Method for selecting mutants of legume-nodulating bacteria enhanced in competition

摘要

Methods for the isolation of mutant rhizobial strains with improved competition of nodulation (Comp.sup.+) is presented. Mutants are selected for constitutive expression of inducible nod genes (in the absence of inducer) and screened for hyperinduction of nod genes in the presence of inducer. Mutants which are defective in nodulation or in symbiotic nitrogen fixation are eliminated from further testing. Selections for constitutive nod expression and for hyperinduction of nod genes are facilitated by the use of plasmid carrying a selectable marker fused to an inducible nod gene and a plasmid carrying a reporter gene fused downstream of an inducible nod gene. The methods exemplified are particularly useful for the isolation and identification of Comp.sup.+ mutants of Bradyrhizobium japonicum.