oa Bacteriocins from Qatari Bacillus Thuringiensis Crystal Producing Strains

Antimicrobial agents are very useful and have been the subject of intense research. Amongst these compounds, bacteriocins are defined as peptide antibiotics which do not harm the producer strain but have the ability to kill closely related bacteria. Bacillus thuringiensis is a friendly bacterium best known for the production of bioinsecticides, but is also considered as a source of bacteriocins active against the closely related pathogenic species harmful for food products, and many organisms.

The major goal of this project is to evidence and characterize novel Bacillus thuringiensis bacteriocins synthesized by Qatari Bacillus thuringiensis strains. In order to obtain that, many approaches have been adopted:

- Screening of delta-endotoxin producing strains of Bacillus thuringiensis.

- Screening of bacteriocin producing strains of Bacillus thuringiensis.

- Study of the antagonistic effects among bacteriocin producing strains.

- Study of the effect of medium composition on bacteriocin synthesis.

- Screening by PCR of Bacthuricin F4 like producing strains.

In order to screen the bacteriocin producing strains of Bacillus thuringiensis, many techniques have been utilized such as: Direct Antagonism on Solid Media and Well Diffusion Method to check the bacteriocin activity. Bacteriocin production was studied on different growth media and against various indicator strains.

The screening of 192 Bacillus thuringiensis strains isolated from Qatar, allowed the evidence of strains having different crystal forms. In fact, these strains produce parasporal crystals that have pyramidal, bipyramidal, cubical, spherical and amorphous forms. Among these Bacillus thuringiensis strains, about 70% produce spherical crystals and 30 % bipyramidal. Similar results were obtained in the laboratory by Sara Zakzok and Duha Rabah. This could be considered as a contribution to the establishment of Qatari bacterial gene bank. Screening the collection for bactericidal activities against indicator strains, revealed a variability in the size and aspect of the inhibition zones. About 76% of the collection were bacteriocin producing strains and only 24% were negative.

There have been noticed many signs of novelty among our local bacteriocin producing strains. These results are very encouraging and in favour of the use of B. thuringiensis local strains for bacteriocin production.