. Here, we show that whereas NanR, a sialic acid-response regulator, binds to region 1, NagC, a GlcNAc-6P-responsive protein, binds to region 2 instead. The NanR-and NagC-binding sites lie adjacent to deoxyadenosine methylase (Dam) methylation sites (5 -GATC) that are protected from modification, and the two regulators are shown to be required for methylation protection at regions 1 and 2, respectively. Mutations in nanR and nagC diminish fimB expression, and both fimB expression and FimB recombination are inhibited by GlcNAc (3-and >35-fold, respectively). Sialic acid catabolism generates GlcNAc-6-P, and whereas GlcNAc disrupts methylation protection by NagC alone, Neu5Ac inhibits the protection mediated by both NanR and NagC as expected. Type 1 fimbriae are proinflammatory, and host defenses enhance the release of both Neu5Ac and GlcNAc by a variety of mechanisms. Inhibition of type 1 fimbriation by these amino sugars may thus help balance the interaction between E. coli and its hosts. type 1 fimbriae

SummaryThe phase variation of type 1 fimbriation in Escherichia coli is controlled by the inversion of a 314 bp element of DNA, determined by FimB (switching in both directions) or FimE (switching from the ON-to-OFF orientation predominantly), and influenced by auxiliary factors IHF, Lrp and H-NS. The fimB gene is separated from the divergently transcribed yjhATS operon by a large (1.4 kbp) intergenic region of unknown function. Here, we show that fimB expression is regulated by multiple cis-active sequences that lie far upstream ( > 600 bp) of the transcription start sites for the recombinase gene. Two regions characterized further (regions 1 and 2) show sequence identity, and each coincides with a methylation-protected Dam (5 ¢ ¢ ¢ ¢ -GATC) site. Regions 1 and 2 apparently control fimB expression by an antirepression mechanism that involves additional sequences proximal to yjhA . Region 1 encompasses a 27 bp DNA sequence conserved upstream of genes known ( nanAT ) or suspected ( yjhBC ) to be involved in sialic acid metabolism, and we show that FimB expression and recombination are suppressed by Nacetylneuraminic acid. We propose that E. coli recognizes the amino sugars as a harbinger of potential host defence activation, and suppresses the expression of type 1 fimbriae in response.

The cell walls of Gram-positive bacteria consist primarily of a macromolecular matrix comprising similar amounts of peptidoglycan and covalently attached anionic polymers. Under most growth conditions the anionic polymers of Bacillus subtilis are principally teichoic acids ; in strain 168 these include a polyglycerol teichoic acid and a glucose/galactosamine-containing teichoic acid. However, when cultures are subjected to phosphate stress the bacterium induces a complex series of responses, one of which is the replacement of at least part of the wall teichoic acid with teichuronic acid, a non-phosphatecontaining anionic polymer. In this paper the construction of a transcriptional reporter strain that facilitates the monitoring of the promoter region upstream of the tua operon involved in teichuronic acid synthesis and its controlled expression are reported. The expression of the tua operon was monitored in both phosphate-starved, non-growing batch cultures and phosphate-limited continuous cultures. We show that the transcription of the operon correlates well with the anionic polymer composition of the cell walls.