FIG. 7.

(A) Buffering of growing cultures alters OHHL turnover. Cultures of MS1 were grown in LB medium buffered with 100 mM potassium phosphate at pH 6.7 (circles) or at pH 7.7 (squares). The OHHL levels (solid symbols) and pH values (open symbols) at each time point are shown. (B) pH-dependent degradation of OHHL in conditioned medium. Supernatants taken throughout the growth curve of GB7 were buffered with 200 mM potassium phosphate at pH 6.8 (filled symbols) or pH 8.3 (open symbols) either before (circles) or after (triangles) an 18 h of incubation at 30°C. The residual OHHL concentration in each set of supernatants is shown. Error bars represent the standard error of the mean from two independent cultures.