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Infection and Immunity, October 1999, p. 5106-5116, Vol. 67, No. 10
0019-9567/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Genomic Subtractive Hybridization and Selective Capture of Transcribed Sequences Identify a Novel Salmonella typhimurium Fimbrial Operon and Putative Transcriptional Regulator That Are Absent from the Salmonella typhi Genome

Brian J. Morrow, James E. Graham,dagger and Roy Curtiss III*

Department of Biology, Washington University, St. Louis, Missouri 63130

Received 24 March 1999/Returned for modification 29 June 1999/Accepted 29 July 1999

Salmonella typhi, the etiologic agent of typhoid fever, is adapted to the human host and unable to infect nonprimate species. The genetic basis for host specificity in S. typhi is unknown. The avirulence of S. typhi in animal hosts may result from a lack of genes present in the broad-host-range pathogen Salmonella typhimurium. Genomic subtractive hybridization was successfully employed to isolate S. typhimurium genomic sequences which are absent from the S. typhi genome. These genomic subtracted sequences mapped to 17 regions distributed throughout the S. typhimurium chromosome. A positive cDNA selection method was then used to identify subtracted sequences which were transcribed by S. typhimurium following macrophage phagocytosis. A novel putative transcriptional regulator of the LysR family was identified as transcribed by intramacrophage S. typhimurium. This putative transcriptional regulator was absent from the genomes of the human-adapted serovars S. typhi and Salmonella paratyphi A. Mutations within this gene did not alter the level of S. typhimurium survival within macrophages or virulence within mice. A subtracted genomic fragment derived from the ferrichrome operon also hybridized to the intramacrophage cDNA. Nucleotide sequence analysis of S. typhimurium and S. typhi chromosomal sequences flanking the ferrichrome operon identified a novel S. typhimurium fimbrial operon with a high level of similarity to sequences encoding Proteus mirabilis mannose-resistant fimbriae. The novel fimbrial operon was absent from the S. typhi genome. The absence of specific genes may have allowed S. typhi to evolve as a highly invasive, systemic human pathogen.

* Corresponding author. Mailing address: Department of Biology, Washington University, One Brookings Drive, Campus Box 1137, St. Louis, MO 63130-4899. Phone: (314) 935-6819. Fax: (314) 935-7246. E-mail: rcurtiss{at}biodec.wustl.edu.

dagger Present address: Department of Medicine, Vanderbilt University, Nashville, TN 37232.

Infection and Immunity, October 1999, p. 5106-5116, Vol. 67, No. 10
0019-9567/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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