Thuricin: the bacteriocin produced by Bacillus thuringiensis.

Area of Science:

• Microbiology
• Bacteriology
• Molecular Biology

Background:

• Bacillus thuringiensis (Bt) is a Gram-positive bacterium known for its insecticidal properties.
• Some Bt strains produce bacteriocins, antimicrobial peptides toxic to related bacterial species.
• The characterization of these bacteriocins is crucial for understanding bacterial competition and developing novel antimicrobials.

Purpose of the Study:

• To characterize the antibacterial substance produced by Bacillus thuringiensis serovar, thuringiensis (HD-2).
• To determine the nature, properties, and mode of action of this bacteriocin, named thuricin.
• To investigate the genetic basis of thuricin production.

Main Methods:

• Antibacterial activity assays against various bacterial strains.
• Purification using gel filtration chromatography and ultracentrifugation.
• Characterization using nondenaturing and SDS-PAGE, enzyme treatments, and electron microscopy.
• Plasmid analysis to correlate genetic elements with toxin production.

Main Results:

• Thuricin exhibited broad-spectrum activity against B. thuringiensis and other Gram-positive bacteria, but not Gram-negative species.
• Native thuricin has a high molecular weight (Mr > 950,000) and is proteinaceous, sensitive to proteases and heat.
• Thuricin possesses phospholipase A activity, which is adsorbed by sensitive cells and can be blocked by phospholipids, suggesting a lytic mechanism.
• Loss of a 150-MDa plasmid correlated with the loss of thuricin production.

Conclusions:

• Thuricin is a large, proteinaceous bacteriocin produced by B. thuringiensis serovar, thuringiensis.
• Its antibacterial activity involves phospholipase A activity and a bacteriolytic effect on sensitive strains.
• Thuricin production is dependent on a 150-MDa plasmid, highlighting the role of extrachromosomal elements in bacteriocin synthesis.