The Staphylococcus aureus plasmids pC194 and pUB110 were introduced into Bacillus thuringiensis subsp. israelensis by using the Streptococcus faecalis transposon Tn916 as a mobilizing agent. Plasmid transfer occurred only when B. thuringiensis subsp. israelensis was mated with a B. subtilis donor that contained both pC194 and pUB110 and Tn916; plasmid transfer was not observed in the absence of the transposon. B. thuringiensis transconjugants resistant to chloramphenicol (Cmr) and tetracycline (Tetr) were detected at a frequency of 1.96 x 10(-6) per recipient cell, whereas the Tetr phenotype, but not the Cmr, was observed at a frequency of 1.09 x 10(-4). The converse, Cmr but not Tetr, was observed at a frequency of 2.94 X 10(-5). The transfer of pUB110 from B. subtilis to B. thuringiensis subsp. israelensis was observed at a frequency of 3.0 x 10(-6) per recipient cell but concomitant transfer of pUB110 and Tn916 was not observed. Mobilization of plasmid pE194 was not observed under these conditions. Transconjugants were detected in filter matings only, not in broth. The Tn916 phenotype was maintained during serial passage of B. thuringiensis without selection, whereas the pC194 phenotype was not. Unlike pC194, however, pUB110 remained stable in B. thuringiensis during several passages through nonselective medium. Southern hybridization analysis demonstrated that Tn916 had inserted into several different sites on the B. thuringiensis chromosome and that pC194 and pUB110 were maintained as an autonomous plasmid.