Growth modification of Euglena gracilis Klebs after 2-benzamido-5-nitrothiazole derivatives application.

The toxic effect of 2-benzamido-5-nitrothiazole (BNT) and 11 of its derivatives on the growth of Euglena gracilis was studied in vitro and compared with that of niclosamide. These compounds inhibit proliferation of algae or, at low concentrations, stimulate proliferation. BNT and all its derivatives had an inhibiting effect that was less pronounced, however, than with niclosamide in most instances. The most active compounds were 3,5-dichloro-BNT at pH 3.5 and 7.2. Growth activation was studied by determining the maximal activation concentration. BNT and its derivatives stimulated E. gracilis growth at low concentrations in an acidic environment. This effect was more variable in an environment at neutral pH.