Day 1 :
Qatar University, Qatar
Keynote: Bacillus thuringiensis: A source of environmentally safe and sustainable bioinsecticides and bacteriocins
Time : 11:15-12:10
Samir Jaoua, has completed his PhD at the age of 27 years from the University of Technology of Compiegne (UTC, France), and postdoctoral studies from Ciba-Geigy (Novartis) in Basle (Switzerland). He is Professor of Microbiology at the Department of Biological and Environmental Sciences (CAS, Qatar Univ.). He is also Qualified Professor of France Universities “Section 64: Molecular Biology and Biochemistry” and Professor at the University of Sfax (Tunisia). Prof. Samir Jaoua is molecular and microbial geneticist. He has published 126 papers in reputed journals. His H-index is 32 with 3125 citations.
Bacillus thuringiensis (Bt) bioinsectices have been recognized as the most successful, environmentally safe and sustainable agents controlling insect pests. In the present study, more than 600 Bt (QBT) strains were isolated from Qatar soil. The exploration of these Bt isolates was based on the proteomics of the crystal d-endotoxins, responsible of the insecticidal activity and on the bacteriocins that are peptide antibiotics and the investigation of the corresponding genes. Bt crystals showed different forms, with the highest ratio of spherical ones. Among the spherical crystals, four different morphologies were observed. The proteomic content of parasporal crystals from each Bt isolate revealed that there are 16 different protein profiles. On the other hand, plasmid pattern analysis showed that the collection has only 7 different plasmid profiles. These QBT strains harbour genes cry4B, cry11, cyt1a , cry2, vip3A and cry1Ia depending on their crystal forms. Many gene sequences show polymorphism compared to reference strains cry genes and others cyt genes encoding cytotoxicity against cancer cells. 19 Bt israelensis strains have been identified as candidates for d-endotoxin production targeting dipteran insects and disease vectors. The insecticidal activity of the crystal proteins showed variable LC50 against Aedes aegypti. On the other hand, we investigated the activities of various bacteriocins produced by Bacillus thuringiensis strains. 25% of the collection of strains have shown bacteriocin activities against the pathogenic bacteria such as Bacillus cereus and Staphylococcus aureus at 30oC. Bacteriocin production was found to be dependent on media composition, type of substrate (solid/liquid), temperature, physiological state of the cells and presence of plasmids. Plasmid cured Bt. 4Q7 produced a 100oC thermostable glycoprotein type bacteriocin. QBT466 produced a heat-sensitive bacteriocin that specifically killed S. aureus cells very quickly. All these bacteriocins have novel characteristics that have not been previously reported and might have important applications in probiotics and human microbiome.
University of Pennsylvania, USA
Time : 10:00-10:55
Dr. Akira Kaji received his PhD in Biological Sciences from Johns Hopkins University in 1958 and conducted postdoctoral research at the Rockefeller Institute, Vanderbilt School of Medicine, and the Oak Ridge National Laboratory. He obtained a faculty position at the University of Pennsylvania, which he still maintains. He has over 200 publications in reputed journals. He has two notable discoveries among his many contributions. First is the discovery of the binding of tRNA to the mRNA/ribosome complex, which contributed to Nirenberg’s breakthrough in the discovery of genetic code. Dr. Kaji also determined the fourth step of protein synthesis, ribosome recycling.
Ribosome recycling factor (RRF) is known to catalyze three separate reactions: release of tRNA, release of mRNA, and splitting of the ribosome. We used E. coli harboring temperature sensitive (ts) RRF and followed downstream reading of translationally coupled ORF. At the non-permissive temperature, ribosomes remained on the termination codon of the junction sequence (UAAUG) of coupled ORFs and translated downstream ORF. When upstream ORF was short, translation of the downstream reading was abolished, suggesting that the ribosomes released by RRF are moving toward the Shine-Dalgarno (SD) sequence of the upstream ORF. Thermal frame shift at the stop codon was also stopped by the upstream SD sequence. Our data suggest that the ribosome-bound mRNA may take a secondary structure around the junction sequence. For in vitro studies, we used mRNA that incorporated different radioactively labeled amino acids based on frameshift at the junction sequence of two translationally coupled ORFs. In the absence of RRF, the ribosome stayed on the mRNA and translated in frame with the termination codon UAA. In the presence of RRF, amino acid incorporation occurred in frame with the start codon AUG. This suggests that RRF releases the ribosome from UAA and the released ribosome binds to AUG and begins translation. With the use of tethered, unsplittable ribosomes (Ribo-T), we showed that complete ribosomal splitting is not required for the action of RRF in translational coupling. Therefore, the main role of RRF in translational coupling appears to be the release of ribosomes from mRNA.