SlyA Protein Activates fimB Gene Expression and Type 1 Fimbriation in Escherichia coli K-12

Abstract

We have demonstrated that SlyA activates fimB expression and hence type 1 fimbriation, a virulence factor in Escherichia coli. SlyA is shown to bind to two operator sites (OSA1 and OSA2), situated between 194 and 167 base pairs upstream of the fimB transcriptional start site. fimB expression is derepressed in an hns mutant and diminished by a slyA mutation in the presence of H-NS only. H-NS binds to multiple sites in the promoter region, including two sites (H-NS2 and H-NS3) that overlap OSA1 and OSA2, respectively. Mutations that disrupt either OSA1 or OSA2 eliminate or reduce the activating effect of SlyA but have different effects on the level of expression. We interpret these results as reflecting the relative competition between SlyA and H-NS binding. Moreover we show that SlyA is capable of displacing H-NS from its binding sites in vitro. We suggest SlyA binding prevents H-NS binding to H-NS2 and H-NS3 and the subsequent oligomerization of H-NS necessary for full inhibition of fimB expression. In addition, we show that SlyA activates fimB expression independently of two other known regulators of fimB expression, NanR and NagC. It is demonstrated that the rarely used UUG initiation codon limits slyA expression and that low SlyA levels limit fimB expression. Furthermore, Western blot analysis shows that cells grown in rich-defined medium contain ∼1000 SlyA dimers per cell whereas those grown in minimal medium contain >20% more SlyA. This study extends our understanding of the role that SlyA plays in the host-bacterial relationship.

Whole Genome Sequence Analysis of the First Australian OXA-48-Producing Outbreak-Associated Klebsiella pneumoniae Isolates: The Resistome and In Vivo Evolution

“…In addition, there is also a SNP present in slyA , which encodes a known transcriptional regulator of virulence genes. SlyA is involved in conferring resistance to antimicrobial peptides and oxidative stress in salmonellae [31], [32] as well as regulation of fimbriae in E. coli , which have an important role in colonization and pathogenesis [33]; based on the crystal structure of SlyA, the resulting amino acid change (V120G) is located between two α-helices involved in dimerization [34]. Although the functional consequences of these mutations are not directly known, it is interesting that they occurred during 18 months of intra-abdominal carriage after an initial outbreak event that resulted in patient deaths.…”

Molecular Characterization of the Vacuolating Autotransporter Toxin in Uropathogenic Escherichia coli

“…H-NS regulates the transcription of several UPEC genes by competing for binding to their promoter element with a MarR-type regulatory protein; this includes SfaX binding to the sfa 2 fimbrial promoter (80), PapX binding to the flhDC flagellum master regulator promoter (92), and SlyA binding to the type 1 fimbria fimB recombinase promoter (93). The SfaX and PapX regulator genes are cotranscribed as part of their respective upstream fimbrial operon (encoding S-and P-type fimbriae, respectively [47,80]).…”

OmpR regulation of the uropathogenic Escherichia coli fimB gene in an acidic/high osmolality environment

“…Levels of fimB expression were highest in a neutral pH/low osmolality condition and lowest in a low pH/high osmolality medium. A switch from a neutral pH/low osmolality environment that favours fimB activation by SlyA (a proposed activator of fimB transcription, McVicker et al, 2011) or RcsB (another proposed activator of fimB transcription, Schwan et al, 2007) to a low pH/high osmolality environment found in the human urinary tract that favours OmpR could have relevance in regulating fimB (Schwan, 2011). OmpR could displace SlyA or RcsB on the fimB promoter site as the OmpR level increases in UPEC growing in an acidic/high osmolality environment.…”