Genetic analysis of Azotobacter vinelandii mutant strains unable to fix nitrogen.

Transformation was used to perform ratio test crosses with mutant strains of Azotobacter vinelandii unable to fix N2. Mutations that simultaneously eliminated both components of nitrogenase (nif-1 and nif-2) were tightly linked. The nif-45 mutation that resulted in the absence of an active molybdenum cofactor was closer to nif-1 and nif-2 than to any of the other nif mutations. Strains that lacked component I carried mutations that were closely linked to each other. Mutations that probably were located in the structural genes for components I and II appeared to be relatively close to each other on the A. vinelandii genome.