to be highly virulent toward various Gram-negative bacteria including
E. coli K-12 MG1655, enterohemorrhagic E. coli (EHEC)
O157:H7, enteropathogenic E. coli (EPEC) E2348/69, Salmonella
Typhimurium, and Citrobacter rodentium, whereas virulence was
abrogated in the T6SS-deficient mutant V52ΔvasK (Fig. 1 A and
B). P. aeruginosa PAO1 was not susceptible to V52 bacterial
virulence (Fig. 1A). V52 did not display T6SS-dependent virulence
toward any of the Gram-positive species tested (Fig. S1A).
Although V52 was virulent toward Bacillus subtilis, toxicity was
not dependent on the T6SS because V52ΔvasK retained a wildtype
level of virulence (Fig. S1A). This result is not surprising
because V. cholerae produces a variety of bacteriocins that we
suspect are toxic toward B. subtilis (15). Yeast prey Candida
albicans and Saccharomyces cerevisiae grew well in the presence of
both V52 and V52ΔvasK (Fig. S1 B and C). These results suggest
that the T6SS enables V. cholerae to kill bacteria with a host range
specificity limited to certain Gram-negative bacteria.