Regulation of d -Xylose Metabolism in Caulobacter crescentus by a LacI-Type Repressor

Abstract

ABSTRACT In the oligotrophic freshwater bacterium Caulobacter crescentus , d -xylose induces expression of over 50 genes, including the xyl operon, which encodes key enzymes for xylose metabolism. The promoter (P xylX ) controlling expression of the xyl operon is widely used as a tool for inducible heterologous gene expression in C. crescentus . We show here that P xylX and at least one other promoter in the xylose regulon (P xylE ) are controlled by the CC3065 ( xylR ) gene product, a LacI-type repressor. Electrophoretic gel mobility shift assays showed that operator binding by XylR is greatly reduced in the presence of d -xylose. The data support the hypothesis that there is a simple regulatory mechanism in which XylR obstructs xylose-inducible promoters in the absence of the sugar; the repressor is induced to release DNA upon binding d -xylose, thereby freeing the promoter for productive interaction with RNA polymerase. XylR also has an effect on glucose metabolism, as xylR mutants exhibit reduced expression of the Entner-Doudoroff operon and their ability to utilize glucose as a sole carbon and energy source is compromised.