Involvement of Tn4430 in transfer of Bacillus anthracis plasmids mediated by Bacillus thuringiensis plasmid pXO12

The self-transmissible plasmid pXO12 (112.5 kilobases [kb]), originally isolated from strain 4042A of Bacillus thuringiensis subsp. thuringiensis, codes for production of the insecticidal crystal protein (Cry+). The mechanism of pXO12-mediated plasmid transfer was investigated by monitoring the cotransfer of the tetracycline resistance plasmid pBC16 (4.2 kb) and the Bacillus anthracis toxin and capsule plasmids, pXO1 (168 kb) and pXO2 (85.6 kb), respectively. In matings of B. anthracis donors with B. anthracis and Bacillus cereus recipients, the number of Tcr transcipients ranged from 4.8 x 10(4) to 3.9 x 10(6)/ml (frequencies ranged from 1.6 x 10(-4) to 7.1 x 10(-2), and 0.3 to 0.4% of them simultaneously inherited pXO1 or pXO2. Physical analysis of the transferred plasmids suggested that pBC16 was transferred by the process of donation and that the large B. anthracis plasmids were transferred by the process of conduction. The transfer of pXO1 and pXO2 involved the transposition of Tn4430 from pXO12 onto these plasmids. DNA-DNA hybridization experiments demonstrated that Tn4430 was located on a 16.0-kb AvaI fragment of pXO12. Examination of Tra- and Cry- derivatives of pXO12 showed that this fragment also harbored information involved in crystal formation and was adjacent to a restriction fragment containing DNA sequences carrying information required for conjugal transfer.