Conjugational transfer kinetics of pLS20 between Bacillus subtilis in liquid medium

pLS20-mediated conjugational transfer between Bacillus subtilis was investigated not on conventional solid media but in liquid culture. Detailed conjugational kinetics revealed that pLS20 transmission occurred at a limited cellular growth stage of both donor and recipient. Mutation of the recipient recA did not significantly interfere with the conjugational transfer process.

Experimental Basis for a Stable Plasmid, pLS30, to Shuttle between Bacillus subtilis Species by Conjugational Transfer

The use of Bacillus subtilis 168 as the initial host for molecular cloning and subsequent delivery of the engineered DNA to other Bacillus hosts appears attractive, and would lead to an efficient DNA manipulation system. However, methods of delivery to other Bacillus species are limited due to their inability to develop natural competence. An alternative, unexplored conjugational transfer method drew our attention and a B. subtilis native plasmid, pLS30, isolated from B. subtilis (natto) strain IAM1168 was characterized for this aim. The nucleotide sequence (6,610 bp) contained the mob gene and its recognition sequence, oriT, that features pLS30 as a mobile plasmid between Bacillus species on conjugational transfer. Plasmid pLS3001, a chimera with a pBR322-based plasmid prepared in Escherichia coli to confer an antibiotic resistance marker, showed apparent mobilizing activity in the pLS20-mediated conjugational transfer system recently established. The rep gene and associated palT1-like sequence common to all other pLS plasmids previously sequenced indicated that pLS30 is a typical rolling circle replicating (RCR) type plasmid. Due to the significant stability of pLS30 in IAM1168, application of a mobile plasmid would allow quick propagation to Bacillus species.