Induced natural competence by xylose-driven ComK expression. (A) pMMcomK, vector for xylose-inducible ComK expression. Open reading frames are depicted as arrows. Restriction enzymes are abbreviated. ComK, the main activator for natural competence; ′YhjD, gene downstream of comK, part of a hypothetical protein; XylR, xylose repressor; RepU, replication protein; Tet, tetracycline resistance (Bacillus); Amp, ampicillin resistance (E. coli); ori pBC16, Bacillus origin of replication; ori pBR, ColE1 origin of replication. (B) Growth curves of B. licheniformis MW3.1 pMMcomK with or without the induction of ComK expression. Black circles, induction with 0.25% xylose; gray circles, induction with 0.125% xylose; black and gray squares correspond to uninduced controls. (C) Prototrophic transformants per microgram of DNA of induced (0.125% xylose and 0.25% xylose) and not induced (without) cultures for 2- and 3-h induction times.