Positive selection of nodulation-deficient Rhizobium phaseoli.

A high proportion of Rhizobium phaseoli mutants that survived infection with phage F1 were found to be nodulation deficient. Two that were examined in detail had internal defects in addition to the expected surface defects. One internal defect was in the enzyme phosphoglucose isomerase. The use of phages to select appropriate mutants should apply generally in any system in which surface components are involved.