Bacillus subtilis offers a platform for giant DNA synthesis, which is mediated by the connection of overlapping DNA segments called domino DNA, in the cloning locus of the host. The domino method was successfully used to produce DNA fragments as large as 3500 kbp. However, domino DNA is limited to <100 kbp because of size restrictions regarding the transformation (TF) of B. subtilis competent cells. A novel conjugal transfer (CT) method was designed to eliminate the TF size limit. The CT method enables rapid and efficient domino reactions in addition to the transfer of giant DNA molecules of up to 875 kbp to another B. subtilis genome within 4 hours. The combined use of the TF and CT should enable significantly rapid giant DNA production.