Genome-Wide Identification ofFrancisella tularensisVirulence Determinants

Abstract

Francisella tularensisis a gram-negative pathogen that causes life-threatening infections in humans and has potential for use as a biological weapon. The genetic basis of theF. tularensisvirulence is poorly understood. This study screened a total of 3,936 transposon mutants of the live vaccine strain for infection in a mouse model of respiratory tularemia by signature-tagged mutagenesis. We identified 341 mutants attenuated for infection in the lungs. The transposon disruptions were mapped to 95 different genes, virtually all of which are also present in the genomes of otherF. tularensisstrains, including human pathogenicF. tularensisstrain Schu S4. A small subset of these attenuated mutants carried insertions in the genes encoding previously known virulence factors, but the majority of the identified genes have not been previously linked toF. tularensisvirulence. Among these are genes encoding putative membrane proteins, proteins associated with stress responses, metabolic proteins, transporter proteins, and proteins with unknown functions. Several attenuated mutants contained disruptions in a putative capsule locus which partially resembles the poly-γ-glutamate capsule biosynthesis locus ofBacillus anthracis, the anthrax agent. Deletional mutation analysis confirmed that this locus is essential forF. tularensisvirulence.