Date Published: June 27, 2013
Publisher: Public Library of Science
Author(s): Wentong Cai, Yvonne Wannemuehler, Giuseppe Dell’Anna, Bryon Nicholson, Nicolle L. Barbieri, Subhashinie Kariyawasam, Yaping Feng, Catherine M. Logue, Lisa K. Nolan, Ganwu Li, Matthew A. Mulvey.
Two-component signaling systems (TCSs) are major mechanisms by which bacteria adapt to environmental conditions. It follows then that TCSs would play important roles in the adaptation of pathogenic bacteria to host environments. However, no pathogen-associated TCS has been identified in uropathogenic Escherichia coli (UPEC). Here, we identified a novel TCS, which we termed KguS/KguR (KguS: α-ketoglutarate utilization sensor; KguR: α-ketoglutarate utilization regulator) in UPEC CFT073, a strain isolated from human pyelonephritis. kguS/kguR was strongly associated with UPEC but was found only rarely among other E. coli including commensal and intestinal pathogenic strains. An in vivo competition assay in a mouse UTI model showed that deletion of kguS/kguR in UPEC CFT073 resulted in a significant reduction in its colonization of the bladders and kidneys of mice, suggesting that KguS/KguR contributed to UPEC fitness in vivo. Comparative proteomics identified the target gene products of KguS/KguR, and sequence analysis showed that TCS KguS/KguR and its targeted-genes, c5032 to c5039, are encoded on a genomic island, which is not present in intestinal pathogenic E. coli. Expression of the target genes was induced by α-ketoglutarate (α-KG). These genes were further shown to be involved in utilization of α-KG as a sole carbon source under anaerobic conditions. KguS/KguR contributed to the regulation of the target genes with the direct regulation by KguR verified using an electrophoretic mobility shift assay. In addition, oxygen deficiency positively modulated expression of kguS/kguR and its target genes. Taken altogether, this study describes the first UPEC-associated TCS that functions in controlling the utilization of α-ketoglutarate in vivo thereby facilitating UPEC adaptation to life inside the urinary tract.
Urinary tract infection (UTI) is one of the most common bacterial infections in humans and is a significant clinical issue worldwide. Annually, UTIs are associated with 7 million office visits, 1 million emergency room visits, 100,000 hospitalizations, and $1.6 billion in healthcare costs . In fact, ∼80–90% of community-acquired UTIs are caused by uropathogenic Escherichia coli (UPEC) . Many virulence factors are required for UPEC to cause UTIs. Typically, UTIs begin with urethral contamination with UPEC from the bowel . Successful attachment to the uroepithelium requires specific adhesins including P, type 1 and other fimbriae (such as F1C, S, M, and Dr fimbriae) , . UPEC may then ascend the urethra to enter the bladder and kidneys, where several highly regulated virulence factors, including fimbriae, secreted toxins (hemolysin, Vat, Sat, and CNF) and polysaccharide capsule, may contribute to colonization and pathogenesis . It is likely that UPEC’s ability to colonize the urinary tract and cause disease is affected by its adaptive responses to local environmental cues, including changes in nutrient availability.
One of the greatest challenges confronted by all microorganisms is adapting to rapid changes of nutrient availability in different habitats. In the course of evolution, bacteria have developed several mechanisms to sense and utilize available nutrient sources associated with particular niches or to favor the most efficiently metabolizable nutrient sources when exposed to a range of choices. TCSs are major mechanisms enabling bacteria to couple environmental stimuli to adaptive responses . The TCSs in E. coli K12 have been extensively studied –. Many TCSs that are common to both commensal and pathogenic E. coli, such as PhoQ/PhoP , QseC/QseB , , BarA/UvrY , and the AirS system  have been shown to contribute to virulence by mediating bacterial adaption to the host environment. However, no pathogen-associated TCS has yet been characterized in E. coli. Driven by the hypothesis that UPEC-associated TCSs exist to sense and respond to host environment signals distinct from those of intestinal E. coli, we identified a novel TCS C5041/C5040 significantly associated with UPEC strains, but not with EHEC, EPEC or ETEC strains. This TCS activated the expression of a genomic island involved in transport and metabolism of α-KG under anaerobic conditions. In view of these findings, C5041 was renamed KguS (α-ketoglutarate utilization sensor) and C5040 renamed KguR (α-ketoglutarate utilization regulator). These results indicated that UPEC might actively import α-KG and that α-KG could be an important carbon source for UPEC in vivo. Consistent with this observation, deletion of the TCS or its target island genes resulted in a significant reduction in a UPEC’s colonization of the murine urinary tract. To our knowledge, this is the first report of a pathogen-associated TCS in E. coli that contributes to UPEC pathogenesis.