Isolation and characterization of mutants of cowpea Rhizobium defective in nitrate uptake system

In this communication, two mutants of cowpea Rhizobium CB756 (NR-18 and NR-23), defective in nitrate uptake system, were described. They failed to grow in a medium where nitrate was the sole source of nitrogen and unable to show nitrate reductase activity in cell suspensions. However, they showed nitrate reductase activity (to the level of wild type) in cell-free extract preparations. Thus it appears that in these mutants, the transport genes of nitrate uptake were affected and the synthesis of nitrate induced permease, as its role in nitrate uptake is indicated here, is defective.