Characterisation of CBASS antiviral defence system in the Bacillus cereus group

Details

Supervisors

Gillis, Annika

Faculty

Faculté des bioingénieurs

Degree label

Master [120] : bioingénieur en chimie et bioindustries, à finalité spécialisée

Abstract

Bacteriophages (phages), viruses specific to bacteria, are attracting scientific interest for a variety of biotechnological, medical, and agri-food applications. Their use is envisaged as a means of prevention against pathogens such as Bacillus cereus s.l., a group of bacteria known to be a vector of food-borne diseases and ubiquitous in industry. However, the ongoing adaptation of organisms has led to the development of bacterial defence systems, metabolic pathways that have evolved specifically to prevent phage infections. Understanding these systems is crucial to developing the use of phages in industrial settings. Recently discovered systems include Cyclic Oligonucleotide-Based Anti-Phage Signalling Systems also known as CBASS, a family of phage defence systems characterized by its reliance on signalling of cyclic oligonucleotides. These systems promote cell death, preventing the spread of phages to neighbouring cells. The aim of this work is to gain a better understanding of the functioning of CBASS system within the B. cereus group. The main objectives are to study the composition of the system’s cassette and to analyse its mechanism of action within this bacterial group against a variety of phages. Bioinformatics tools were used to study the signalling and effector genes of the CBASS system naturally present in B. cereus VD146. These genes were then transformed into various naïve bacteria, including B. thuringiensis GSX002 and E. coli DH5α, to study the impact of the system's presence on the infection rate of a variety of phages under different conditions. The host range of the bacterial host system was also studied to be able to compare the impact of deletion of the system in the future. The signalling protein was identified as belonging to the nucleotidyltransferase family, involved in the production of cyclic nucleotide second messengers, while the effector protein was identified as belonging to the SMODS-associating four transmembrane effector family, disrupting membrane integrity and leading to cell death. The CBASS system showed promising activity against various B. cereus-infecting phages, although this activity was limited. However, a protective effect was identified and will serve as a basis for future studies. This work also highlighted the impact of host bacteria, type of CBASS cassette and types of infecting phages on the system’s activity. The use of optimal conditions and a suitable vector is also crucial for detecting CBASS expression. Overall, this work provides a better understanding of the interactions of the CBASS systems in the bacterial anti-viral defence, with a range of Bacillus and E. coli phages, and provides insight on a potential antiviral effect of expression vector pHT304-18Z. In the years to come, this understanding will be an essential source of research for developing the use of bacteria and phages in various applications.