CHAPITRE 4: Discussion
4.3.2 L’ORF 41
Selon la figurer 3.9, les outils bio-informatiques prédisent que l’ORF41, composé de 51 résidus, serait constitué d’une hélice α et de deux feuillets β. Malheureusement, le peptide synthétisé de l’ORF41 n’a pas pu être solubilisé. Sans une solution du peptide, il est impossible de générer des spectres de dichroïsme circulaire et donc les seules données disponibles sur la structure de l’ORF41 sont celles des prédictions bio-informatiques.
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Conclusion et perspectives
Les bactéries et les bactériophages sont au cœur d’une guerre microscopique responsable d’une coévolution rapide. Les phages surpassent de 10 fois le nombre de bactéries sur la planète. Pourtant, la grande majorité des protéines qu’ils codent ont une fonction inconnue. Les génomes de phages sont séparés selon l’expression temporelle des gènes au moment de l’infection (expression précoce, médiane et tardive). Les gènes tardifs sont souvent bien caractérisés, car ils codent pour des protéines structurales, plus faciles à étudier, car le phénotype est observable par microscopie électronique. Toutefois, énormément de gènes précoces et médians codant pour des protéines non structurales n’ont aucune fonction déterminée, malgré le fait qu’ils sont d’une grande importance pour la réplication virale et jouent un rôle majeur dans la régulation. L’outil génétique CRISPR-Cas9, qui a révolutionné le monde de l’édition de génome, permet la modification de ces gènes et ainsi l’étude du phénotype de phages mutants.
Sur les 14 gènes du phage 2972 qui codent pour des protéines aux fonctions inconnues, nous en avons sept, ce qui confirme la robustesse de notre approche expérimentale. De ces sept mutants, trois présentent une difficulté significative au niveau de la réplication virale en conditions de laboratoire. Lorsque le phage 2972 infecte la souche S. thermophilus DGCC7710, approximativement 120 virions sont relâchés dans l’environnement pour chaque cellule lysée. Les phages 2972Δ22, 2972Δ41 et 2972Δ43 ont une progéniture diminuée d’au moins la moitié ou plus. De plus, le phage mutant 2972Δ22 possède aussi une capacité d’adsorption à la surface cellulaire de 30% moins efficace. Plusieurs hypothèses ont été émises quant au rôle que ces protéines peuvent jouer, cependant aucune fonction n’a encore été déterminée avec certitude. Il est connu que la structure d’une protéine est fortement liée à sa fonction. Ainsi, des études préliminaires quant à la structure secondaire de certaines protéines codées par ces gènes ont été entreprises.
En perspective, il est évident que des tests plus approfondis seront nécessaires à chaque gène à l’étude, en plus de la détermination de la structure secondaire des gènes impossible à muter. Il serait aussi très intéressant d’étudier les interactions de ces protéines avec les protéines de l’hôte ou du phage. En somme, les données recueillies permettront une meilleure compréhension des interactions moléculaires entre les phages et les bactéries, ainsi que l’approfondissement des connaissances des mécanismes de réplication et d’infection des bactériophages pour éventuellement perfectionner les méthodes de contrôle appliquées en industrie laitière.
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