop a xylose-selective phenotype in the strains W, K-12, and C. In this study, strain ES02 was engineered from Escherichia coli BL21 (DE3) as a xylose-selective strain by deleting the glk, ptsG, and manZ genes. However, when grown in a mixture of xylose and glucose, this strain's specific growth rate and xylose consumption rate decreased by about 50% compared to cultures with only xylose. A modified version of the xylose-responsive transcriptional activator XylRQ31K was utilized to overcome this issue. The resulting strain ES04 (BL21 (DE3) Δglk, ΔmanZ, ΔptsG, xylR::Kmr, lacZ::xylRC91A-Gmr) efficiently used xylose as carbon source either alone or in a mixture with glucose, with a specific xylose consumption rate 75% higher than that of the wild-type strain BL21(DE3). Unexpectedly, strain ES04 partially recovers the ability to grow and consume glucose at a low rate, preferentially consuming xylose over glucose in sugar mixtures, revealing an altered carbon catabolite repression phenotype. Transcriptomics analysis suggested that glucose assimilation in this strain was related to the overexpression of the galactitol operon gatDCBAZY. Further inactivation of this operon confirmed its participation in glucose assimilation. KEY POINTS: • XylRQ31K alleviates carbon catabolite repression in the xylose-selective strain ES04. • Galactitol operon overexpression in ES04 links to partial glucose utilization. • ES04 strain preferentially uses xylose over glucose, revealing altered CCR.

L-Rhamnose Globally Changes the Transcriptome of Planktonic and Biofilm Escherichia coli Cells and Modulates Biofilm Growth

L-rhamnose, a naturally abundant sugar, plays diverse biological roles in bacteria, influencing biofilm formation and pathogenesis. This study investigates the global impact of L-rhamnose on the transcriptome and biofilm formation of PHL628 E. coli under various experimental conditions. We compared growth in planktonic and biofilm states in rich (LB) and minimal (M9) media at 28 °C and 37 °C, with varying concentrations of L-rhamnose or D-glucose as a control. Our results reveal that L-rhamnose significantly affects growth kinetics and biofilm formation, particularly reducing biofilm growth in rich media at 37 °C. Transcriptomic analysis through RNA-seq showed that L-rhamnose modulates gene expression differently depending on the temperature and media conditions, promoting a planktonic state by upregulating genes involved in rhamnose transport and metabolism and downregulating genes related to adhesion and biofilm formation. These findings highlight the nuanced role of L-rhamnose in bacterial adaptation and survival, providing insight into potential applications in controlling biofilm-associated infections and industrial biofilm management.

Availability of the Molecular Switch XylR Controls Phenotypic Heterogeneity and Lag Duration during Escherichia coli Adaptation from Glucose to Xylose

The glucose-xylose metabolic transition is of growing interest as a model to explore cellular adaption since these molecules are the main substrates resulting from the deconstruction of lignocellulosic biomass. Here, we investigated the role of the XylR transcription factor in the length of the lag phases when the bacterium Escherichia coli needs to adapt from glucose- to xylose-based growth. First, a variety of lag times were observed when different strains of E. coli were switched from glucose to xylose. These lag times were shown to be controlled by XylR availability in the cells with no further effect on the growth rate on xylose. XylR titration provoked long lag times demonstrated to result from phenotypic heterogeneity during the switch from glucose to xylose, with a subpopulation unable to resume exponential growth, whereas the other subpopulation grew exponentially on xylose. A stochastic model was then constructed based on the assumption that XylR availability influences the probability of individual cells to switch to xylose growth. The model was used to understand how XylR behaves as a molecular switch determining the bistability set-up. This work shows that the length of lag phases in E. coli is controllable and reinforces the role of stochastic mechanism in cellular adaptation, paving the way for new strategies for the better use of sustainable carbon sources in bioeconomy.