Københavns Universitet

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MSc student to work on CRISPR engineering of Salmonella prophages at Københavns Universitet

Introduction

Salmonella enterica serovar Typhimurium is an enteric pathogen infecting both humans and animals. Salmonellosis is an infectious disease that can be transmitted through contaminated food like food products derived from meat, chicken, eggs, animal feed, milk, or vegetables.

Within the past last decades, the prevalence of antibiotic-resistant Salmonella has become a serious global challenge. The extensive use of antibiotics, for instance, as a standard component of domestic animal feed, has led to the emergence of antibiotic resistance Salmonella strains.

Bacteriophages are recognized as strong antimicrobial agents and are already used preventively to eliminate Salmonella in food (SafeGuard, Micreos). In addition, phages can be used to control Salmonella infection in animals (e.g. poultry, pork), to eliminate Salmonella before the animals are processed and made accessible for human consumption. Yet, while the use of phage is considered a very promising alternative to antibiotic treatment, some phages are also carrier of toxins (e.g. botulism toxin, diphtheria toxin, cholera toxin, and Shiga toxin), which can enhance the virulence of the bacteria. In addition, phages contain genes of unknown function that are yet to be characterized and could play a role in virulence.

To tackle this possibility, one strategy is to modify a phage into a puncturing device, namely a Tailocin. Tailocin are Phage tail-like particles missing their head and therefore carrying no genetic material. They are produced by defective prophages inserted into their host DNA, and have evolved as versatile bacterial nanomachines for inter-bacterial competition. Bacteria containing such Tailocin are therefore able to target competing species. When the Tailocin binds to its target, it will contract and perforate the bacterial membrane leading to proton motive force dissipation and therefore the death of the targeted bacteria.

Salmonella enterica serovar Typhimurium strain LT2 is one model strain to study Salmonellosis. Its prophage content has been well characterized and shows four different prophages (Fels-1, -2, Gifsy-1, -2), inducible under different conditions. It is therefore plausible that modified prophage in LT2 strain lacking their capsid or portal genes would only be able to produce headless phage particles (Tailocin), if induced. Harvested Tailocins after purification could then be used as antimicrobial component against Salmonella.

The project has the potential to show that resident prophages within any bacterial host could be modified into an antimicrobial component, opening possibilities for phage therapy.

Aim

The project aim to modify the four prophages within Salmonella enterica serovar Typhimurium strain LT2 to delete their head associated component (e.g. major capsid protein, portal protein), induce the modified head-less prophages, harvest the produced Tailocin particles, purify them and test their antimicrobial activity against the original LT2 strain or strain LT2C emptied of prophages.

Your work

You will produce the Tailocin mutant strain LT2, by knocking out head associated genes within the four resident prophages Fels-1, -2 and Gifsy-1 and -2. You will induce the production of the Tailocin particles, purify them and used them against the native LT2 strain and strain LT2C emptied of prophage. You will also evaluate the Tailocin inhibition effect by quantifying the number of Tailocin particles necessary / bacteria cells.

Methods

Cloning, mutants generation using CRISPR or LamdaRed systems, prophage induction, prophage purification, Tailocin / LT2 challenge assay.

Supervisor

PhD Cedric Woudstra

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