FIG. 5.

PhzR responds only to the 3-OH-hexanoyl-HSL present in culture supernatants of P. fluorescens 2-79. An ethyl acetate extract of a culture supernatant of P. fluorescens 2-79 grown to late exponential phase in King's medium B, as well as several standard compounds, was chromatographed, and the TLC plate was overlaid with a mixture of P. fluorescens 1855(pSF105, pSF107) and C. violaceum CV026blu as described in Materials and Methods. The blue spots represent acyl-HSLs detected by the P. fluorescens phzA::lacZ reporter, while the purple spots correspond to species detected by C. violaceum. Lanes contain samples of (1) extract from a culture supernatant of P. fluorescens 2-79 and pure standards of (2) N-(3-OH-octanoyl)-HSL, (3) N-(3-OH-hexanoyl)-HSL, (4) N-hexanoyl-HSL, and (5) a mixture of N-(3-OH-hexanoyl)-HSL and N-hexanoyl-HSL.