Genome stability of Bacillus thuringiensis subsp. israelensis isolates

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Bacillus thuringiensis subsp. israelensis (Bt. israelensis) is a bacterium known for its mosquitocidal toxins.
• Understanding the genetic diversity of Bt. israelensis is crucial for its application and evolutionary studies.

Purpose of the Study:

• To assess the genetic diversity among Swedish soil isolates of Bt. israelensis serotype H14.
• To compare these isolates with reference strains using various molecular techniques.
• To investigate the potential for horizontal gene transfer of mosquitocidal toxin genes.

Main Methods:

• Multilocus enzyme electrophoresis (MLEE) to analyze enzyme polymorphisms.
• Random amplified polymorphic DNA (RAPD) analysis for DNA fingerprinting.
• Pulse field gel electrophoresis (PFGE) for large-scale DNA fragment analysis.
• Southern blotting with probes for flagellin and mosquitocidal toxin genes.

Main Results:

• RAPD and MLEE analyses indicated high genetic similarity among Bt. israelensis H14 strains, with only one strain showing a minor allelic difference.
• PFGE revealed a conserved genetic backbone but identified variations in a specific SfiI restriction fragment.
• Southern blot analysis confirmed the presence of mosquitocidal toxin genes in H14 strains, with one strain (6:3) exhibiting toxin gene hybridization despite being genetically distinct from other H14 strains.

Conclusions:

• Swedish Bt. israelensis H14 soil isolates exhibit remarkable genetic uniformity.
• The presence of mosquitocidal toxin genes in the genetically distinct strain 6:3 suggests a possible occurrence of horizontal gene transfer.
• Further investigation is warranted to confirm gene transfer mechanisms in Bt. israelensis.