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Infection and Immunity, October 2009, p. 4446-4454, Vol. 77, No. 10
0019-9567/09/$08.00+0     doi:10.1128/IAI.00822-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Nitrite Reductase NirS Is Required for Type III Secretion System Expression and Virulence in the Human Monocyte Cell Line THP-1 by Pseudomonas aeruginosa{triangledown}

Nadine E. Van Alst,1 Melanie Wellington,2 Virginia L. Clark,1 Constantine G. Haidaris,1 and Barbara H. Iglewski1*

Department of Microbiology and Immunology,1 Department of Pediatrics, University of Rochester Medical Center, Rochester, New York 146422

Received 23 July 2009/ Returned for modification 24 July 2009/ Accepted 28 July 2009

The nitrate dissimilation pathway is important for anaerobic growth in Pseudomonas aeruginosa. In addition, this pathway contributes to P. aeruginosa virulence by using the nematode Caenorhabditis elegans as a model host, as well as biofilm formation and motility. We used a set of nitrate dissimilation pathway mutants to evaluate the virulence of P. aeruginosa PA14 in a model of P. aeruginosa-phagocyte interaction by using the human monocytic cell line THP-1. Both membrane nitrate reductase and nitrite reductase enzyme complexes were important for cytotoxicity during the interaction of P. aeruginosa PA14 with THP-1 cells. Furthermore, deletion mutations in genes encoding membrane nitrate reductase ({Delta}narGH) and nitrite reductase ({Delta}nirS) produced defects in the expression of type III secretion system (T3SS) components, extracellular protease, and elastase. Interestingly, exotoxin A expression was unaffected in these mutants. Addition of exogenous nitric oxide (NO)-generating compounds to {Delta}nirS mutant cultures restored the production of T3SS phospholipase ExoU, whereas nitrite addition had no effect. These data suggest that NO generated via nitrite reductase NirS contributes to the regulation of expression of selected virulence factors in P. aeruginosa PA14.

* Corresponding author. Mailing address: Department of Microbiology and Immunology, Box 672, University of Rochester Medical Center, 601 Elmwood Ave., Rochester, NY 14642. Phone: (585) 275-3402. Fax: (585) 473-9573. E-mail: bigl{at}mail.rochester.edu

{triangledown} Published ahead of print on 3 August 2009.

Editor: A. J. Bäumler

Infection and Immunity, October 2009, p. 4446-4454, Vol. 77, No. 10
0019-9567/09/$08.00+0     doi:10.1128/IAI.00822-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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