Killing Requires Cell–Cell Contact. On the basis of the current model
for T6SS, substrates pass directly from the secreting cell into the
cytoplasm of the target cell. To test whether T6SS-mediated antimicrobial
activity requires contact between V. cholerae and
E. coli, survival was measured with a 0.22-μm filter between V52
predator and E. coli prey to allow the passage of molecules but
not bacterial cells (Fig. 4). The presence of the filter abrogated
killing, made apparent by an increase in E. coli survival and cfu
per milliliter values that were indistinguishable from those with
no predator, V52ΔvasK, or E. coli as predator (Fig. 4).