TABLE 1.

Bacterial strains and plasmids

Strain or plasmid	Relevant characteristicsa	Reference
Rhizobium etli
CE3	Strr derivative of CFN42	16
CFN2012	ntrC::Tn5 mutant of CE3	15
Plasmids
cGD101	Cosmid clone from R etli symbiotic plasmid	8
pMSfixc	pTR101 containing the B. japonicum fixNOQP operon fused to the nptII promoter	8
pMP220	Transcriptional lacZ fusion vector; Tcr	24
pOLfix10	pMP220::1.1-kb PstI fragment; fixN-lacZ gene fusion	This work

^aStr, streptomycin; Tc, tetracycline.