Figure 1. Selection of mutants with increased tellurite resistance.

(a) Summary of directed evolution experiment in LB medium. The number of serial passages (one passage=growth for 24 h) and the concentration of tellurite used is indicated. Strain EM2 was isolated at passage 26. Representative growth curves of strains BW25113 and EM2 in (b) LB or (c) M9 medium in the presence of the indicated tellurite concentrations. Values represent the mean of three biological replicates. In (c) s.d. was removed for clarity (growth curves with s.d. are shown in Supplementary Fig. 2). (d) The indicated strains were grown in M9 medium and the heme and ALA content was measured in cell extracts. The level of heme or ALA in strain EM2, EM42 and EM43 were compared to strain BW25113, which was arbitrarily set to 100%. Values represent the mean of three biological replicates. Error bars represent s.d. TeO₃²⁻: tellurite **P<0.001; ***P<0.0001 as determined by t-test.