MULTICOPY VECTORS CARRYING THE KLEBSIELLA-PNEUMONIAE NIFA GENE DO NOTENHANCE THE NODULATION COMPETITIVENESS OF SINORHIZOBIUM-MELILOTI ON ALFALFA

It has been reported that Sinorhizobium meliloti strains harboring Inc Q and IncP multicopy vectors containing constitutively expressed Klebs iella pneumoniae nifA exhibit an increase in nodulation competitivenes s on alfalfa (J. Sanjuan and J. Olivares, Mel. Plant-Microbe Interact. 4:365-369, 1991), In our efforts to understand the mechanisms involve d, in this work, we have found that the observed enhancement on nodula tion competitiveness by IncQ derivatives carrying K. pneumoniae nifA w as not dependent on the plasmid-borne nifA activity but on the sensiti vity of nonresistant strains to the streptomycin carried over from gro wth cultures. Furthermore, it was also determined that the nifA of K. pneumoniae on an IncP vector does not have an effect on competitivenes s.