Updated project metadata. Francisella possesses a non-canonical T6SS that is essential for efficient phagosomal escape and access to the cytosol of infected macrophages. Using a global and site-specific phosphoproteomic analysis of Francisella we identified here a unique phosphorylation site on IglB, the TssC homologue and a key component of the T6SS contractile sheath. Phosphorylation of the sheath may constitute a previously unrecognized mechanism contributing to the dynamics of assembly-disassembly of the T6SS.