TABLE 1.

Bacterial strains used in this study

Strain	Relevant characteristics	Reference or source
Rhizobium leguminosarum 8401	Streptomycin-resistant mutant of Sym− strain 8400, Srr	12
R. leguminosarum 8401 (pRL1JI)	8401 containing self-transmissible Sym plasmid pRL1JI of R. leguminosarum bv. viciae, pRL1JI represses normal synthesis of (3-OH)C14:1HSL and inhibits cell growth in the presence of this AHL, Srr	11
R. leguminosarum 8401(pIJ1089)	8401 containing a 30-kb cosmid fragment of pRL1JI that includes all of the known rhi genes, used as a source of C6HSL, Srr Tcr	5
R. leguminosarum 14482Sr	Streptomycin-resistant mutant of R. leguminosarum bv. phaseoli ATCC 14482, used as a source of (3-O)C8HSL, C8HSL, and (3-OH)C14:1HSL, Srr	This study
R. leguminosarum 8401(pIJ1642)	8401 with plasmid pIJ1089 containing a Tn3::lacZ reporter fusion in rhiA that is activated in response to C6HSL, Srr Tcr	6
R. leguminosarum 8401(pRL1JI/pIJ1769)	8401 containing both pRL1JI and a rhiA′::lacZ reporter plasmid (pIJ1769) that is activated in response to (3-OH)C14:1HSL, Srr Tcr	9
Agrobacterium tumefaciens NT1(pDCI41E33)	Ti− strain that does not produce AHL, plasmid pDCI41E33 contains the luxR homolog traR and a traG::lacZ reporter that is activated in response to diverse AHLs, Kmr	S. K. Farrand
Chromobacterium violaceum CV0blu(pSB403)	Tn5 mutant strain that does not produce AHL, contains the luxR homolog cviR that activates violacein synthesis in response to diverse AHLs, plasmid pSB403 also encodes LuxR from V. fischeri, Cpr Tcr	3