Bacillus subtilis 168 was developed as a genome vector to manipulate large DNA fragments. The system is based on the inherent natural transformation (TF) activity. However, DNA size transferred by TF is limited up to approximately 100 kb. A conjugal transfer system capable of transferring DNA fragments considerably larger than those transferred by TF was developed. A well-defined oriT110 sequence and a cognate relaxase gene from the pUB110 plasmid were inserted into the xkdE gene of the B. subtilis genome. Transfer of antibiotic resistance markers distant from the oriT110 locus to the recipient B. subtilis occurred only in the presence of pLS20, a helper plasmid that provides a type IV secretion system. Marker transmission was consistent with the orientation of oriT110 and required a recA-proficient recipient. The first conjugal transfer system of genomic DNA should provide a valuable alternative genetic tool for editing the B. subtilis genome.
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