FIG. 3.

Endogenously produced indole acts as a signal to stimulate the expression of vpsL in recipient cells. (A) In the coculture experiment, an indole-negative donor strain, S2150 [I(−)], does not upregulate vpsL::lacZ expression in the reporter strain S9149 (gray bar), while the indole-positive donor strain S2148 [I(+)] can complement vpsL::lacZ expression to similar levels as when 0.5 mM indole (I) is added exogenously (white bars). (B) The same upregulation by indole is seen when the S9149 reporter strain is grown in conditioned medium grown from indole-positive supernatant from S2148 (SI+) and indole-negative supernatant from S2150 (SI−) conditions. Growth of S9149 in LB medium alone also did not stimulate vpsL::lacZ upregulation. For the coculture experiment Miller units are normalized to the percentage of S9149 cells from the total OD (see Materials and Methods). Error bars represent 1 standard deviation from the mean of three biological replicates for each strain.