Characterization of the adsorption and lysis processes of bacteriophages infecting the Bacillus cereus group

The phage replication cycle begins with its adsorption to its host and ends with the release of new virions upon bacterial lysis. These steps are important, not only for the proper conduct of the phage life cycle, but also because proteins mediating attachment and lysis have a significant biotechnological potential. The adsorption step involves viral proteins called receptor binding proteins (RBP) and specific receptors at the host surface, while membrane permeabilization and cell wall degradation leading to lysis are achieved by the concerted actions of holins and endolysins. This thesis aimed to better understand the adsorption and lysis processes of phages targeting the Bacillus cereus group. The first part of this work showed that phage Deep-Blue is a promising candidate for controlling emetic strains, although its narrow host range requires its integration in a phage cocktail. In the second part, the viral proteins involved in the adsorption process were investigated. Comparison of the tail proteins of B. cereus siphoviruses revealed diverse genetic organizations and the prevalence of carbohydrate binding modules (CBM). The role in adsorption of these CBM was experimentally demonstrated for phage Deep-Purple. Regarding myoviruses, Deep-Blue and Vp4 RBP were identified, and their tail regions compared to that of the well-known Listeria phage A511 revealing important differences in key proteins. The third part of this thesis showed that different lysis mechanisms are present in phages infecting B. cereus and that endolysins have a broader activity spectrum than their related phages revealing that they could be used in biocontrol and detection.