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Infection and Immunity, April 2001, p. 2198-2210, Vol. 69, No. 4
Biology Department, Coastal Carolina
University, Conway, South Carolina 29528-60541;
Department of Pathology and Laboratory Medicine, Medical
University of South Carolina, Charleston, South Carolina
294252; and Department of Biology,
East Carolina University, Greenville, North Carolina
278583
Received 2 August 2000/Returned for modification 6 October
2000/Accepted 28 December 2000
Exoenzyme S (ExoS) is translocated into eukaryotic cells by the
type III secretory process and has been hypothesized to function in
conjunction with other virulence factors in the pathogenesis of
Pseudomonas aeruginosa. To gain further understanding of
how ExoS might contribute to P. aeruginosa survival and
virulence, ExoS expression and the structural gene sequence were
determined in P. aeruginosa soil isolates and compared with
ExoS of clinical isolates. Significantly higher levels of ExoS
ADP-ribosyltransferase (ADPRT) activity were detected in culture
supernatants of soil isolates compared to those of clinical isolates.
The higher levels of ADPRT activity of soil isolates reflected both the
increased production of ExoS and the production of ExoS having a higher specific activity. ExoS structural gene sequence
comparisons found the gene to be highly conserved among soil and
clinical isolates, with the greatest number of nonsynonymous
substitutions occurring within the region of ExoS encoding GAP
function. The lack of amino acid changes in the ADPRT region in
association with a higher specific activity implies that other factors
produced by P. aeruginosa or residues outside the ADPRT
region are affecting ExoS ADPRT activity. The data are consistent with
ExoS being integral to P. aeruginosa survival in the soil
and suggest that, in the transition of P. aeruginosa from
the soil to certain clinical settings, the loss of ExoS expression is favored.
0019-9567/01/$04.00+0 DOI: 10.1128/IAI.69.4.2198-2210.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Comparison of the exoS Gene and Protein
Expression in Soil and Clinical Isolates of Pseudomonas
aeruginosa

*
Corresponding author. Mailing address: Biology
Department, Coastal Carolina University, P.O. Box 261954, Conway, SC
29528-6054. Phone: (843) 349-2214. Fax: (843) 349-2201. E-mail:
ferguson{at}coastal.edu.
Present address: Department of Microbiology and Immunology, East
Carolina University School of Medicine, Greenville, NC 27858.
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