The acute diarrheal disease cholera is caused by the marine bacterium
Vibrio cholerae. A type VI secretion system (T6SS), which is
structurally similar to the bacteriophage cell-puncturing device, has
been recently identified in V. cholerae and is used by this organism to
confer virulence toward phagocytic eukaryotes, such as J774 murine
macrophages and Dictyosteliumdiscoideum.We tested the interbacterial
virulence of V. cholerae strain V52, an O37 serogroup with
a constitutively active T6SS. V52 was found to be highly virulent
toward multiple Gram-negative bacteria, including Escherichia
coli and Salmonella Typhimurium, and caused up to a 100,000-fold
reduction in E. coli survival. Because the T6SS-deficient mutants
V52ΔvasK and V52ΔvasH showed toxicity defects that could be complemented,
virulence displayed by V. cholerae depends on a functional
T6SS. V. cholerae V52 and strains of the O1 serogroup were
resistant to V52, suggesting that V. cholerae has acquired immunity
independently of its serogroup. We hypothesize that the T6SS, in
addition to targeting eukaryotic host cells, confers toxicity toward
other bacteria, providing a means of interspecies competition to
enhance environmental survival. Thus, the V. cholerae T6SS may
enhance the survival of V. cholerae in its aquatic ecosystem during
the transmission of cholera and between epidemics.