Characterization of the Escherichia coli AF/R1 pilus operon: novel genes necessary for transcriptional regulation and for pilus-mediated adherence.

We isolated the genetic determinant of AF/R1 pilus production in attaching/effacing Escherichia coli RDEC-1 and identified seven genes required for pilus expression and function. DNA sequence analysis of the structural subunit gene afrA corrected an error in the published sequence and extended homology with the F18 pilus subunit of pig edema E. coli strains. AfrB and AfrC, encoded downstream from AfrA, were required for pilus expression. AfrB was related to the usher protein PefC of Salmonella typhimurium plasmid-encoded fimbriae, and AfrC was related to PefD, a chaperone protein. AfrD and AfrE, encoded downstream from AfrC, were not necessary for the expression of AF/R1 pili but were required for ileal adherence as assayed by ileal brush border aggregation. Thus, the adhesive subunit of the AF/R1 pilus is distinct from the structural subunit, as is the case for Pap pili and type 1 pili. AfrD was related to FedE of the F18 fimbrial operon of the E. coli strain that causes edema disease in pigs. AfrE was a novel protein. AfrR and AfrS are encoded upstream from AfrA, in the opposite orientation. AfrR is related to the AraC family of transcriptional regulators, and AfrR and AfrS interact to function in a novel mode of transcriptional activation of afrA. AF/R1 pili mediate the adherence to Peyer's patch M cells, ileal mucosa, and colonic mucosa in a rabbit model of diarrhea caused by enteropathogenic E. coli. Our observations will facilitate the further study of the phenomena of M-cell adherence.

Development of experimental model of chronic pyelonephritis with Escherichia coli O75:K5:H-bearing Dr fimbriae: mutation in the dra region prevented tubulointerstitial nephritis.

Escherichia coli that express Dr fimbriae and related adhesins recognize the common receptor decay accelerating factor. E. coli strains that express adhesins of the Dr family were postulated to be associated with cystitis (30-50%), pregnancy-associated pyelonephritis (30%), and chronic diarrhea (50%). In this study, we investigated the hypothesis that E. coli renal interstitial binding mediated by the Dr adhesin may be important for the development of chronic pyelonephritis. An insertional dra mutant, E. coli DR14, of the clinical E. coli isolate IH11128 bearing Dr fimbriae, was constructed and used to characterize persistence of infection and interstitial tropism in an experimental model of ascending pyelonephritis. Quantitative cultures of kidney homogenates indicated that Dr hemagglutinin positive (Dr+) E. coli IH11128 established a 1-yr colonization of renal tissue. In the Dr hemagglutinin negative (Dr-) group, 50% of animals cleared infection within 20 wk and 100% between 32 to 52 wk. Dr+ E. coli colonized the renal interstitium. Significant histological changes corresponding to tubulointerstitial nephritis including interstitial inflammation, fibrosis, and tubular atrophy were found in the kidney tissue of the Dr+ but not the Dr- group. A substantial amount of fimbrial antigen was detected in the parenchymal regions affected by interstitial inflammation and fibrosis. The obtained results are consistent with the hypothesis that mutation within the dra region, affecting E. coli binding to tubular basement membranes, prevented renal interstitial tropism and the development of the changes characteristically seen in tubulointerstitial nephritis.

Canopy photosynthesis and its relationship to plant productivity in near-isogenic cotton lines differing in leaf morphology.

A 2-year study was conducted to determine the relationships between plant canopy photosynthesis, canopy light interception, and plant productivity of cotton (Gossypium hirsutum L.) exhibiting differing leaf morphologies. The near-isogenic lines were from a single background (MD 65-11) and represented the leaf shapes Normal (small leaf lobing), Sub-Okra (intermediate leaf lobing), Okra (large leaf lobing), and Super Okra (severe leaf lobing). The F(1) of a cross Normal x Okra (intermediate leaf lobing) and the F(2) (segregating 1:2:1 for Normal Sub-Okra, and Okra, respectively) were also grown. Reduced plant canopies were produced by Okra and Super Okra lines, which translated into increased light penetration to the ground, and hence, in reduced canopy photosynthesis. Integrated canopy photosynthesis (ICAP) was significantly associated with light interception by the plant canopy. Part of the remaining variability in ICAP was associated with confounding factors associated with plant maturity and other unmeasured genotypic factors. Intermediate (F(1) and Sub-Okra) and normal leaf types displayed the largest ICAP values in both years. Lint production was positively related to ICAP (R(2) = 0.53). The combination of high ICAP values and competitive lint yields indicate that intermediate lobed leaf morphologies offer promise as productive sources of physiological variation for cotton germplasm development.