Département de biochimie, microbiologie et bio-informatique de doctorat

Examen

Madame Alessandra Gonçalves de Melo « Genomics, Diversity, and Biology of Brevibacterium linens Phages»

Cet examen de doctorat aura lieu le Jeudi 7 avril à 14 h 00 Local PLT-3370 Pavillon Adrien-Pouliot En présence de

Sylvain Moineau, Ph.D. (Directeur de recherche) Professeur titulaire Département de biochimie, microbiologie et bio-informatique Université Laval Michel Frenette, Ph.D. Professeur titulaire Département de biochimie, microbiologie et bio-informatique Université Laval Steve Labrie, Ph.D Professeur titulaire Département des sciences des aliments Université Laval L’examen sera sous la présidence de Lisa Topolnik, Ph.D. Directrice des programmes d’études supérieures Département de biochimie, microbiologie et bio-informatique

Tous sont invités à cet examen de doctorat

Most cheeses harbor a complex and dynamic microbiota that is characterized by a microbial succession during the manufacturing and ripening processes. The highly heterogeneous physicochemical composition of cheeses as well as the metabolism and physiology of the microorganisms will influence the microbial occupation and growth on smear surface-ripened cheeses. Ultimately, the effect of such growth will determine the final characteristics of these cheeses. Brevibacterium linens is the major component of the bacterial flora present in the smear of a variety of surface-ripened cheeses produced worldwide. Due to its metabolic richness, B. linens contributes to a variety of process during the ripening of cheeses, such as the breakdown of lipids and proteins, and the production of carotenoids pigments and volatile sulfur compounds. Because bacterial strains are widely used by the dairy industry, cheese factories are environments susceptible to phage proliferation. Phage outbreaks can cause delay or interruption of fermentation processes and lead to a downgrade product. In addition, these environments have multiple entries for phages, such as raw milk, the manufacturing environment per se, and the presence of prophages in the bacterial genome. Therefore, an understanding of both phage and host genetics and biology is essential in order to define phage requirements for infection and to determine how phage and host co-evolve to counteract and adapt to the threat posed by the other. Thus, the study of B. linens phage genomics, diversity and biology is important to understand this dynamic. It will also contribute to control phage proliferation in industries that rely on the use of B. linens during cheese ripening. Moreover, the selection of phage-resistant strains of B. linens is a critical point to keep the quality of washed rind cheeses, as phages infecting sensitive strains may emerge in these environments. Thus far, phage infecting B. linens was still a subject unexplored, and no studies were found in the literature focused on this topic. It highlights the relevance of providing novel and unprecedented knowledge on this matter.