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Infection and Immunity, July 2008, p. 2852-2861, Vol. 76, No. 7
0019-9567/08/$08.00+0     doi:10.1128/IAI.01726-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Type IV Pili in Francisella tularensis: Roles of pilF and pilT in Fiber Assembly, Host Cell Adherence, and Virulence

Subhra Chakraborty,¹ Michael Monfett,¹ Tamara M. Maier,² Jorge L. Benach,¹ Dara W. Frank,² and David G. Thanassi^1*

Center for Infectious Diseases, Department of Molecular Genetics and Microbiology, Stony Brook University, Stony Brook, New York 11794-5120,¹ Department of Microbiology and Molecular Genetics, Medical College of Wisconsin, Milwaukee, Wisconsin 53226²

Received 21 December 2007/ Returned for modification 28 January 2008/ Accepted 6 April 2008

Francisella tularensis, a highly virulent facultative intracellular bacterium, is the causative agent of tularemia. Genome sequencing of all F. tularensis subspecies revealed the presence of genes that could encode type IV pili (Tfp). The live vaccine strain (LVS) expresses surface fibers resembling Tfp, but it was not established whether these fibers were indeed Tfp encoded by the pil genes. We show here that deletion of the pilF putative Tfp assembly ATPase in the LVS resulted in a complete loss of surface fibers. Disruption of the pilT putative disassembly ATPase also caused a complete loss of pili, indicating that pilT functions differently in F. tularensis than in model Tfp systems such as those found in Pseudomonas aeruginosa and Neisseria spp. The LVS pilF and pilT mutants were attenuated for virulence in a mouse model of tularemia by the intradermal route. Furthermore, although absence of pili had no effect on the ability of the LVS to replicate intracellularly, the pilF and pilT mutants were defective for adherence to macrophages, pneumocytes, and hepatocytes. This work confirms that the surface fibers expressed by the LVS are encoded by the pil genes and provides evidence that the Francisella pili contribute to host cell adhesion and virulence.

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* Corresponding author. Mailing address: 242 Center for Infectious Diseases, Stony Brook University, Stony Brook, NY 11794-5120. Phone: (631) 632-4549. Fax: (631) 632-4294. E-mail: david.thanassi{at}stonybrook.edu

Published ahead of print on 21 April 2008.

Editor: A. Camilli

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Infection and Immunity, July 2008, p. 2852-2861, Vol. 76, No. 7
0019-9567/08/$08.00+0     doi:10.1128/IAI.01726-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

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