Figure 1.

Visualization of Distinct Components within an Active Type VI Secretion System in Serratia marcescens

(A) Cartoon depiction of the T6SS with the components visualized in this study highlighted in red. The fourteen core components and one accessory component, Fha, are labeled. Cytoplasm (cyto), periplasm (peri), inner membrane (IM), and outer membrane (OM) of the secreting cell are indicated.

(B) T6SS-dependent secretion of Hcp and the effector Ssp1 by S. marcescens Db10 (WT) and derivatives expressing fusions of mCherry to the C terminus of TssB (TssB-mCh), TssH (TssH-mCh), TssJ (TssJ-mCh), or TssL (TssL-mCh). The T6SS inactive mutant ΔtssE is a negative control, and cellular (cell) and secreted (sec) fractions were subjected to immunoblotting using anti-Hcp and anti-Ssp1 antisera as indicated.

(C) T6SS-dependent antibacterial activity of fluorescent reporter strains against P. fluorescens target cells. Recovery of target cells following a 4-hr co-culture with the attacking strains of S. marcescens indicated; points show mean ± SEM (n = 4).

(D–G) Representative images of cells expressing TssB-mCh (D), TssH-mCh (E), TssJ-mCh (F), or TssL-mCh (G). Upper panels: DIC images; lower panels: corresponding fluorescence images (mCherry channel); scale bar, 1 μm.

See also Figure S1.