E. coli Are Undetectable After Exposure to V. cholerae. Fluorescence
microscopy was used to determine the state of E. coli before and
after exposure to V. cholerae strains V52 and V52ΔvasK, where
V. cholerae and E. coli were distinguishable by fluorescence at
separate wavelengths. V. cholerae and E. coli were incubated on
Luria–Bertani medium (LB) agar for 4 h, at which time bacteria
were harvested, washed, fixed, and inspected by fluorescence
microscopy. E. coli was visibly detectable before exposure to V52
or V52ΔvasK, but was completely absent from the field of view
after 4 h of exposure to V52 (Fig. 3A). The loss of fluorescent
signal is indicative of cell lysis as released mCherry would have
been lost during the washing step following the incubation on
LB-agar plates. The lysis of E. coli can be attributed to the T6SS
because the V52ΔvasK treatment had no effect on the visualization
of E. coli (Fig. 3B).