Effect of copper stress on growth of T. farahensis in different media: a, 1 µg Cu++/ml/day in Bold-basal medium; b, 1 µg Cu++/ml/day in wheat grain medium; c, 10 µg Cu++/ml/day in modified Neff’s medium. Organisms showed an early death under stress conditions. Arrows indicate maximum resistance/tolerance dose of Cu++ for the cells; d, Comparative growth in modified Neff’s medium in the presence of different concentrations of copper ions (1, 5 and 10 µg/ml/day) showed that low concentrations of copper (1 and 5 µg/ml) had a positive effect on growth rate of T. farahensis.