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Infection and Immunity, April 2001, p. 2198-2210, Vol. 69, No. 4
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

Michael W. Ferguson,^1,* Jill A. Maxwell,^1, Timothy S. Vincent,² Jack da Silva,³ and Joan C. Olson²

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.

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^* 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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Infection and Immunity, April 2001, p. 2198-2210, Vol. 69, No. 4
0019-9567/01/$04.00+0   DOI: 10.1128/IAI.69.4.2198-2210.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

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