FIG 3.

SitA toxins are functionally modular. (A) Schematic of three SitAI proteins used to construct four chimeras. The toxin domains are SitA3^Mx Cdi_tRNase (PF18451), SitA3^Mf1 Tox-RNase-5 (PF15648), and SitA5^Mf1 HNH nuclease. (B) Colony merger assays where the respective indicator (sensitive) strains (left) were spotted adjacent to test strains expressing the indicated sitAI loci (right) and incubated for 2 days. Green arrow, merging colonies; red arrow, demarcation. Bar, 5 mm. (C) Swarm inhibition by chimeras and parent sitAI alleles expressed in isogenic nonmotile strains tested against a motile indicator (WT) strain. The left panel shows the no-inhibition control; the next two panels show parent sitAI allele controls. Bar, 5 mm. (D) Competition indices of chimeras and parent sitAI alleles done with fluorescently labeled target cells (see Fig. S5A in the supplemental material). The ratios of green fluorescent protein (GFP)-labeled target cells (WT) (left) and ΔsitBAI3^Mx (removes endogenous sitI3^Mx) cells (right) were plotted against unlabeled inhibitor cells (bottom) (note the negative controls on the left). Standard deviations (SDs) from three biological replicates are shown.