Isolation and Characterization of a Glutathione-overproducing, Captan-resistant Mutant of Azospirillum brasilense

The fungicide Captan inhibited the growth of Azospirillum brasilense at a concentration of 25 μg ml-1. When cysteine and glutathione were added to the medium they removed the toxicity of the fungicide. A spontaneous mutant was isolated which was able to grow and fix nitrogen in the presence of 100 μg Captan ml-1. Characterization of the mutant indicated very high levels of glutathione and glutathione transferase activity as compared to the parent strain. The role of these cellular components in the mechanism of resistance to Captan is discussed; the involvement of a selenium-independent glutathione peroxidase appears essential to Captan resistance in the mutant strain.