Abstract
Catabolite repression refers to the process where the metabolism of one sugar represses the genes involved in metabolizing another sugar. While glucose provides the canonical example, many other sugars are also known to induce catabolite repression. However, less is known about the mechanism for catabolite repression by these non-glucose sugars. In this work, we investigated the mechanism of catabolite repression in the bacterium Escherichia coli during growth on lactose, L-arabinose, and D-xylose. The metabolism of these sugars is regulated in a hierarchical manner, where lactose is the preferred sugar, followed by L-arabinose, and then D-xylose. Previously, the preferential utilization of L-arabinose over D-xylose was found to result from transcriptional crosstalk. However, others have proposed that cAMP governs the hierarchical regulation of many non-glucose sugars. We investigated whether lactose-induced repression of L-arabinose and D-xylose gene expression is due to transcriptional crosstalk or cAMP. Our results demonstrate that it is due to cAMP and not transcriptional crosstalk. In addition, we found that repression is reciprocal, where both L-arabinose and D-xylose also repress the lactose gene expression, albeit to a lesser extent and also through a mechanism involving cAMP. Collectively, the results further our understanding of metabolism during growth on multiple sugars.
Highlights
Catabolite repression refers to the process where the metabolism of one sugar represses the genes involved in metabolizing another sugar
And 5a, lactose still inhibited arabinose and xylose gene expression in strains unable to metabolize these respective sugars. These results demonstrate that lactose-mediated repression of the arabinose and xylose genes is independent of arabinose and xylose metabolism
While much is known about how E. coli regulates its metabolism when grown on a single sugar, far less is known about how this bacterium regulates its metabolism when grown on mixtures of sugars, when the mixture does not involve glucose
Summary
Catabolite repression refers to the process where the metabolism of one sugar represses the genes involved in metabolizing another sugar. We investigated the mechanism of catabolite repression in the bacterium Escherichia coli during growth on lactose, L-arabinose, and D-xylose The metabolism of these sugars is regulated in a hierarchical manner, where lactose is the preferred sugar, followed by L-arabinose, and D-xylose. When the cells are metabolizing glucose and EIIAGlc is predominantly in the unphosphorylated form, these sugars are not transported into the cell and, are unable to induce the expression of their cognate metabolic genes These two mechanisms are believed to be the main factors regulating glucose catabolite repression in E. coli. A recent study by Aidelberg and coworkers investigated the utilization of six non-glucose sugars (lactose, arabinose, xylose, D-sorbitol, L-rhamnose and D-ribose) in E. coli[14] They observed hierarchical expression of the metabolic genes for these sugars. These results suggest that multiple mechanisms are involved in the selective utilization of non-glucose sugars, where some involve transcriptional crosstalk, as is the case with arabinose and xylose, and others do not
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