Recent aspects of genetic manipulation in Bacillus thuringiensis

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• The conjugative plasmid pAM beta 1 facilitates genetic exchange between bacterial species.
• Bacillus thuringiensis produces crystal proteins with insecticidal properties, often encoded by plasmids.
• Understanding plasmid-host interactions is crucial for genetic engineering and bacterial evolution.

Purpose of the Study:

• To investigate the transfer of the conjugative plasmid pAM beta 1 between Streptococcus faecalis and Bacillus thuringiensis.
• To characterize novel DNA sequences associated with pAM beta 1 in B. thuringiensis.
• To analyze the structure of crystal genes in relation to host plasmids and associated DNA sequences.

Main Methods:

• Filter-mating was employed for conjugative plasmid transfer experiments.
• Restriction mapping was used to compare plasmid and chromosomal crystal genes.
• Cloning of B. thuringiensis crystal genes in E. coli facilitated detailed analysis.

Main Results:

• Successful transfer of pAM beta 1 from S. faecalis to B. thuringiensis was achieved.
• A 3 Md DNA sequence (Th sequence), related to B. thuringiensis host plasmids, was identified as an in vivo insertion into pAM beta 1.
• Reciprocal transfer of pAM beta 1 from B. thuringiensis to S. faecalis was demonstrated.
• Comparison of crystal genes revealed two classes differing mainly in the 3' region.
• The Th sequence was frequently found associated with crystal genes on host plasmids, suggesting a model for their organization.

Conclusions:

• The Th sequence represents a mobile genetic element potentially influencing crystal gene organization in B. thuringiensis.
• Plasmid transfer and integration mechanisms play a role in the genetic diversity of B. thuringiensis.
• Structural variations in crystal genes may impact the properties of insecticidal proteins.