Comparison of the exoS gene and protein expression in soil and clinical isolates of Pseudomonas aeruginosa

Exoenzyme S (ExoS) is translocated into eukaryotic cells by the type In: se cretory process and has been hypothesized to function in conjunction with o ther virulence factors in the pathogenesis of Pseudomonas aeruginosa. To ga in further understanding of how ExoS might contribute to P. aeruginosa surv ival and virulence, ExoS expression and the structural gene sequence were d etermined in P. aeruginosa soil isolates and compared with ExoS of clinical isolates. Significantly higher levels of ExoS ADP-ribosyltransferase (ADPR T) 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 productio n of ExoS having a higher specific activity. ExoS structural gene sequence comparisons found the gene to be highly conserved among soil and clinical i solates with the greatest number of nonsynonymous substitutions occurring w ithin the region of ExoS encoding GAP function. The lack of amino acid chan ges in the ADPRT region in association with a higher specific activity impl ies that other factors produced by P. aeruginosa or residues outside the AD PRT 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 setti ngs, the loss of ExoS expression is favored.