Bacillus subtilis (natto) plasmid pLS20 mediates interspecies plasmid transfer

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Abstract
The 55-kilobase plasmid, pLS20, of Bacillus subtilis (natto) 3335 promotes transfer of the tetracycline resistance plasmid pBC16 from B. subtilis (natto) to the Bacillus species B. anthracis, B. cereus, B. licheniformis, B. megaterium, B. pumilus, B. subtilis, and B. thuringiensis. Frequency of pBC16 transfer ranged from 2.3 x 10(-6) to 2.8 x 10(-3). Evidence for a plasmid-encoded conjugationlike mechanism of genetic exchange includes (i) pLS20+ strains, but not pLS20- strains, functioned as donors of pBC16; (ii) plasmid transfer was insensitive to the presence of DNase; and (iii) cell-free filtrates of donor cultures did not convert recipient cells to Tcr. Cotransfer of pLS20 and pBC16 in intraspecies matings and in matings with a restriction-deficient B. subtilis strain indicated that pLS20 was self-transmissible. In addition to mobilizing pBC16, pLS20 mediated transfer of the B. subtilis (natto) plasmid pLS19 and the Staphylococcus aureus plasmid pUB110. The fertility plasmid did not carry a selectable marker. To facilitate direct selection for pLS20 transfer, plasmid derivatives which carried the erythromycin resistance transposon Tn917 were generated. Development of this method of genetic exchange will facilitate the introduction of plasmid DNA into nontransformable species by use of transformable fertile B. subtilis or B. subtilis (natto) strains as intermediates.