Bacterial strains, plasmids, and growth conditions.
Microbiological materials used in the present work are listed in Table Table1.1. Escherichia coli was grown at 37°C on Luria-Bertani (LB) or M9 medium (29) supplemented with appropriate antibiotics, and S. meliloti 1021 was grown in GTS medium (20). Tests for rhizosphere growth and colonization of alfalfa roots were done as reported previously (33).