RESUMEN
A central portion of nifS, designated nifS', was amplified from Azotobacter vinelandii. The nifS' was cloned into pUC18 to make pUCS. Then pUCS was integrated into Azotobacter vindandii chromosome DNA by homologous recombination. This nifS disruption mutants were generated by single cross-over event and selected by Amp resistence on BBGN medium. The nifS disruption mutant (named SU1) was affirmed by southern blot and PCR amplification. SU1 grows rapidly on BBGN, but very slowly on Burk's N-free medium. This phenomenon showes that SU1 nearly lost its nitrogen fixation ability because of the disruption of nifS. The successful construction of SU1 is helpful for further research on the effect of nifS on the structure and function of nitrogenase component-Ⅰ and Ⅱ.