Infection and Immunity, June 2000, p. 3067-3073, Vol. 68, No. 6
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Copyright © 2000, American Society for Microbiology. All rights reserved.


Department of Biochemistry, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China
Received 14 January 2000/Returned for modification 21 February 2000/Accepted 10 March 2000
DNA sequencing upstream of the Salmonella enterica serovar Typhi pilV and rci genes previously identified in the ca. 118-kb major pathogenicity island (X.-L. Zhang, C. Morris, and J. Hackett, Gene 202:139-146, 1997) identified a further 10 pil genes apparently forming a pil operon. The product of the pilS gene, prePilS protein (a putative type IVB structural prepilin) was purified, and an anti-prePilS antiserum was raised in mice. Mutants of serovar Typhi either lacking the whole pil operon or with an insertion mutation in the pilS gene were constructed, as was a strain in which the pilN to pilV genes were driven by the tac promoter. The pil+ strains synthesized type IVB pili, as judged by (i) visualization in the electron microscope of thin pili in culture supernatants of one such strain and (ii) the presence of PilS protein (smaller than the prePilS protein by removal of the leader peptide) on immunoblotting of material pelleted by high-speed centrifugation of either the culture supernatant or sonicates of pil+ strains. Control pil mutants did not express the PilS protein. A pilS mutant of serovar Typhi entered human intestinal INT407 cells in culture to levels only 5 to 25% of those of the wild-type strain, and serovar Typhi entry was strongly inhibited by soluble prePilS protein (50% inhibition of entry at 1.4 µM prePilS).
Present address: Department of Animal and Avian Sciences,
University of Maryland, College Park, MD 20742.
Present address: Shanghai Research Centre of Biotechnology,
Chinese Academy of Sciences, Shanghai 200233, China.
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