The potential toxicity of samples collected at three different cycle stages, namely WWfeed at the feeding phase, WWanaer at the end of the anaerobic reaction, and WWfinalat the end of aeration, were compared for two representative FSBR1 (Fig. 6) or GSBR1(Fig. 7) cycles. The FSBR1 selected cycles correspond to days 21and 29 in Fig. 2 and the GSBR1 ones correspond to days 25 (Fig. 2)and 71 (not shown). The feed solution with 20 mg L−1AR14, prior to treatment (WWfeed), exerted no inhibitory effects on yeast growth(relative to WWcontrol, feed solution without dye; Figs. 6A and 7A).Moreover, for WWfeed the transcript levels of the yeast genes use das indicators of toxicity remained essentially unchanged relative to WWcontrol (Figs. 6B and 7B). Overall, these results suggest no toxicity of the azo dye towards the model yeast. On the contrary, the samples collected at the end of the anaerobic (WWanaer) and aerobic (WWfinal) reaction phases of a typicalFSBR1 cycle appeared to be potentially cyto- and genotoxic since considerable inhibition of yeast growth (>90% relative to control)and induction of gene expression (1.8 < fold change values < 2.8,depending on the indicator gene) occurred (Fig. 6A and B, respectively). Nevertheless, the toxicity decreased slightly from day 21to day 29; this was mostly evidenced by the decreases in the Fig