Cross-regulation among arabinose, xylose and rhamnose utilization systems in E-coli

Bacteria frequently encounter multiple sugars in their natural surroundings. While the dynamics of utilization of glucose-containing sugar mixtures have been well investigated, there are few reports addressing regulation of utilization of glucose-free mixtures particularly pentoses. These sugars comprise a considerable fraction in hemicellulose which can be converted by suitable biocatalysts to biofuels and other value-added products. Hence, understanding of transcriptional cross-regulation among different pentose sugar utilization systems is essential for successful development of industrial strains. In this work, we study mixed-sugar utilization with respect to three secondary carbon sources - arabinose, xylose and rhamnose at single-cell resolution in Escherichia coli. Our results reveal that hierarchical utilization among these systems is not strict but rather can be eliminated or reversed by altering the relative ratios of the preferred and nonpreferred sugars. Since transcriptional cross-regulation among pentose sugar systems operates through competitive binding of noncognate sugar-regulator complex, altering sugar concentrations is thought to eliminate nonspecific binding by affecting concentration of the regulator - sugar complexes