FIG 1.

B. subtilis expands asymmetrically toward S. plymuthica. (A) Time course of interaction between B. subtilis and S. plymuthica, with no contact (24 h), initial contact (48 h), and engulfment (72 h). Top-down images of biofilm colonies grown on solid biofilm-inducing medium are shown; scale bar = 0.2 cm. (B) Quantification of asymmetric expansion of B. subtilis biofilm toward S. plymuthica biofilm. Wild-type (WT) B. subtilis and the indicated mutant strains were inoculated near S. plymuthica at different distances as indicated in the key (in cm), and incubated at 30°C for 3 days. The expansion ratio was defined as the ratio between the radius from the center of the B. subtilis biofilm to the S. plymuthica colony and the radius extending to the opposite side of the biofilm. B. subtilis biofilm grown alone served as a control (Ctr). RU, relative units. (C) Quantification of asymmetric expansion of B. subtilis biofilm toward live S. plymuthica, the supernatant of S. plymuthica, or dead S. plymuthica cells. (D) Top-down images of B. subtilis biofilm expanding toward PBS (negative control), indicated amounts of isolated S. plymuthica (S.p) EPS, or S. plymuthica colony (positive control). (E) Quantification of asymmetric expansion of B. subtilis biofilm toward S. plymuthica biofilm. WT B. subtilis and the indicated mutant strains were inoculated near S. plymuthica at different distances, as indicated by the key, and incubated at 30°C for 3 days. This experimental series was done in parallel to the experiment in panel B; therefore, the same WT control is used. **, P < 0.005 based on a two-tailed Student's t test of the entire indicated measurement series. Error bars represent standard deviations. All experiments were performed at least 3 times with at least two technical repeats.