The Escherichia coli genome encodes for a number of pentose transporters. Each pentose regulon encodes for at least one transporter, in a few instances two. While the expression of specific transporters is conditional on the presence of its cognate sugar (e.g. xylose transporters are expressed in the presence of xylose), significant regulatory crosstalk exists between different pentose regulons. Furthermore, the transporters are not specific and therefore capable of transporting a broad spectrum of sugars.

By profiling gene expression in different transporter knockouts and regulatory mutants, we have developed a model for pentose transport regulation in the presence of multiple sugars. Our model suggests that this regulation induces a hierarchy in pentose utilization. As transport is a rate-limiting step in pentose metabolism, our results and model may aid in the metabolic engineering of strains using pentose sugars as feedstock, such as in cellulosic biofuel production and natural product synthesis.