Figure 2. Construction of host strain B. subtilis BUK.

(A) Two homologous arms of upp gene (Upp-F and Upp-B) were cloned into pUC18, and the arabinose-inducible comK expression cassette was fused downstream of the front homologous arm to construct vector pST. (B) The sequence between two homologous arms of upp gene (Upp-F and Upp-B), was replaced by comK cassette via a double-crossover recombination. Crossed lines indicated double-crossover recombinant events. Upp-F and Upp-B, upstream and downstream fragment of upp gene, respectively; comK, the master regulator ComK encoding gene for B. subtilis competence development; P_ara, arabinose-inducible promoter of ara operon; araR, arabinose operon transcriptional repressor of B. subtilis.