Identification of the wbtF gene as a cytotoxicity-associated factor in Francisella novicida infection

A total of thirteen mutants with attenuated cytotoxicity were isolated, and their responsible genes were identified. They are <i>figE, slt, fopA, iglC, igID, iglF, iglI, pdpB, pdpA, ampG</i>, <i>wbtF</i>, and one unnamed gene (FTN_0096). We focused on the <i>wbtF</i> gene. The <i>F. novicida</i> wild-type (WT) strain showed intracellular replication in HeLa-FcγRII and THP-1 cells, but the number of intracellular <i>wbtF</i> mutants decreased. The <i>wbtF</i> mutant could not escape from phagolysosomes in the initial phases of infection and was digested within the lysosome. The <i>wbtF</i> mutant was also detected in the mitochondria and the Golgi complex. The cytokine response induced by <i>wbtF</i> mutant was comparable to that of the WT strain. These findings indicate that <i>wbtF</i> is important for the intracellular replication of <i>F. novicida</i>.