Virulence Meets Metabolism: Cra and KdpE Gene Regulation in Enterohemorrhagic Escherichia coli

Abstract

Gastrointestinal (GI) bacteria sense diverse environmental signals as cues for differential gene regulation and niche adaptation. Pathogens such as enterohemorrhagic Escherichia coli (EHEC), which causes bloody diarrhea, use these signals for the temporal and energy-efficient regulation of their virulence factors. One of the main virulence strategies employed by EHEC is the formation of attaching and effacing (AE) lesions on enterocytes. Most of the genes necessary for the formation of these lesions are grouped within a pathogenicity island, the locus of enterocyte effacement (LEE), whose expression requires the LEE-encoded regulator Ler. Here we show that growth of EHEC in glycolytic environments inhibits the expression of ler and consequently all other LEE genes. Conversely, growth within a gluconeogenic environment activates expression of these genes. This sugar-dependent regulation is achieved through two transcription factors: KdpE and Cra. Both Cra and KdpE directly bind to the ler promoter, and Cra’s affinity to this promoter is catabolite dependent. Moreover, we show that the Cra and KdpE proteins interact in vitro and that KdpE’s ability to bind DNA is enhanced by the presence of Cra. Cra is important for AE lesion formation, and KdpE contributes to this Cra-dependent regulation. The deletion of cra and kdpE resulted in the ablation of AE lesions. One of the many challenges that bacteria face within the GI tract is to successfully compete for carbon sources. Linking carbon metabolism to the precise coordination of virulence expression is a key step in the adaptation of pathogens to the GI environment.

Enterohemorrhagic Escherichia coli Virulence Gene Regulation

“…A glycolytic environment, at 0.4% glucose, inhibits ler and LEE expression, whereas 0.1% glucose mimicking gluconeogenesis conditions enhances their expression (31). The LEE pathogenicity island (PAI) encodes T3SS and is organized into five major polycistronic operons and a number of bicistronic and monocistronic genes (32,33).…”

“…This regulation occurs through the proteins KdpE, a response regulator that also senses osmotic stress, and Cra, both of which bind to ler regulatory DNA. Deletion of kdpE and cra results in ablation of attaching and effacing (A/E) lesion formation by EHEC in vitro (31).…”

“…In the large intestines of humans, conditions mimicking gluconeogenic versus glycolytic metabolism are predicted to stimulate expression of the EHEC T3SS (31,139) (Fig. 4).…”

The Interplay between the Microbiota and Enterohemorrhagic Escherichia coli

“…Cra was found to directly interact with the RR KdpE, previously found to positively regulate LEE1 (52). Interestingly, KdpEdependent LEE regulation was also found to be in effect only in low-glucose conditions, and KdpE binding in vitro to the LEE1 promoter was diminished by phosphorylation (56). Presumably, under high-glucose conditions, KdpE is phosphorylated by its cognate sensor kinase, KdpD, which is activated by the glucose-sensitive IIA Ntr phosphotransfer system (57).…”

“…As a result, the colonic home of EHEC is a gluconeogenic environment. Njoroge and colleagues uncovered the importance of glucose availability in regulating T3SS by EHEC (56). Stemming from the observation that high-glucose growth media suppressed type III secretion (T3S) while low-glucose conditions induced LEE expression, the authors uncovered a role for the catabolite repressor/activator protein (Cra) in ler regulation.…”