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. Author manuscript; available in PMC: 2012 Jan 1.
Published in final edited form as: Mol Microbiol. 2010 Nov 2;79(1):166–179. doi: 10.1111/j.1365-2958.2010.07436.x

Figure 4.

Figure 4

The HSL and C4HSL Quorum sensing signals are required for biosurfactant secretion, yet their addition to the medium addition does not cause over secretion. (A) Diagram of the hierarchical quorum sensing system lasR/lasI - rhlR/rhlI regulating expression of the rhlAB operon. (B) Mutants that are unable to synthesize either of the two quorum sensing signals (lasI− lacks synthesis of HSL and rhlI− lacks synthesis of C4HSL) do not secrete biosurfactants in the absence of exogenous signal. These signal dose response curves allowed measuring the autoinducer concentrations needed to restitute WT level of rhamnolipid secretion: 1 μM for HSL and 5 μM for C4HSL. (C–E) Adding saturating amounts of either signal (C, D) or both together (E) to growth media did not visibly affect growth of the wild-type. (F) The rhamnolipids measured at the end of growth also showed no significant difference (P > 0.03, P > 0.3 and P > 0.1 respectively for HSL, C4HSL and both signals when compared to WT grown without signal addition).