[Simple photometric and fluorometric assays are insufficient for assessing UV-induced mutagenesis in genes controlling tryptophan synthesis in Escherichia coli].

A new approach to detecting induced mutations was tested based on the assay of cell extracts and special growth media following cultivation of UV irradiated Escherichia coli cells. No correlation was found between the UV dose and the optical densities of cultural media or cell extracts prepared by Triton X-100 treatment. Blue fluorescence of concentrated cultural media varied with cell dose, according to a rather complex law, which differed substantially from the known dose-effect curves for induced mutations. Nevertheless, a certain extent of the brown staining of tryptophan containing medium could, presumably, serve as a quite sensitive indicator of the integral metabolic activity of bacteria grown in the medium. Besides, we observed that overnight lag phase cultures became gradually more transparent, when analysed in the spectrophotometer cuvette just after their dilution with fresh medium.