Fig. 1.

The response of xan cluster mutants to copper stress yields a copper-dependent pigmentation phenotype. (A) The xan gene cluster responsible for the production of xanthocillin derivatives contains seven genes: xanA (ThiJ/Pfp1 domain protein with homology to isocyanide hydratases; red), xanB (two-domain isocyanide synthase-dioxygenase; blue), xanC (C6 transcription factor; yellow), xanD (DUF4149 domain protein; gray), xanE (O-methyltransferase; purple), xanF (conserved hypothetical protein; gray), and xanG (P450 monooxygenase homology to the yeast enzyme Dit2; green). (B) Growth of OE::xanC mutants on solid GMM supplemented with CuSO₄. (C) Sporulation of xanC mutants on solid GMM. (D) ABTS laccase activity assay of xanC mutants when grown on solid media supplemented with CuSO₄. Statistical analyses were performed using Student’s t test, and shown is the mean with SEM of three replicates. OE, OE::xanC; Δ, ΔxanC; WT, wild type (*P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001).