Table 1.

Strains and plasmids used in this study

Strain or plasmidCharacteristics and (or) derivationsSource or reference
Strains
E. coliDH5α supE44 lacU169(φ80lacZΔM15) hsdR17 recA1 endA1 gyrA96 thi-1 relA1 8a
S. meliloti
  1022Smr; wild type 20a
  C22Kmr; S. meliloti 1021ndiB::Tn51063a 23
  12,C-4Tcr Kmr; C22tspO::Tn1721 This study
  R-C22Tcr; S. meliloti 1021tspO::Tn1721 This study
  5001 ntrC::Tn5; Smr Kmr 37
Plasmids
 pRK2013Kmr; triparental mating helper, ColE1 replication, Tra+ 6a
 pJOE105Tcr suicide vector, contains transposon Tn1721 32a
 pTB93FPtrp-GFP-S65T in pMB393; Spr 8
 pBluescript II SKApr; cloning and sequencing vectorStratagene, La Jolla, Calif.
 pLAFR1Broad host range; Tcr IncP Mob+ Tra 7a
 pC22Kmr; EcoRI transposon recovery from strain C22This study
 pC22luxSprKmr; entire 12.2-kb EcoRI fragment of pC22 inserted into pTB93This study
 pBSRApr;HindIII transposon Tn1721 recovery from strain 12,C-4This study
 pLtspOTcr; clone containing tspO locus from pLAFR1 S. melilotilibrary 6
 pTtspOSpr;ppuMI-SalI fragment of pLtspO containingtspO ORF from S. meliloti inserted into pTB93This study
 pUI1126Tcr; pRK415 containingtspO under control of PrrnB 48
 pRstspOSpr; BamHI-KpnI fragment containing tspO gene from plasmid pUI1126 inserted into pTB93This study