Figure 2.

A predicted ART domain-containing substrate of the T6SS is an antibacterial toxin that promotes competitiveness of S. proteamaculans. (A) Viable E. coli cells recovered from plating cultures carrying plasmids expressing the indicated proteins on inducing media (c.f.u. = colony forming units). (B) and (C) Representative micrographs of E. coli cells expressing Tre1_tox (B) or Tre1_tox ^E415Q (C). Frames were acquired 200 min after induction of protein expression. Scale bar = 2 μm. (D) Relative competitiveness of the indicated donor (“D”) and recipient (“R”) strains of S. proteamaculans grown in co-culture on a solid surface for 6 h. Competitive index was determined by comparing final and initial c.f.u. ratios of the two strains. (E) Interspecies competition experiments between the indicated S. proteamaculans donor strains grown in co-culture with the noted E. coli recipients, quantified as in D. Data in A, D and E are represented as means ± standard deviation (SD). Asterisks in D and E indicate statistically significant differences between competitive indices of a given donor strain toward the indicated recipients (p<0.05). For experiments shown in A, D and E, n ≥ 3. See also Figure S1 and Videos S1 and S2.