Molecular complexity orchestrates modulation of phagosome biogenesis and escape to the cytosol of macrophages by Francisella tularensis
Article first published online: 7 MAY 2010
© 2010 Society for Applied Microbiology and Blackwell Publishing Ltd
Volume 12, Issue 9, pages 2559–2586, September 2010
How to Cite
Asare, R. and Abu Kwaik, Y. (2010), Molecular complexity orchestrates modulation of phagosome biogenesis and escape to the cytosol of macrophages by Francisella tularensis. Environmental Microbiology, 12: 2559–2586. doi: 10.1111/j.1462-2920.2010.02229.x
- Issue published online: 3 SEP 2010
- Article first published online: 7 MAY 2010
- Received 23 February, 2010; accepted 25 February, 2010.
Vol. 13, Issue 12, 3310, Article first published online: 28 NOV 2011
Upon entry of Francisella tularensis to macrophages, the Francisella-containing phagosome (FCP) is trafficked into an acidified late endosome-like phagosome with limited fusion to the lysosomes followed by rapid escape into the cytosol where the organism replicates. Although the Francisella Pathogenicity Island (FPI), which encodes a type VI-like secretion apparatus, is required for modulation of phagosome biogenesis and escape into the cytosol, the mechanisms involved are not known. To decipher the molecular bases of modulation of biogenesis of the FCP and bacterial escape into the macrophage cytosol, we have screened a comprehensive mutant library of F. tularensis ssp. novicida for their defect in proliferation within human macrophages, followed by characterization of modulation of phagosome biogenesis and bacterial escape into the cytosol. Our data show that at least 202 genes are required for intracellular proliferation within macrophages. Among the 125 most defective mutants in intracellular proliferation, we show that the FCP of at least 91 mutants colocalize persistently with the late endosomal/lysosomal marker LAMP-1 and fail to escape into the cytosol, as determined by fluorescence-based phagosome integrity assays and transmission electron microscopy. At least 34 genes are required for proliferation within the cytosol but do not play a detectable role in modulation of phagosome biogenesis and bacterial escape into the cytosol. Our data indicate a tremendous adaptation and metabolic reprogramming by F. tularensis to adjust to the micro-environmental and nutritional cues within the FCP, and these adjustments play essential roles in modulation of phagosome biogenesis and escape into the cytosol of macrophages as well as proliferation in the cytosol. The plethora of the networks of genes that orchestrate F. tularensis-mediated modulation of phagosome biogenesis, phagosomal escape and bacterial proliferation within the cytosol is novel, complex and involves an unusually large portion of the genome of an intracellular pathogen.