GlcNAc-6P Levels Modulate the Expression of Curli Fibers byEscherichia coli

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Abstract
Curli are extracellular surface fibers that are produced by many members of theEnterobacteriaceaeand contribute to biofilm formation. The environmental cues that promote biofilm formation are poorly understood. We found that deletion of theN-acetylglucosamine-6-phosphate (GlcNAc-6P) deacetylase gene,nagA, resulted in decreased transcription from the curli-specific promoterscsgBAandcsgDEFGand a corresponding decrease in curli production inEscherichia coli. nagAis in an operon that containsnagB,nagC,nagD, andnagE, whose products are required for utilization of GlcNAc as a carbon source. NagC is a repressor of thenagBACDandnagEgenes in the absence of intracellular GlcNAc-6P. We found thatnagCmutants were also defective in curli production. Growth of a wild-type strain on media containing additional GlcNAc reduced curli gene transcription to a level similar to the level observed whennagAwas deleted. The defect in curli production innagAornagCmutants was alleviated by deletion of the GlcNAc transporter gene,nagE. Curli-producing ΔnagAsuppressor mutants whose cells were unable to take up GlcNAc were isolated. These results suggest that elevated levels of intracellular GlcNAc-6P signal cells to down-regulate curli gene expression.

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