Role of Vfr in regulating exotoxin A production by Pseudomonas aeruginosa

1 Department of Biological Sciences, Texas Tech University, MS3131, Lubbock, TX 79409, USA 2 Department of Microbiology and Immunology, School of Medicine, Texas Tech University Health Sciences Center, 3601 4th Street, Lubbock, TX 79430, USA Pseudomonas aeruginosa exotoxin A (ETA) production depends on the virulence-factor regulator Vfr. Recent evidence indicates that the P. aeruginosa iron-starvation sigma factor PvdS also enhances ETA production through the ETA-regulatory gene regA . Mutants defective in vfr , regA and pvdS , plasmids that overexpress these genes individually and lacZ transcriptional/translational fusion plasmids were utilized to examine the relationship between vfr , regA and pvdS in regulating P. aeruginosa ETA production. ETA concentration and regA expression were reduced significantly in PAO vfr , but pvdS expression was not affected. Overexpression of Vfr produced a limited increase in ETA production in PAO pvdS , but not PAO regA . Additionally, overexpression of either RegA or PvdS did not enhance ETA production in PAO vfr . RT-PCR analysis showed that iron did not affect the accumulation of vfr mRNA in PAO1. These results suggest that: (i) Vfr enhances toxA expression in PAO1 both directly and indirectly through regA , but not through pvdS ; (ii) vfr expression is not regulated by iron; and (iii) both Vfr and PvdS cooperate in the presence of RegA to achieve a maximum level of toxA expression. Correspondence Abdul N. Hamood abdul.hamood{at}ttuhsc.edu Abbreviations: ETA, exotoxin A; RNAP, RNA polymerase Present address: Rawls College of Business Administration, Texas Tech University, MS2101, Lubbock, TX 79409, USA. A supplementary figure showing that overexpression of Vfr does not enhance ETA production in PAO regA is available with the online version of this paper.