Uropathogenic Escherichia coli strains generally lack functional Trg and Tap chemoreceptors found in the majority of E. coli strains strictly residing in the gut

Abstract

The prevalence and function of four chemoreceptors, Tsr, Tar, Trg, and Tap, were determined for a collection of uropathogenic, fecal-commensal, and diarrheagenic Escherichia coli strains. tar and tsr were present or functional in nearly all isolates. However, trg and tap were significantly less prevalent or functional among the uropathogenic E. coli strains (both in 6% of strains) than among fecal-commensal strains (both in > or =50% of strains) or diarrheal strains (both in > or =75% of strains) (P < 0.02).

FIG. 1.

Presence of trg and tap gene sequences among uropathogenic and fecal-commensal strains as determined by Southern blot analysis. BglI-digested genomic DNA from each of nine UPEC and three fecal-commensal (FC) strains was electrophoresed on an 0.8% agarose gel and subjected to Southern blot analysis with digoxigenin-labeled 5′ and 3′ fragments of the trg (A) and tap (B) genes. Lane designations are the same for both blots. Lanes: 1, CFT073; 2, CFT108; 3, CFT204; 4, CFT269; 5, CFT325; 6, F3; 7, F11; 8, F24; 9, F54; 10, EFC4; 11, EFC9; 12, K-12.

FIG. 2.

Chemotaxis of uropathogenic, fecal-commensal, and diarrheagenic E. coli strains to human urine, amino acids, saccharides, and dipeptide. Numerous pyelonephritis (blue), cystitis (red), fecal-commensal (green), and diarrheagenic (magenta) E. coli strains were assayed for their ability to respond chemotactically to human urine (A), l-serine (B), l-aspartate (C), d-ribose (D), d-galactose (E), and l-Gly-Leu (F). Strains were cultured from motility agar and grown to mid-exponential phase (optical density at 600 nm of 0.3 to 0.4) in tryptone broth, pelleted, and resuspended in chemotaxis buffer to starve at 30°C for 1 h. Starved bacterial suspensions (500 μl of ∼10¹⁰ total CFU) were added to wells of chemotaxis chambers along with microcapillaries filled with attractant (undiluted or diluted in chemotaxis buffer) or chemotaxis buffer alone as a negative control. Chemotaxis chambers were incubated at 30°C for 90 min before the capillaries were removed and the contents were diluted and plated. Data are represented in a box-and-whiskers format, with the box extending from the 25th percentile to the 75th percentile, with a line at the median or 50th percentile. Whiskers extend from the box to include the highest and lowest data points. Filled boxes indicate capillaries filled with attractant, while open boxes indicate capillaries filled with chemotaxis buffer only. All strain names are indicated along the y axis. , P < 0.05.

FIG. 3.

Deletion and nonsense mutations of trg and clonal deletion of tap from the tar-tap-cheRBYZ operon of different UPEC strains compared to full-length trg and tap in K-12. (A) The trg gene region from K-12 was aligned with homologous regions from UPEC strains CFT073, F11, and UTI89 by using ClustalW software (MegAlign, Lasergene 7). Bold lines indicate regions of homology of the trg genes of CFT073, F11, and UTI89 to the K-12 trg gene and surrounding DNA sequence. Gaps within the lines indicate that regions of trg and flanking sequence have been deleted from the UPEC strains. Both UPEC strains CFT073 and UTI89 appear to have acquired the same (or clonal) deletion (from the exact position upstream to position 1196 of trg). F11 has acquired a couple of smaller deletions, including that at position 186 of trg which results in a frame shift and premature stop in Trg translation. (B) An alignment of the 5′ region of both trg sequences from K-12 and F11 is shown along with the deletion at position 186 in F11 and the predicted effect on translation of both Trg sequences. An asterisk indicates the stop codon. (C) The tar-tap-cheRBYZ operon from K-12 was aligned with the same operon from UPEC strains CFT073, F11, and UTI89 using ClustalV software (MegAlign, Lasergene 7). Bold lines indicate regions of homology of CFT073, F11, and UTI89 to the K-12 tar-tap-cheRBYZ operon. Gaps within the lines indicate regions of the tap gene that have been deleted from the UPEC strains. All UPEC strains appear to have acquired the same (or clonal) deletion (from positions 109 to 1484 of tap). (D) An alignment of the 5′ and 3′ regions of tap from K-12, CFT073, F11, and UTI89 is shown and highlights the clonality of the tap deletion in the UPEC strains.