Factors Affecting Bacteriocin Production by Bacillus thuringiensis from Stock Cultures Isolated from Middle Tennessee

Fahdah Alshammari, Tennessee State University


Bacillus thuringiensis (Bt) is a gram-positive spore forming soil dwelling bacterium that is toxic against insect pests. Bt strains produce many proteins, including bacteriocin which is an inhibitory substance to other bacteria. Bacteriocins, originally thought to be produced primarily by Enterobacteriaceae, are now known to be produced by many bacterial species. Bacteriocins by Bt are of value because of the ease of production and scale up of the organism. Bacteriocins are active against many gram-positive bacteria, though some can also inhibit gram-negative species. In this project, a stock of 66 Bt strains isolated from Middle Tennessee was tested for the presence of bacteriocin. The agar well diffusion method was used to determine if the strains had any bacteriocin activity. The strains were cultured in LB broth medium at 30°C for 24 hours, and the cells were removed by centrifugation. The supernatant was filter-sterilized and Bacillus cereus (CB154870A), Escherichia coli (CB155065A), Staphylococcus aureus (CB155554A), and Pseudomonas aeruginosa (CB155250A) were used as indicator organisms. These bacteria were seeded onto agar plates to assess any antimicrobial activity. It was found that 32 of the Bt strains tested produced a bacteriocin. This was evidenced by a clear zone on the plates indicating that a bacteriocin was produced. The bacteriocins were extracted from the Bt strains and characterized based on the sensitivity to heat, various pH values, and proteinase k. It was found that bacteriocins were sensitive to low and high pH values and high temperatures. The activity of bacteriocin was disappeared after adding proteinase K in all Bt strains except Bt 71. In conclusion, 32 of the 66 strains of Bt demonstrated the presence of a bacteriocin, and this activity in one strain was due to a non-protein molecule. Further studies will include the determination of the minimal inhibitory concentration (MIC) of the bacteriocins, and characterizing the chemical nature of the most effective bacteriocins from the Bt strains.

Subject Area

Biology|Microbiology|Molecular biology|Pharmaceutical sciences

Recommended Citation

Fahdah Alshammari, "Factors Affecting Bacteriocin Production by Bacillus thuringiensis from Stock Cultures Isolated from Middle Tennessee" (2020). ETD Collection for Tennessee State University. Paper AAI27830036.