Fig. S3.

T6S-dependent strain dynamics in vivo. (A and B) A B. fragilis^N tssC strain lacking both E/I pairs [nonimmune (n.i.)] was introduced into germ-free mice in the presence of B. fragilis^N tssC (A) or WT (B) B. fragilis^N at the indicated starting ratios of D to S cells. *P < 0.05 between nonimmune populations in each group (n = 5 mice per group; representative of two independent trials); error bars indicate ± SD. (C) B. fragilis^N targets susceptible cells in the large intestine but not the small intestine. Luminal contents from small intestine (SI) or large intestine segments of mice in Fig. 5A were collected for analysis by qPCR on day 15 of the experiment (Dataset S1, Table S5). *P < 0.05 between nonimmune populations in each group (n = 5 mice per group; representative of two independent trials); error bars indicate ± SD. (D) Nonimmune B. fragilis^N (Bf^N n.i.) is not effectively killed by WT B. fragilis^N in liquid culture. (E) B. fragilis T6S activity requires cell contact. B. fragilis^N WT or tssC donor strains were cocultured on solid media with a nonimmune mutant B. fragilis^N recipient on a 0.2-µm filter. In i and ii, a second 0.2-µm filter was placed between donor and recipient strains, whereas in iii, the second filter was omitted. Cocultures with WT B. fragilis^N are shown, and data were normalized to coculture experiments with the T6S-deficient tssC mutant B. fragilis^N (dotted line). *P < 0.05 between WT and tssC competitions.