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The osmotic stress response and virulence in pyelonephritis isolates of Escherichia coli: contributions of RpoS, ProP, ProU and other systems

Department of Microbiology, University of Guelph, Guelph, Ontario, N1G 2W1, Canada¹
Department of Molecular Genetics, National Institute of Genetics, Mishima, Shizuoka-ken 411, Japan²
Department of Gastrointestinal Infections, Statens Serum Institut, DK2300 Copenhagen, Denmark³

Author for correspondence: Janet M. Wood. Tel: +1 519 824 4120 Ext. 3866. Fax: +1 519 837 1802. e-mail: jwood{at}uoguelph.ca

Trehalose synthesis (RpoS-dependent) and betaine uptake mediated by transporters ProP and ProU contribute to the osmotolerance of Escherichia coli K-12. Pyelonephritis isolates CFT073 and HU734 were similar and diminished in osmotolerance, respectively, compared to E. coli K-12. The roles of RpoS, ProP and ProU in osmoregulation and urovirulence were assessed for these isolates. Strain HU734 expressed an RpoS variant which had low activity and a C-terminal extension. This bacterium accumulated very little trehalose and had poor stationary-phase thermotolerance. For E. coli CFT073, introduction of an rpoS deletion impaired trehalose accumulation, osmotolerance and stationary-phase thermotolerance. The rpoS defects accounted for the difference in osmotolerance between these strains in minimal medium of very high osmolality (1·4 mol kg^-1) but not in medium of lower osmolality (0·4 mol kg^-1). The slow growth of both pyelonephritis isolates in high-osmolality medium was stimulated by glycine betaine (GB) and deletion of proP and/or proU impaired GB uptake. An HU734 derivative lacking both proP and proU retained osmoprotective GB uptake activity that could be attributed to system BetU, which is not present in strain K-12 or CFT073. BetU transported GB (K_m, 22 µM) and proline betaine. High-osmolality human urine (0·92 mol kg^-1) included membrane-permeant osmolyte urea (0·44 M) plus other constituents which contributed an osmolality of only approximately 0·4 mol kg^-1. Strains HU734 and CFT073 showed correspondingly low GB uptake activities after cultivation in this urine. Deletion of proP and proU slowed the growth of E. coli HU734 in this high-osmolality human urine (which contains betaines) but had little impact on its colonization of the murine urinary tract after transurethral inoculation. By contrast, deletion of rpoS, proP and proU had no effect on the very rapid growth of CFT073 in high-osmolality urine or on its experimental colonization of the murine urinary tract. RpoS-dependent gene expression is not essential for growth in human urine or colonization of the murine urinary tract. Additional osmoregulatory systems, some not present in E. coli K-12 (e.g. BetU), may facilitate growth of pyelonephritis isolates in human urine and colonization of mammalian urinary tracts. The contributions of systems ProP and ProU to urinary tract colonization cannot be definitively assessed until all such systems are identified.

Keywords: osmoregulation, glycine betaine, trehalose, UPEC

Abbreviations: GB, glycine betaine; UPEC, uropathogenic Escherichia coli

The GenBank accession numbers for the DNA sequences of the rpoS loci in E. coli strains HU734 and CFT073 are AF275947 and AF270497, respectively.

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