Effects of benzidine and benzidine analogues on growth of bacteria including Azotobacter vinelandii

Benzidine and benzidine analogues are mutagenic and carcinogenic metabolites of azo dyes that are widely found in the environment. The toxicities of benzidine and nine of its analogues against 18 bacterial strains including nitrogen-fixing Azotobacter vinelandii were tested using the well diffusion assay technique. 2-Aminobiphenyl and 3-aminobiphenyl were the most inhibitory to all bacterial species tested except A. vinelandii. 4- Aminobiphenyl was inhibitory to the growth of A. vinelandii using a plate count assay, although it failed to show an inhibitory effect in the well diffusion assay. 3,3'-4,4'-Tetraaminobiphenyl was inhibitory to both A. vinelandii and Aeromonas hydrophila, whereas benzidine, 3,3'- dimethoxybenzidine, 4,4'-dinitro-2-bipheny-lamine, 3,3'-5,5'- tetramethylbenzidine, N,N-N',N'-tetramethylbenzidine, and o-tolidine were not inhibitory to any of the bacterial species tested. Of all these compounds tested, only 3,3'-4,4'-tetraaminobiphenyl and 4-aminobiphenyl inhibited the nitrogenase activity of A. vinelandii.